Symmetric Dimethylarginine: Improving the Diagnosis and Staging of Chronic Kidney Disease in Small Animals

CYSTOCENTESIS AND URINALYSIS IN ZOOMEDICINE: AN UNDERESTIMATED TOOL FOR LARGE FELID STANDARD HEALTH CHECKS

Chronic kidney disease (CKD) is a prevalent disease among felids; yet its origin is still poorly understood, and the disease often remains asymptomatic for years, underscoring the need for early diagnosis. This study aimed to investigate the diagnostic value of urinalysis in accurately staging CKD, particularly as routine health checks in large felids often overlook its significance. In this research, ultrasound-guided cystocentesis (UGC) was performed on 50 captive nondomestic felids during routine veterinary health checks under general anesthesia. Urinalysis included microscopic examination of the sediment, measurement of urine specific gravity (USG) and protein to creatinine ratio (UPC). Additional serum kidney markers, such as creatinine and symmetric dimethylarginine, were compared with USG and UPC to assess their diagnostic value as urinary biomarkers. The results demonstrated proteinuria (UPC > 0.4) or borderline proteinuria (UPC 0.2-0.4) in 49% of the animals. Among these cases, 62% were of renal origin, and 38% were postrenal causes. USG was significantly higher in felids with borderline proteinuria compared to those with proteinuria. A moderate, but significant negative correlation between serum parameters and USG was observed, emphasizing the importance of assessing both diagnostic parameters during kidney evaluations. Additionally, felids with CKD have an increased risk of urinary tract infections, necessitating microscopic urinalysis and bacterial culture analysis. Abnormalities, including hematuria, pyuria, crystalluria, and bacteriuria, were found in approximately 38% of cases through microscopical examination of urine. No complications associated with UGC were observed and abnormal findings were detected in 60% of the cases. Based on these results, the authors recommend the inclusion of UGC and urinalysis as standard diagnostic tools in general health checks for nondomestic felids. This approach provides valuable insights into the early detection and staging of CKD, supporting early intervention and supportive medical care to prolong renal health in these animals.

Bilateral Global Nephrocalcinosis in a Uremic Puppy

This study explores kidney disease in young dogs, focusing on early diagnosis, management, and the importance of staging for effective treatment. Highlighting mineral metabolism imbalances and complications such as nephrocalcinosis, the study presents a case of severe renal failure with uremic syndrome and bilateral nephrocalcinosis in a 50-day-old puppy. Despite intensive care, the puppy's condition deteriorated rapidly, leading to euthanasia. The study underscores the challenges in diagnosing and managing canine nephrocalcinosis in young animals. It emphasizes the need for further research to improve the understanding and treatment outcomes in such cases, ultimately enhancing the quality of life for animals suffering from this rare condition.

Reference Interval Creation for Symmetric Dimethylarginine (SDMA) in Healthy Hispaniolan Amazon Parrots (Amazona ventralis) and Quaker Parrots (Myiopsitta monachus)

Renal disease is often identified as a cause of morbidity and mortality in avian patients. However, currently, early antemortem detection of renal disease in avian patients is difficult. Anatomical and physiological differences between mammals and birds mean the use of commonly employed diagnostic testing (ie, measurement of blood urea nitrogen [BUN] and serum creatinine, urinalysis, and ultrasonography) are either nondiagnostic or difficult to achieve. Symmetric dimethylarginine (SDMA) is considered a more sensitive marker for renal disease in humans, dogs, and cats. However, SDMA has not yet been assessed for diagnostic use in any psittacine species. In this study, we establish reference ranges for SDMA in both Hispaniolan Amazon parrots (Amazona ventralis, HAP) and Quaker parrots (Myiopsitta monachus, QP). Blood was collected from 23 Amazon parrots and 32 Quaker parrots maintained in research facilities. Measurement of SDMA through a commercially available immunoassay (IA-SDMA) as well as creatinine, BUN, uric acid, phosphorus, calcium, sodium, potassium, and chloride were determined through IDEXX Laboratories. Plasma SDMA concentrations ranged from 6 to 15 µg/dL and 3 to 15 µg/dL for the HAP and QP, respectively. Sex was a confounding factor for the QP population, but sex did not have a significant effect on SDMA for the HAP population. No significant correlations were identified between SDMA concentrations and other parameters in either psittacine species. Our results show proof of concept for the IA-SDMA and provide reference intervals for SDMA in HAP and QP. Further investigation is required to determine the validity of this assay and the predictive power of SDMA in the detection of renal impairment for parrots and other common companion birds.

Description of serum symmetric dimethylarginine concentration and of urinary SDS-AGE pattern in dogs with ACTH dependent hyperadrenocorticism

Serum symmetric dimethylarginine (SDMA) and patterns of urinary protein separated by sodium dodecyl sulfate agarose gel electrophoresis (SDS-AGE) have not been investigated as biomarkers in dogs with ACTH-dependent hyperadrenocorticism (ADHAC). This exploratory prospective study aimed to evaluate SDMA, serum creatinine (sCR), and SDS-AGE in dogs with ADHAC with and without proteinuria (ADHAC-P and ADHAC-nP, respectively). Thirty-five pet dogs classified as ADHAC-P (n=16), ADHAC-nP (n=6) and healthy (n=13) were included. Renal biomarkers were evaluated in all dogs at diagnosis. Baseline concentration of SDMA was not significantly different between the three groups (P = 0.15) whereas sCr was significantly lower in dogs in ADHAC dogs compared to healthy dogs (88.0 µmol/L [70.4-132.6; 79.2-114.4]) whether they had proteinuria or not (P = 0.014 and 0.002, respectively). However, baseline concentrations of sCr and SDMA were not significantly different between dogs with ADHAC-P dogs (SDMA, 8 µg/dL [5-12; 7-9]; sCr, 57.2 µmol/L [35.2-212.2; 52.8-92.4]) and ADHAC-nP dogs (SDMA, 8.5 µg/dL [7-13; 8-10]; sCr, 70.4 µmol/L [61.6-79.2; 61.6-70.4]) (P = 0.35 and P = 0.41, respectively). Proteinuria in dogs with ADHAC-P was mainly of glomerular origin (SDS-AGE pattern: glomerular in 10/16 dogs; mixed glomerular/tubular in four dogs). In our study, SDMA was neither significantly different in dogs with ADHAC whether they were proteinuric or not, nor between ADHAC and healthy dogs. Urinary electrophoresis provides additional information to the UPC and further investigations are needed to determine whether it may help identify dogs with ADHAC-P requiring specific antiproteinuric treatment.

Use of amlodipine in the treatment of cats with systemic hypertension in Japan

An increase in systemic blood pressure causes bleeding and ischemia owing to peripheral vascular breakdown, leading to various forms of organ damage. The brain, eyes, kidneys, and cardiovascular system are known target organs for hypertension. To our knowledge, no reports in Japan describe, in detail, the types of antihypertensive drugs used to treat hypertension in cats or its underlying causes. Therefore, we aimed to investigate the use of antihypertensive drugs in domestic cats with hypertension in Japan, the causes of hypertension, and the vital prognosis of these patients. In the present survey, we found that amlodipine was used alone (60/80 cats) or concomitantly (20/80 cats) in all cat patients with hypertension in Japan. We also determined that blood pressure measurements were not yet routinely performed on cats at veterinary clinics in Japan. Furthermore, we have new information suggesting that amlodipine administration in cats with hypertension, which lowers systolic arterial pressure levels to within the normal range (<140 mmHg), may have a negative impact on their survival. Routine blood pressure measurements for cats during their regular health checkups can help identify hypertension, and proper interpretation of blood pressure readings can facilitate suitable treatment measures.

Quantitative studies on B-mode ultrasound and point shear wave elastography of kidneys in nonazotemic dogs

Renal diseases in dogs can be diagnosed effectively using B-mode ultrasound. Point shear wave elastography (pSWE) has demonstrated usefulness in diagnosing renal diseases in human medicine. However, its application in veterinary medicine is in its nascent stage. It was hypothesized that establishing pSWE reference values in nonazotemic dogs would prove valuable in differentiating renal diseases. In light of this, a single-center, quantitative study with an objective to normalize B-mode ultrasound parameters and pSWE values of the kidney in nonazotemic dogs was conducted. A total of 198 animals presented with clinical signs of anorexia, vomiting, weight loss, and dehydration were enrolled in the study spanning 2 years. Among them, 52 nonazotemic dogs were included as subjects for the study. B-mode ultrasound quantitative parameters, including length (L), breadth (B), height (H), cortical thickness (RCT), and medulla thickness (RMT) of the kidneys, as well as the diameter of the aorta (Ao), were normalized. Additionally, calculated parameters such as L:Ao, B:Ao, H:Ao, RCT:Ao, and corticomedullary ratios were worked out. Point shear wave elastography values were obtained from the cranial and caudal poles of renal cortices using ElastPQ stiffness software. The pSWE values of kidneys in nonazotemic dogs were normalized. The mean ± standard error values were 1.04 ± 0.08 m/s (95% confidence interval: 0.88-1.19 m/s) and 4.18 ± 0.62 kPa (95% confidence interval: 2.93-5.42 kPa). In conclusion, B-mode ultrasound quantitative parameters, ratios, and pSWE values were normalized in nonazotemic dogs, which may prove valuable in differentiating renal pathologies in canine patients.

Symmetric dimethylarginine correlates with the urea, creatinine, potassium, and clinical scores in feline urethral obstructions

BACKGROUND

A urethral obstruction (UO) is an emergency commonly observed in male cats, which can result in significant clinical and laboratory alterations, leading to complications and death.

OBJECTIVES

This study aimed to correlate symmetric dimethylarginine (SDMA) with the urea, creatinine, potassium, and bicarbonate levels in cats with UO. In addition, the correlation between clinical score and time of obstruction was evaluated.

METHODS

Thirty male cats were selected and allocated into a control group (CG, n = 13) and an obstruction group (OG, n = 17). The laboratory analyses were conducted before treatment (M0) and at different times after treatment (12 h [M12], 24 h [M24], and 48 h [M48]). Correlations were established between SDMA and creatinine, urea, bicarbonate, potassium, time of obstruction, and the clinical score.

RESULTS

A strong correlation (r > 0.6) was observed between SDMA and creatinine, urea, and potassium in the OG. Furthermore, there was substantial agreement (kappa value) between SDMA and creatinine at M24. A higher clinical score was associated with a longer time of obstruction. In the OG, at M48, the SDMA and creatinine levels were 50% and 41.2% higher, respectively.

CONCLUSIONS

A correlation was observed between SDMA and creatinine in obstructed cats, and significant agreement between these values was observed 24 h after the unblocking treatment. A correlation among SDMA, urea, and potassium was observed. Approximately 9% more cats continued to have elevated SDMA levels after 48 h of treatment compared to creatinine. This suggests a slightly lower sensitivity of the latter biomarker but does not exclude the possibility of congruent and normalized values after a longer evaluation period.

Serum symmetric dimethylarginine in older dogs: Reference interval and comparison of a gold standard method with the ELISA

BACKGROUND

Serum symmetric dimethylarginine (SDMA) is used to screen for renal dysfunction in dogs. The gold standard technique for measuring SDMA, liquid chromatography-tandem mass spectrometry (LC-MS/MS) is not widely available. Age-specific reference intervals for SDMA in older dogs are lacking.

OBJECTIVES

Prospective study in older dogs to validate a commercially available LC-MS/MS method for SDMA, compare SDMA concentrations with concentrations measured using ELISA and obtain a reference interval (RI) for older dogs using both methods.

ANIMALS

Client-owned older dogs undergoing health screening.

METHODS

The LC-MS/MS method was analytically validated (limit of detection, precision, and linearity). Serum was sent cooled overnight for ELISA or was frozen at -80°C until batch analysis using LC-MS/MS. Results of LC-MS/MS and ELISA were compared and RIs for older dogs were calculated according to international guidelines.

RESULTS

The LC-MS/MS method showed good linearity (r2  = .99) and precision (coefficient of variation <10%), with a laboratory RI between 8.0 and 14.0 μg/dL. Paired measurements were available from 118 different dogs. Median SDMA concentration were 9.4 (range, 5.0-21.2) using LC-MS/MS and 12.0 (range, 5.0-22.0) μg/dL using ELISA. Both methods significantly differed with a mean difference of 2.2 μg/dL. The RI for older dogs for LC-MS/MS was 4.4-15.0 μg/dL, and for ELISA was 6.4-17.4 μg/dL.

CONCLUSIONS AND CLINICAL IMPORTANCE

The ELISA provided significantly higher SDMA concentrations compared to the validated LC-MS/MS method, indicating the need for device- or assay-specific RI. The obtained age-specific RI for SDMA is considerably higher in older dogs compared to the general laboratory RI.

Novel renal injury markers in dogs with ehrlichiosis

Canine monocytic ehrlichiosis (CME) has been observed to impact renal function. Currently, the recognition of acute kidney injury is through the nonspecific biomarker serum creatinine (sCr). Novel markers of renal injury such as urinary clusterin (uClust) and urinary cystatin B (uCysB) may increase our understanding of the relationship between ehrlichiosis and renal cellular injury. The aim of this study was to evaluate novel renal injury biomarkers in dogs with acute CME. Twenty healthy dogs were enrolled in the control group (CG), and 16 dogs naturally infected with Ehrlichia canis were included in the Ehrlichia Group (EG). All dogs were followed for 45 days. EG dogs were treated with doxycycline twice daily for the first 30 days. Urine and serum were collected at: 0, 0.5, 1, 15, 30, and 45 days after start of treatment. Urine concentrations of uClust and uCysB were determined using a research ELISA immunoassay. A linear mixed model was used to estimate population mean of renal injury markers with patient as the random effect, and day and treatment as fixed effects. EG was observed to have higher uClust values compared to CG (estimated population mean EG: 213 ng/dL vs. CG: 84 ng/dL, P < 0.001). EG was observed to have higher uCysB values compared to CG (estimated population mean EG: 248 ng/dL vs. CG: 38 ng/dL, P < 0.001). Increases in uCysB and uClust suggest the presence of renal injury and a possible mechanism for the observed predisposition to chronic kidney disease in dogs with ehrlichiosis.

Comparison of serum creatinine, point-of-care symmetric dimethylarginine and renal imaging with glomerular filtration rate measured by renal scintigraphy in healthy and early chronic kidney diseased cats

The aim of this study was to evaluate routinely used tests to diagnose cats in early stages of chronic kidney disease (CKD) and to describe a model for evaluating these variables simultaneously. Apparently healthy cats were screened using serum creatinine (sCr), point-of-care symmetric dimethylarginine (POC SDMA), urinalysis, urine protein/creatinine ratio (UPC) and imaging evaluation. Those parameters were compared to glomerular filtration rate (GFR) assessed by renal scintigraphy. Forty-four cats were included and consisted of 14 (31.8%) healthy cats (absence of abnormalities in renal morphology and sCr less than 1.6 mg/dL), 20 (45.5%) cats classified as CKD I (presence of abnormalities in renal morphology and sCr less than 1.6 mg/dL) and ten (22.7%) as CKD II (sCr equal to or greater than 1.6 mg/dL, with or without abnormalities in renal morphology). A large number (40.9%) of apparently healthy cats presented reduction in GFR, which included half of CKD I patients. Point-of-care SDMA was not a good predictor for decreased GFR, nor was it correlated with the variables GFR and sCr. Glomerular filtration rate was significantly lower in CKD I and II groups in comparison with healthy cats, but there was no significant difference between the CKD I and II groups. Multivariate logistic regression model identified three variables that affected the odds of a cat having decreased GFR (< 2.5 mL/min/kg): sCr (OR = 18.3; p = 0.019; CI = 1.6-207.2), and the ultrasonographic findings 'reduced corticomedullary definition' (OR = 19.9; p = 0.022; CI = 1.6-254.0) and 'irregular contour' (OR = 65.6; p = 0.003; CI = 4.2-1038.2). Renal ultrasonography evaluation should always be considered for screening early CKD in apparently healthy cats.

Determination of mitochondrial functions and damage in kidney in female LeeSung minipigs with a high-fat diet-induced obesity

The purpose of this study was to investigate the nexus between mitochondrial function and kidney injury by using a dietary-induced obese minipig model. Female Lee-Sung minipigs feeding a high-fat diet (HFD) for 6 months exhibited obesity, hyperglycaemia and dyslipidemia. HFD elevated the levels of plasma biomarkers related to renal injury, including symmetric dimethylarginine, creatinine and urea nitrogen. An extensive structural change in tubules and glomeruli was observed in HFD-fed pigs. A great amount of triacylglycerol was accumulated in HFD kidney compared to control kidney, whereas a reduction of ATP level and antioxidant capacity were exhibited in HFD kidney. Moreover, HFD altered the expressions of mitochondrial-related protein in renal cortex. To conclude, long-term HFD feeding to Lee-Sung minipigs induced obesity and kidney injury accompanied by abnormal mitochondrial functions in the renal cortex, suggesting an interrelationship with renal disease progression.

Clinical management of feline chronic kidney disease in Portugal: a questionnaire-based study

OBJECTIVES

The aim of the study was to characterise the clinical management of feline chronic kidney disease (CKD) by veterinary practitioners in Portugal.

METHODS

A questionnaire-based study was designed to be completed by all veterinarians who had diagnosed and treated at least one case of feline CKD in the previous year.

RESULTS

A total of 409 veterinary practitioners responded to the questionnaire, with approximately half of them diagnosing 2-5 cases of feline CKD per month (n = 219, 53.5%). Although a high proportion of these reported using the guidelines published by the International Renal Interest Society (n = 379, 92.7%), only 19.1% (n = 78) systematically performed systolic blood pressure (SBP) measurements in all of their patients. A renal diet was advised by almost all respondents (n = 406, 99.3%), but 36.9% (n = 150) of them considered that it represented less than 75% of the daily food intake for most of their patients. This dietary intervention was often prescribed regardless of stage (n = 298, 73.4%) and without a proper gradual diet transition. Appetite stimulants were frequently prescribed (n = 366, 89.5%), as well as a calcium channel blocker (n = 171, 41.8%) and an angiotensin-converting enzyme inhibitor (n = 245, 59.9%) to control systemic hypertension and proteinuria, respectively. Prescription of a phosphate binder was also common (n = 311, 76.0%). Regarding monitoring, 70.9% (n = 290) recommended that stable patients be reassessed every 2-3 months or more frequently, but only 35.7% (n = 146) were able to comply with this periodicity due to owners' constraints.

CONCLUSIONS AND RELEVANCE

The findings showed that although most survey respondents are aware of international guidelines for the clinical management of cats with CKD, the SBP measurement still needs to be more systematic to allow proper substaging and detection of systemic hypertension. The monitoring frequency was lower than recommended. Furthermore, the introduction of a renal therapeutic diet should be refined to improve its acceptance rate.

Plasma Neurofilament Light Chains as Blood-Based Biomarkers for Early Diagnosis of Canine Cognitive Dysfunction Syndrome

The number of elderly dogs is increasing significantly worldwide, and many elderly dogs develop canine cognitive dysfunction syndrome (CCDS). CCDS is the canine analog of Alzheimer's disease (AD) in humans. It is very important to develop techniques for detecting CDDS in dogs. Thus, we used the detection of neurofilament light chains (NfL) in plasma as a blood-based biomarker for the early diagnosis of canine Alzheimer's disease using immunomagnetic reduction (IMR) technology by immobilizing NfL antibodies on magnetic nanoparticles. According to the 50-point CCDS rating scale, we divided 36 dogs into 15 with CCDS and 21 without the disease. The results of our IMR assay showed that the plasma NfL levels of dogs with CCDS were significantly increased compared to normal dogs (p < 0.01). By plasma biochemical analysis, we further confirmed that the liver and renal dysfunction biomarkers of dogs with CCDS were significantly elevated compared to normal dogs (p < 0.01-0.05). On the basis of our preliminary study, we propose that IMR technology could be an ideal biosensor for detecting plasma NfL for the early diagnosis of CCDS.

Effect of storage temperature and time on measurement of serum symmetric dimethylarginine concentration using point-of-care and commercial laboratory analyzers in cats and dogs

BACKGROUND

Stability of serum symmetric dimethylarginine (sSDMA) during short- and long-term storage has not been assessed for the immunoassay of the Point-of-Care IDEXX Catalyst DX (POC) analyzer and the Enzyme Multiplied Immunoassay Technique of IDEXX commercial laboratory (CL). Also, the agreement between both analyzers is questioned.

OBJECTIVES

To determine (a) the effect of storage time and temperature on sSDMA measured by POC and CL; (b) the agreement between sSDMA measured by POC and CL; and (c) the imprecision of the POC.

ANIMALS

Serum of cats (n = 17) and dogs (n = 18) with a range of SDMA concentrations (6 to >100 μg/dL).

METHODS

Based on an equivalence trial with predefined equivalence range (-3.0 to +3.0 μg/dL) and using T0 as baseline, stability was evaluated after 24 hours at 22°C and 4°C (POC); after 7 days at 4°C (POC and CL) and after 10 and 24 months at -24°C and -80°C (CL). Bland-Altman plots enabled method comparison. Imprecision of the POC was assessed by duplicate sSDMA measurements at T0.

RESULTS

The POC analyzer produced equivalent sSDMA measurements if samples were stored for 24 hours at 4°C (95% confidence interval [CI]: -2.5-2.0 μg/dL), but not when stored for 24 hours at room temperature (RT; 95% CI: -4.1 to 0.5 μg/dL) or after 7 days at 4°C (95% CI: -3.6-1.0 μg/dL). The CL analyzer was less affected by preanalytical variation with clinically similar results obtained when samples were stored for 7 days at 4°C (95% CI: -2.2 to 2.4 μg/dL) and for at least 24 months at -24°C (95% CI: -1.7 to 2.9 μg/dL) and -80°C (95% CI: -1.5 to 3 μg/dL). A relevant mean difference of -2.3 μg/dL between both analyzers was found. Duplicate POC measurements were equivalent (95% CI: -2.6 to 2.0 μg/dL).

CONCLUSIONS

Delayed analysis may significantly change sSDMA depending on storage and measurement conditions. Interchangeable use of assays should be done with caution because analytical variation could be interpreted as clinically relevant change.

Do post-surgical multiresistant urinary infections occur in horses? Case of unilateral pyelonephritis caused by extended-spectrum beta-lactamase-producing bacteria as a complication of cystotomy

Pyelonephritis is a serious condition that is rarely described in horses. In contrast, urinary tract infections are common in humans and small animals, and multi-drug-resistant urinary infections are an emerging threat. In this report, we describe a horse with unilateral pyelonephritis caused by extended-spectrum beta-lactamase-producing bacteria belonging to the Enterobacter cloacae complex. [Correction added on 9 August 2023, after first online publication: The preceding sentence was corrected.] An 11-year-old Swedish warmblood gelding was diagnosed with a cystolith and a cystotomy through an open left para-inguinal approach was performed. Seven days after surgery the horse presented with pyrexia, dullness and colic. Diagnostic testing and renal transabdominal ultrasonography confirmed the presence of a right-sided pyelonephritis. Culture and antimicrobial susceptibility testing revealed a pure growth of extended-spectrum beta-lactamases-producing E. cloacae complex bacteria with resistance against beta-lactams, aminoglycoside and trimethoprim-sulphonamide classes. Treatment included prolonged oral antimicrobials according to susceptibility testing results (enrofloxacin), judicious use of non-steroidal anti-inflammatory drugs, fluid therapy and gastric ulcer prophylaxis. The horse recovered successfully and is currently in good health (follow-up of 5 years). Once the infection resolved, unilateral renal scarring occurred. Multidrug-resistant upper-urinary infections occur in horses and should be considered in a post-surgical patient that develops fever. Early diagnosis, urine bacterial culturing and antimicrobial susceptibility testing were crucial in this case to successful management.

Evaluation of renal values during treatment for heartworm disease in 27 client-owned dogs

BACKGROUND

Canine heartworm disease (CHD) caused by Dirofilaria immitis remains a common preventable disease with increasing incidence in some parts of the USA. The treatment guidelines of the American Heartworm Society (AHS) currently recommend monthly macrocyclic lactone administration, 28 days of doxycycline given orally every 12 h and three injections of melarsomine dihydrochloride (1 injection on day 2 of treatment followed 30 days later by 2 injections 24 h apart). Minocycline has also been utilized when doxycycline is unavailable. The systemic effects of CHD, which particularly impact cardiac and renal function, have been described, with infected dogs often experiencing renal damage characterized by an increase in serum concentrations of renal biomarkers. Although the AHS treatment protocol for CHD has been shown to be safe and effective in most cases, the potential for complications remains. No study as of yet has evaluated changes in symmetric dimethylarginine (SDMA), a sensitive marker of renal function, during treatment for CHD. The purpose of the present study was to evaluate renal function in dogs by measuring serum creatinine and SDMA concentrations during the adulticide treatment period.

METHODS

Serum creatinine and SDMA concentrations were measured in 27 client-owned dogs affected by CHD at the following time points: prior to starting doxycycline or minocycline therapy (baseline), during doxycycline or minocycline therapy (interim), at the time of the first dose of melarsomine (first dose), at the time of the second dose of melarsomine (second dose) and at the dog's follow-up visit after treatment, occurring between 1 and 6 months after completion of therapy (post-treatment). Concentrations of creatinine and SDMA were compared between time points using a mixed effects linear model.

RESULTS

Mean SDMA concentrations following the second dose of melarsomine were significantly lower (-1.80 ug/dL, t-test, df = 99.067, t = -2.694, P-Value = 0.00829) than baseline concentrations. There were no other statistically significant differences in the concentration of either biomarker between the baseline and the other time points in CHD dogs undergoing treatment.

CONCLUSIONS

The results suggest that the current AHS protocol may not have a substantial impact on renal function.

Comparison of Three Different Diagnostic Assays for Fibroblast Growth Factor-23 (FGF-23) Measurements in Cats: A Pilot Study

Fibroblast growth factor-23 (FGF-23) is a phosphaturic hormone used to monitor chronic kidney disease (CKD) in humans. The aim of this pilot study was to compare three diagnostic assays and to assess how the results correlate with parameters of renal dysfunction in cats. Four groups of 10 cats each were formed retrospectively according to creatinine, based on IRIS staging. FGF-23 was measured using two different ELISAs (MyBioSource and Kainos ELISA FGF-23 Kit) and an automated assay on the DiaSorin Liaison platform. Measurements were performed in 40 cats. Spearman's rank correlation coefficient showed a strong correlation between the Kainos and DiaSorin assays (ρ = 0.742/p < 0.001) and a low correlation (ρ = 0.443/p = 0.005) between the Kainos and MyBioSource assays. The measurements with the Kainos assay strongly correlated with urea (ρ = 0.835/p < 0.001) and creatinine (ρ = 0.764/p < 0.001), and moderately correlated with SDMA (ρ = 0.580/p < 0.001) and phosphorus (ρ = 0.532/p < 0.001). The results of the MyBioSource and DiaSorin assays only showed a moderate correlation with urea (ρ = 0.624/0.572) and creatinine (ρ = 0.622/0.510) concentrations (p = 0.001 each). The Kainos assay showed the strongest correlation (ρ = 0.806) with the various creatinine concentrations according to the IRIS, followed by the MyBioSource (ρ = 0.663/p < 0.001) and DiaSorin assays (ρ = 0.580/p < 0.001). Overall, the Kainos assay demonstrated the best correlations with both biomarkers and various creatinine concentrations according to the IRIS. Individual assay-based reference values should be established to make a reliable interpretation of FGF-23 levels possible to diagnose or monitor feline CKD.

Changes in symmetric dimethylarginine and glomerular filtration rates in hyperthyroid cats undergoing radioiodine therapy

OBJECTIVES

The aims of this study were to evaluate concentrations of symmetric dimethylarginine (SDMA) in hyperthyroid cats before and after radioiodine treatment, and to compare results with other variables used to assess kidney function in cats (creatinine, urine specific gravity [USG] and glomerular filtration rate [GFR] measured by renal scintigraphy).

METHODS

Thirteen cats diagnosed with hyperthyroidism based on clinical signs and increased serum total thyroxine (TT4) were included in this prospective study. Study design included physical examination, complete blood count, serum chemistry, TT4, urinalysis and SDMA before treatment (T0) and at 1 month (T1) and 3 months post-treatment (T3). GFR was quantified by renal scintigraphy at T0 and T3.

RESULTS

Median GFR decreased significantly from baseline (3.18 ml/kg/min; range 1.35-4.87) at T3 (2.22 ml/kg/min; range 1.81-3.42 [P = 0.005]). While median creatinine and serum urea nitrogen increased post-treatment (creatinine: T0 = 0.8 mg/dl [range 0.4-1.1], T1 = 1.3 mg/dl [range 0.9-2]; T3 = 1.65 mg/dl [range 0.8-2.8]; P <0.001; serum urea nitrogen: T0 = 23 mg/dl [range 15-26]; T1 = 27 mg/dl [range 20-40]; T3 = 27.5 mg/dl [range 20-36]; P <0.001), SDMA and USG did not change significantly (SDMA: T0 = 11 µg/dl [range 7-15]; T1 = 12 µg/dl [range 6-16]; T3 = 10.5 µg/dl [range 8-21]; P = 0.789; USG: T0 = 1.030 [range 1.011-1.059]; T1 = 1.035 [range 1.012-1.044]; T3 = 1.030 [range 1.007-1.055]; P = 0.792).

CONCLUSIONS AND RELEVANCE

Our data suggest that factors other than GFR may affect serum SDMA in hyperthyroid cats and that SDMA does not offer an advantage over other biomarkers traditionally used to predict changes in renal function following radioiodine therapy.

Efficacy of domperidone plus renal diet in slowing the progression of chronic kidney disease in dogs with leishmaniosis

BACKGROUND

Chronic kidney disease (CKD) represents the main cause of mortality in dogs with leishmaniosis. Domperidone has recently been reported to improve kidney function in leishmaniotic dogs affected by CKD. Serum symmetric dimethylarginine (sSDMA) has also been shown to be a useful biomarker for earlier detection of decreased kidney function when compared to serum creatinine (sCr). This study aimed to assess the efficacy of domperidone plus renal diet in slowing the progression of nephropathy in leishmaniotic dogs with CKD, evaluating sSDMA and sCr as markers of kidney function.

METHODS

This study was a therapeutic, prospective, randomized, controlled, 11-month-long field trial. Dogs were recruited if classified as "exposed" to or "infected" with Leishmania infantum and affected by CKD at early stages. After enrolment (T0), dogs were randomized into groups T (treatment) and C (control). All dogs were fed a renal diet and then followed up at 90 (T1), 210 (T2), and 330 (T3) days after inclusion in the study. At T1 and T2, dogs in group T received an oral suspension of domperidone (1 ml/10 kg once a day for up to 28 days).

RESULTS

Twenty-two dogs (i.e., n = 12 in group T and n = 10 in group C) completed the study. At T0, the entire population of enrolled dogs presented a mean sSDMA value of 16.5 ± 3.4 μg/dl. At T1 (i.e., after 3 months of renal diet), sSDMA was significantly decreased in both groups, with an sSDMA of 13.1 ± 4.4 μg/dl for the entire population involved. From T1 to T3, sSDMA gradually increased in group C, while remaining stable in group T, which continued to show a significantly lower value of sSDMA at T3 than at T0. Regarding sCr, at T0 and T1, the mean values of the entire population of dogs were 1.1 ± 0.3 and 1.0 ± 0.4 mg/dl, respectively, with no statistical differences between groups T and C. In group T, sCr decreased significantly from T0 to T1, while returning at T3 to values similar to T0.

CONCLUSIONS

In this study, domperidone plus renal diet reduced the progression of kidney disease in leishmaniotic dogs affected by CKD.

Endogenous markers of kidney function and renal drug clearance processes of filtration, secretion, and reabsorption

The kidneys are responsible for maintaining physiologic homeostasis. The kidneys clear a variety of drugs and other substances through passive (filtration) and active processes that utilize transport proteins. Renal clearance is comprised of the processes of glomerular filtration, tubular secretion, and tubular reabsorption. Endogenous biomarkers, such as creatinine and cystatin C, are routinely used to estimate renal clearance. Understanding the contributing components of renal function and clearance, through the use of biomarkers, is necessary in elucidating the renal pharmacology of drugs and other substances. While exogenous markers of kidney function have been known for decades, several complexities have limited their usage. Several endogenous markers are being evaluated and hold promise to elucidate the individual components of kidney function that represent filtration, secretion, and reabsorption.

Hyperthyroid cats and their kidneys: a literature review

Hyperthyroidism and chronic kidney disease (CKD) are common diseases of geriatric cats, and often occur concurrently. Thus, a thorough understanding of the influence of thyroid function on renal function is of significant value for all feline practitioners. Among other effects, hyperthyroidism causes protein catabolism and increases renal blood flow and glomerular filtration rate (GFR). These effects render traditional renal markers insensitive for the detection of CKD in cats with uncontrolled hyperthyroidism. Furthermore, the development of iatrogenic hypothyroidism with over treatment of hyperthyroidism can be detrimental to renal function and may negatively affect long-term survival. This review discusses important diagnostic considerations of feline hyperthyroidism, as well as key treatment modalities, with an emphasis on the use of radioiodine and the importance of post treatment monitoring of thyroid and renal parameters. In Australia, a common curative treatment for cats with benign hyperthyroidism (i.e. thyroid hyperplasia or adenoma) is a fixed dose of orally administered radioiodine, regardless of the serum total thyroxine concentration at the time of diagnosis. This review discusses the long term outcomes of this standard of care in comparison with current, relevant research literature from around the world. Finally, this review explores the use of symmetric dimethylarginine (SDMA) in assessing renal function before and after treatment in hyperthyroid cats. SDMA correlates well with GFR and creatinine in non-hyperthyroid cats, but our understanding of its performance in hyperthyroid cats remains in its infancy.

Serum concentrations of leptin and adiponectin in dogs with chronic kidney disease

BACKGROUND

An imbalance in adipokines is associated with the progression of chronic kidney disease (CKD) in humans. However, alterations in adipokines in dogs with CKD remain unclear.

OBJECTIVES

To examine whether adipokine concentrations in serum differ between healthy dogs and dogs with CKD and to determine the correlation between serum adipokine concentrations and CKD severity in dogs.

ANIMALS

Twenty dogs with CKD and 10 healthy dogs.

METHODS

In this cross-sectional study, serum concentrations of leptin, adiponectin, interleukin (IL)-6, IL-10, IL-18, and tumor necrosis factor (TNF)-α were measured in healthy dogs and dogs with CKD, which were classified according to the International Renal Interest Society guidelines.

RESULTS

Serum leptin concentrations were positively correlated with systolic arterial blood pressure (r = .41), creatinine concentrations (r = .39), and symmetric dimethylarginine concentrations (r = .73). Serum adiponectin concentrations (median [range]) in CKD dogs with borderline or non-proteinuric (20.25 [14.9-45.8] ng/mL) were significantly higher than those in proteinuric CKD dogs (13.95 [6.4-22.1] ng/mL; P = .01). Serum IL-6 (median [range]; 43.27 [24.30-537.30] vs 25.63 [6.83-61.03] pg/mL; P = .02), IL-18 (median [range]; 25.98 [11.52-280.55] vs 10.77 [3.53-38.45] pg/mL; P = .01), and TNF-α (median [range]) concentrations (11.44 [8.54-38.45] vs 6.105 [3.97-30.68] pg/mL; P = .02) were significantly different between proteinuric and borderline or non-proteinuric CKD dogs.

CONCLUSIONS AND CLINICAL IMPORTANCE

leptin and adiponectin concentrations in serum might be associated with severity of CKD and proteinuria in dogs with CKD, respectively.

Blood concentration of symmetric dimethylarginine correlates with kidney damage as assessed with a proposed histologic grading system for chronic kidney disease in tigers (Panthera tigris)

OBJECTIVE

To determine the utility of blood symmetric dimethylarginine (SDMA) concentration measurement as a diagnostic tool for chronic kidney disease (CKD) in tigers (Panthera tigris) by comparing results for SDMA with those for traditional renal biomarkers and investigating correlations between these biomarkers and histopathologic kidney changes in tigers with CKD.

SAMPLE

Blood, urine, and kidney samples from 35 tigers with CKD from 2 sanctuaries.

PROCEDURES

Blood (serum or plasma) and urine samples were collected antemortem. Necropsy, including gross and histologic assessment, was performed for tigers that died or were euthanized for quality-of-life reasons. Results for CKD biomarkers in blood (BUN, creatinine, phosphorus, and SDMA concentrations) and urine (protein concentration, urine protein-to-creatinine ratio, and urine specific gravity) were evaluated for correlation with histologic kidney damage scored with an objective grading scale defined by percentage of inflammation, fibrosis, and tubular atrophy.

RESULTS

Symmetric dimethylarginine had the strongest significant correlation (ρ = 0.667) with histologic kidney damage score, followed by urine specific gravity (ρ = -0.639), blood creatinine concentration (ρ = 0.624), and BUN (ρ = 0.588). No significant correlation with kidney score was identified for blood phosphorus concentration, urine protein concentration, or the urine protein-to-creatinine ratio.

CLINICAL RELEVANCE

We recommend SDMA be prioritized as a renal biomarker in tigers, with SDMA results considered in addition to those of other traditional renal biomarkers when assessing kidney function in tigers. Additionally, the grading scale we developed could be replicated across patients and pathologists for more consistent postmortem assessment of CKD in tigers.

Renal biomarkers in cats: A review of the current status in chronic kidney disease

Serum creatinine concentration, the classical biomarker of chronic kidney disease (CKD) in cats, has important limitations that decrease its value as a biomarker of early CKD. Recently, serum symmetric dimethylarginine concentration was introduced as a novel glomerular filtration rate biomarker for the early detection of CKD in cats. However, data on its specificity are still limited. The limitations of conventional biomarkers and the desire for early therapeutic intervention in cats with CKD to improve outcomes have prompted the discovery and validation of novel renal biomarkers to detect glomerular or tubular dysfunction. Changes in the serum or urinary concentrations of these biomarkers may indicate early kidney damage or predict the progression of kidney before changes in conventional biomarkers are detectable. This review summarizes current knowledge on renal biomarkers in CKD in cats, a field that has progressed substantially over the last 5 years.

Symmetrical Dimethylarginine as a Diagnostic Parameter in Hermann's Tortoises (Testudo hermanni)

Background

Despite improvements in habitational conditions, kidney disease is relatively common in tortoises.

Objectives

Purpose of this study was the establishment of Symmetrical dimethylarginine (SDMA) reference values for clinically healthy Hermann's Tortoises.

Animals

Clinically healthy Hermann's Tortoises (n = 131) were included in the period from October 2017 to September 2019.

Methods

Creatinine and other biomarkers were tested at IDEXX Laboratories, Germany using residual blood samples from Hermann's tortoises. SDMA was measured with the IDEXX test and verified by liquid chromatography-mass spectrometry at IDEXX Laboratories, USA.

Results

SDMA values ranged from 1 to 21 μg/dl (n = 131) for the IDEXX SDMA Test and SDMA values ranged from 1 to 17 μg/dl (n = 82) for LC-MS. For the comparison of the two measuring systems, the following results were obtained R 2 = 0.75 (p < 0.001).

Conclusion and Clinical Importance

SDMA can be measured in Hermann's Tortoises and the reference values range in clinically healthy animals is comparable to that of dogs and cats.

Short course of immune-suppressive doses of prednisolone, evaluated through a prospective double-masked placebo-controlled clinical trial in healthy Beagles, is associated with sustained modifications in renal, hydration, and electrolytic status

OBJECTIVE

To investigate the effects and duration of orally administered prednisolone on renal function evaluated by glomerular filtration rate (GFR) determination and creatinine (Cr) and symmetric dimethylarginine (SDMA) concentrations as well as on urinalysis, electrolytes, and hydric status in healthy dogs.

ANIMALS

14 healthy Beagles.

PROCEDURES

In this prospective double-masked placebo-controlled study, dogs were randomized after baseline evaluation to receive a 7-day course of either prednisolone (1.5 to 2.0 mg/kg, PO, q 12 h) or a placebo. A repeated-measure design was performed, each dog participating in 4 successive sampling sessions. Clinical data, systolic blood pressure, CBC, and biochemical analyses including serum SDMA concentration, GFR determination, urine output quantification, and complete urinalysis were performed for all dogs the day before (D0) and at the end of steroid administration (D7) as well as 2 weeks (D21) and 4 weeks (D35) after the end of treatment.

RESULTS

At D7, when compared with baseline, GFR increased significantly in treated dogs, whereas creatinine and SDMA concentrations decreased significantly. GFR and Cr but not SDMA modifications persisted significantly at D21. None of the variables differed significantly from baseline at D35. The OR of presenting an albumin band on urine electrophoresis was 2.4 times as high in treated versus control dogs (OR, 36; 95% CI, 1.8 to 719.4; P = 0.02).

CLINICAL RELEVANCE

A short-term course of immune-suppressive prednisolone treatment in healthy dogs leads to a sustained but reversible renal hyperfiltration state. Modification in electrolytic variables can affect the clinical interpretation of blood work in such patients.

Evaluation of symmetric dimethylarginine and Doppler ultrasonography in the diagnosis of gentamicin-induced acute kidney injury in dogs

Acute kidney injury is a common problem in dogs and is associated with significant morbidity and mortality. So, the present study aimed to evaluate symmetric dimethylarginine (SDMA) and Doppler ultrasonography including resistive index (RI) in the diagnosis of acute kidney injury in dogs. Ten healthy mongrel dogs were injected with gentamicin sulfate 10% at the dose of 30 mg/kg body weight daily for 10 days for induction of acute kidney injury. Clinical, biochemical, ultrasonographic, and Doppler ultrasonographic examinations and urinalysis were performed for all dogs on 0 day before induction, on the 5th day, and on the 10th day of induction. The results of the current study showed significant increase in plasma level of SDMA, serum urea, creatinine, phosphorus, and potassium and a significant decrease in serum sodium, calcium, and chloride on the 5th day and 10th day of induction, and there was an increase in renal cortical echogenicity of the right and left kidney compared to adjacent liver and spleen, respectively. RI value showed a significant increase on the 5th day and 10th day of induction. The present study showed that SDMA is a sensitive and promising biomarker for diagnosis of acute kidney injury in dogs compared to routine biomarkers; also, the RI of Doppler ultrasonography is useful for early identifying acute kidney injury when the only observable change is an increase in cortical echogenicity.

Symmetric dimethylarginine concentrations in healthy neonatal foals and mares

BACKGROUND

Symmetric dimethylarginine (SDMA) is a renal biomarker correlated with glomerular filtration rate (GFR).

OBJECTIVES

Describe changes in SDMA in clinically healthy foals and their mares during the first month postfoaling.

ANIMALS

Convenience sampling of healthy periparturient Thoroughbred mares and their full-term foals from a population of client-owned horses.

METHODS

Serum and EDTA whole blood samples were collected from mares in their last month of pregnancy and then from mares and foals at approximately <12 hours, 48 hours, 7 days, and 30 days postbirth. Samples were processed at a commercial reference laboratory for CBC and serum biochemistry, including SDMA concentrations.

RESULTS

A total of 125 foals and 104 mares were included. Upper limits for SDMA concentrations in foals were above the adult horse reference interval for the first 20 or more days of life. Median SDMA concentrations decreased from 70 μg/dL (range, 7-100 μg/dL) to 18 μg/dL (range, 6-27 μg/dL) during the first 3 to 4 weeks of life. At birth, the SDMA concentration reference range was established as 0 to 100 μg/dL (upper limit of the assay); 0 to 85 μg/dL for 1 to 4 days old, 0 to 36 μg/dL for 5 to 10 days old, and 0 to 24 μg/dL for 20 to 30 days old. The upper reference limits for SDMA concentrations in mares did not differ from the general reference interval for adult horses. No correlation was identified between mare and foal SDMA concentrations (ρ = .06, P = .58).

CONCLUSIONS AND CLINICAL IMPORTANCE

Foal SDMA concentrations remained higher than the upper limit of the adult reference range and foals require a different reference range dependent on age.

Use of Levetiracetam in Epileptic Dogs with Chronic Kidney Disease: A Retrospective Study

In human medicine, doses of levetiracetam (LEV) are individualized for patients with epilepsy, depending on the status of the patient’s renal function. However, there are not reports on the individualized dosing of LEV for small animals. The aim of this study is to investigate whether a dose adjustment of LEV is needed in dogs with chronic kidney disease (CKD). Patient databases were searched, and 37 dogs with seizures or epilepsy were retrospectively included in this study. Based on pre-existing CKD, patients were divided into a CKD group (n = 20) and a non-CKD group (n = 17). We collected kidney panels before and after LEV treatment. Side-effects were monitored for 1 month after the start of LEV administration. In the CKD group, more dogs developed adverse effects (85%) than in the non-CKD group (52.94%). After LEV administration, an increase in blood urea nitrogen and/or serum creatinine was more often reported in the CKD group than it was in the non-CKD group. Our data indicate that in dogs with seizures or epilepsy with pre-existing CKD, an LEV dose-adjustment is needed. During LEV treatment, CKD patients should be monitored for side-effects and may require laboratory evaluation of renal function.

USE OF SYMMETRIC DIMETHYLARGININE TO DETECT RENAL LESIONS IN FISH: A PRELIMINARY STUDY IN BROOK TROUT (SALVELINUS FONTINALIS)

Symmetric dimethylarginine (SDMA) is an early marker for renal lesions in mammals. The objectives of this study were 1) to establish a reference interval of SDMA in healthy brook trout, Salvelinus fontinalis (Mitchill, 1814), and 2) to assess its sensibility as a marker of renal pathology. Plasma SDMA was quantified by liquid chromatography-mass spectrometry in 25 adult brook trout, including 20 fish displaying no renal histologic lesions, and five fish displaying chronic nonactive microscopic granulomas. The fish size (P = 0.30) and weight (P = 0.12) were not statistically different among groups, nor were SDMA values (P = 0.22). However, brook trout without microscopic renal lesions tended to have lower SDMA values (no lesions: mean = 24.9 µg/dL; lesions: mean = 31.4 µg/dL). The reference interval (90% confidence interval [90% CI]) for SDMA concentration in brook trout ranged between 10.0 µg/dL (90% CI: 5.4-14.7) and 39.8 µg/dL (90% CI: 34.8-43.9). These values were higher than those previously reported in other vertebrate species. Further research is needed to evaluate the use of SDMA as a marker of renal function in fishes.

Symmetric Dimethylarginine Is a Sensitive Biomarker of Glomerular Injury in Rats

Glomerular filtration rate is the gold-standard method for assessment of renal function but is rarely performed in routine toxicity studies. Standard serum biomarkers of renal function are insensitive and become elevated only with significant loss of organ function. Symmetric dimethylarginine (SDMA) is a ubiquitous analyte that is freely filtered by the glomerulus and can be detected in serum. It has shown utility for the detection of renal injury in dogs and cats in clinical veterinary practice, but the potential utility of SDMA to detect renal injury in preclinical species or toxicity studies has not been thoroughly investigated. We utilized a well-characterized glomerular toxicant, puromycin aminonucleoside, to induce podocyte injury and subsequent proteinuria in young male Sprague-Dawley rats. At the end of 1 or 2 weeks, blood, urine, and kidney tissue were collected for analysis. One week following a single 50 mg/kg dose, urea nitrogen, creatinine, and albumin mean values were within historical control ranges, while SDMA was increased. Glomerular changes in these animals included periodic acid-Schiff positive globules within podocytes, podocyte hypertrophy by light microscopy, and podocyte degeneration with effacement of foot processes by electron microscopy (EM). Taken together, our data indicate that SDMA may be a useful biomarker for early detection of glomerular toxicities in rats.

Serum symmetric dimethylarginine concentration in healthy neonatal Thoroughbred foals

BACKGROUND

Symmetric dimethylarginine (SDMA) is widely used in other species as a marker of renal dysfunction and is considered a more sensitive indicator of glomerular filtration rate than creatinine. Reference ranges are established in healthy adult horses (≤14 μg/dL) and concentrations are increased in horses with acute kidney injury (median 32 μg/dL; range 15-92).

OBJECTIVES

To establish the normal range of SDMA concentrations in neonatal Thoroughbreds.

STUDY DESIGN

Cross-sectional.

METHODS

Blood samples were collected from Thoroughbred foals <36 h old deemed healthy by physical examination. Exclusion criteria included foals from mares undergoing treatment for placentitis and foals that developed clinical disease or died/euthanised <2 weeks from birth. Biochemistry and serum SDMA concentrations were obtained.

RESULTS

Subjects included 120 foals. Median age was 13.5 h (range 1.0-34.0). Median and 95% confidence interval for SDMA concentration was 69.0 µg/dL (63.0, 75.0; range 35.0-376.0). A cut-off value of 168 µg/dL would include 95% of individuals and is therefore suggested. Serum SDMA concentration was correlated with age (R = -.3, P = .003), creatinine concentration (R = .6, P ≤ .001) and urea concentration (R = .3, P = .002).

MAIN LIMITATIONS

Limitations include a small sample size, no consideration of subclinical disease and a short follow-up period.

CONCLUSIONS

In equine neonates, SDMA concentration is higher than in adult horses, older foals and adults with acute kidney injury. Therefore, currently SDMA cannot be used as a marker of renal dysfunction in this age group. Further work is required to assess whether SDMA concentration is increased in neonates with renal disease and, if so, what cut-off should be used.

A longitudinal study of the persistence of increased creatinine and concordance between kidney biomarkers in cats and dogs

Kidney disease causes morbidity and mortality in dogs and cats. Serum creatinine concentration is an important surrogate marker for glomerular filtration rate (GFR). However, it is not always sensitive to small decreases in kidney function. Efforts to identify additional, more sensitive surrogate markers of GFR to improve detection of early kidney disease has led to the use of symmetrical dimethylarginine (SDMA) in veterinary medicine. There is insufficient information about the behavior of creatinine after an increase and the expected behavior of creatinine and SDMA in these cats and dogs. This study assesses the probability of persistence of increases in creatinine and the subsequent behavior of creatinine and SDMA in animals with persistently increased creatinine. For enrollment, three paired SDMA and creatinine concentrations were required: baseline (T0) with creatinine and SDMA at or below the upper reference limit (URL), T1, and T2 0.5-18 months after T1. The study included 4517 cats and 4576 dogs with increased T1 creatinine concentrations and 54,295 cats and 125,403 dogs with T1 creatinine at or below the URL. The probability of a persistently increased creatinine at T2 was approximately 58% for cats and 49% for dogs after a T1 increase. For animals without a T1 increase the probability of increased creatinine at T2 was only 7% for cats and 3% for dogs. For cats and dogs with persistently increased Cr, the probability of an increased SDMA concentration at T1 was 70-75%. By 24 months, that probability rose to 94% for cats and 88% for dogs.

COMPARISON OF BLOOD SYMMETRIC DIMETHYLARGININE AND CREATININE AS ENDOGENOUS MARKERS OF KIDNEY FUNCTION IN CAPTIVE TIGERS (PANTHERA TIGRIS)

Chronic kidney disease (CKD) is a common cause of morbidity and mortality in captive tigers (Panthera tigris). Blood creatinine (Cr) and blood urea nitrogen measurements are inexpensive and common biomarkers used to evaluate renal function. However, several limitations have been reported regarding their sensitivity and interindividual variability. Symmetric dimethylarginine (SDMA) has been suggested to be a more sensitive biomarker that is less affected by extrarenal factors and has a strong correlation with glomerular filtration rate and blood Cr in several species. This project aimed to identify the usefulness of SDMA as an endogenous marker of kidney function in captive tigers. The hypothesis of this study is that increased circulating SDMA is positively associated with increased blood Cr. SDMA and Cr were measured in 65 banked samples (serum and plasma) from 30 individual captive tigers. The samples were collected over a 38-y period and stored at -21°C. SDMA and Cr concentrations were determined using the commercially available SDMA test and enzymatic colorimetric methods, respectively. SDMA had a significant positive association with Cr (for every 1 unit increase of log SDMA, Cr increased by 82%, P = 0.0002). Age and subspecies influenced Cr but not SDMA concentrations. In one animal, blood SDMA increased above the ZIMS reported range. approximately 3.6 mo before Cr increased. SDMA is currently indicated for the diagnosis of CKD in domestic felids and seems also promising in nondomestic felids. Further prospective studies might improve the understanding of the performance of this biomarker.

Renal scintigraphy as an early and efficient method for detecting loss of renal function in a cat

Case summary

A 6-year-old mixed-breed male cat was evaluated for a routine annual health assessment. No alterations on physical examination were observed other than mild pain on palpation of the right kidney. Complete blood count, serum biochemistry (including symmetric dimethylarginine), urinalysis and urine protein:creatinine ratio were within the reference intervals for the species. Abdominal ultrasonography showed the presence of asymmetric kidneys, decreased corticomedullary definition, presence of a cyst on the left kidney and moderate renal pelvis dilatation on the right kidney. Dynamic renal scintigraphy (technetium [^99mTc]-diethylenetriamine pentaacetic acid) revealed a single functioning kidney on the left. Static renal scintigraphy (^99mTc-dimercaptosuccinic acid) exhibited renal activity practically restricted to the left kidney (relative uptake was 99% for the left kidney and 1% for the right kidney). Results of renal scintigraphy showed that the left kidney was compensating for the lack of function of the right one. GFR was 2.17 ml/min/kg, which is considered subclinical renal insufficiency and is in accordance with the case, as the cat was asymptomatic and did not present alterations in laboratory parameters.

Relevance and novel information

Renal scintigraphy was an important tool to determine the loss of renal function in one of the kidneys and mild reduction of global GFR. In this case report, renal scintigraphy proved to be more sensitive in the assessment of renal function than other tests routinely performed.

Evaluation of Chronic Kidney Disease Progression in Dogs With Therapeutic Management of Risk Factors

This research was performed to describe the characteristics of the progression of naturally occurring chronic kidney disease (CKD) in dogs, together with the management of identified risk factors, following the International Renal Interest Society recommendations. Dogs diagnosed and staged with CKD, and with a longitudinal follow-up from the moment of diagnosis of up to a maximum of 730 days, were included. A total of 545 dogs that presented risk factors for the development of CKD were analyzed, out of which 36 met the inclusion criteria. Advanced age was identified in 80.6% of cases. Initiation risk factors were represented by inflammatory/infectious diseases, history of anesthetic-surgical procedures, heart disease, neoplasms, endocrinopathies, and exposure to nephrotoxic drugs. During the follow-up period, progression of CKD was identified in 47.2% of the cases, being more salient in advanced stages. Serum symmetric dimethyl arginine (SDMA) was the only glomerular filtration rate (GFR) marker which displayed differences among studied times during early stages of CKD, associated with the disease progression and decline of renal function. A significant difference between the survival curves in early and advanced CKD stages was observed. The factors related to decreased survival were hyperphosphatemia, anemia, and low body condition score (BCS). No differences were found between the presence of arterial hypertension and renal proteinuria and decreased survival. Furthermore, CKD diagnosis based on the persistent finding of abnormalities in early disease markers, such as serum symmetric dimethyl arginine increase and/or renal proteinuria, and timely therapeutic management of risk factors, allowed for CKD stabilization, reducing progression to advanced stages, and favoring higher survival rates.

Updates on Laboratory Evaluation of Feline Cardiac Diseases

Laboratory tests can be altered in cardiovascular diseases and the investigation of specific tests or biomarkers may provide additional information about myocardial damage. Traditional laboratory tests, such as cell blood count, serum biochemistry, and coagulation, can be useful in investigating patients, but are not specific. However, markers like Troponin and Natriuretic Peptides may possibly furnish further data on myocardium damage and can be used in both studying and monitoring cats with cardiac disease. Moreover, the evaluation of the thyroid profile is very important as hyperthyroid cats concomitant cardiovascular diseases are very common and they can also be a direct consequence of endocrinopathy. The purpose of this manuscript is to provide the widest possible overview of what is present in the literature about the feline clinical pathology of heart diseases through a rational division of the main alterations of traditional tests and biomarkers.

Serum symmetric dimethylarginine shows a relatively consistent long-term concentration in healthy dogs with a significant effect of increased body fat percentage

Symmetric dimethylarginine (SDMA) is a promising renal marker that correlates well with the glomerular filtration rate and could allow earlier detection of impaired renal function. The main objectives of this study were to assess the long-term variability of SDMA in healthy dogs and examine the influence of an increased body fat percentage on the level of SDMA. Sixteen lean Beagles were randomly assigned to the control group or weight-change group in age- and gender-matched pairs. The energy intake of the control group (n = 8) was strictly regulated to maintain an ideal body weight for 83 weeks, while the weight-change group (n = 8) was fed to induce weight gain (week 0–47), to maintain stable excessive body weight (week 47–56) and to lose weight (week 56–83), consecutively. At 8 specified time points, the body condition score, body composition, glomerular filtration rate, serum concentration of SDMA and creatinine were analyzed. In the control group, the within-subject coefficient of variation, between-subject coefficient of variation, reference change value (type I error = 5%) and index of individuality were 0.16, 0.22, 0.43 and 0.73, respectively. The control group and weight-change group did not differ significantly in SDMA concentration. SDMA showed a significant negative association (coefficient = -0.07) with body fat percentage (p<0.01) in the weight-change group and a significant positive association (coefficient = 7.79) with serum creatinine (p<0.01) in the entire study population. In conclusion, SDMA concentration has high long-term stability in healthy adult dogs. For the evaluation of SDMA concentrations, subject-specific reference values are preferred over a population-based reference value seen their higher sensitivity. Moreover, an increased body fat percentage does seem to affect the serum SDMA concentration of otherwise healthy dogs, but its clinical relevance has to be clarified in further research.

A Review of Specific Biomarkers of Chronic Renal Injury and Their Potential Application in Nonclinical Safety Assessment Studies

A host of novel renal biomarkers have been developed over the past few decades which have enhanced monitoring of renal disease and drug-induced kidney injury in both preclinical studies and in humans. Since chronic kidney disease (CKD) and acute kidney injury (AKI) share similar underlying mechanisms and the tubulointerstitial compartment has a functional role in the progression of CKD, urinary biomarkers of AKI may provide predictive information in chronic renal disease. Numerous studies have explored whether the recent AKI biomarkers could improve upon the standard clinical biomarkers, estimated glomerular filtration rate (eGFR), and urinary albumin to creatinine ratio, for predicting outcomes in CKD patients. This review is an introduction to alternative assays that can be utilized in chronic (>3 months duration) nonclinical safety studies to provide information on renal dysfunction and to demonstrate specific situations where these assays could be utilized in nonclinical drug development. Novel biomarkers such as symmetrical dimethyl arginine, dickkopf homolog 3, and cystatin C predict chronic renal injury in animals, act as surrogates for GFR, and may predict changes in GFR in patients over time, ultimately providing a bridge from preclinical to clinical renal monitoring.

Symmetric dimethylarginine and creatinine concentrations in serum of healthy draft horses

Background

Symmetric dimethylarginine (SDMA) is considered a more sensitive indirect estimate of glomerular filtration rate (GFR) than creatinine (Cr). Symmetric dimethylarginine is not affected by sex or muscle mass in small animals.

Objectives

To validate a commercial SDMA immunoassay (IA) for equine serum; to compare SDMA and Cr in cohorts of draft horse breeds; and to assess effects of age, sex, and breed.

Animals

One hundred and sixty‐five healthy draft horses (0.5‐16 years), including 63 Percherons, 52 Clydesdales, and 50 Belgians.

Methods

Cross‐sectional study. The SDMA IA was validated for equine serum by comparison to liquid chromatography‐mass spectroscopy (LC‐MS) results and other methods. Symmetric dimethylarginine and Cr were compared by analysis of variance and correlation analysis.

Results

Median and 95% confidence intervals (CIs) for LC‐MS (10.0 [9.4, 10.2] μg/dL) and IA (9.7 [9.5, 10.0] μg/dL) SDMA concentrations were strongly correlated (R = .74, P < .001). Symmetric dimethylarginine was lower (P < .01) in Percherons and Belgians, than in Clydesdales. Median values and 95% CI for Cr were 1.3 (1.2, 1.4), 1.4 (1.3, 1.5), and 1.4 (1.3, 1.5) mg/dL (P = .06) for Percherons, Clydesdales, and Belgians, respectively. Symmetric dimethylarginine was correlated to Cr (LC‐MS, R = .60, P < .001; IA, R = .66, P < .001). There were no differences in SDMA or Cr between sexes and there were no correlations between age and SDMA or Cr.

Conclusions and Clinical Importance

Although a significant breed effect on SDMA concentration was found, differences were small and all medians were <14 μg/dL, the cutoff value to support renal dysfunction in dogs and cats.

Plasma symmetric dimethylarginine and creatinine concentrations and glomerular filtration rate in cats with normal and decreased renal function

Background

Glomerular filtration rate (GFR) is the gold standard in assessing renal function but is impractical. Serum creatinine (sCr) has limited sensitivity in identifying early chronic kidney disease (CKD), whereas symmetric dimethylarginine (SDMA) has been commercialized as more accurate biomarker. Studies comparing SDMA and sCr with GFR in cats are limited.

Objectives

To further investigate the diagnostic performance of SDMA in nonazotemic and azotemic cats.

Animals

Forty‐nine client‐owned cats: 17 cats with CKD, 15 cats with diabetes mellitus (DM), and 17 healthy cats.

Methods

Retrospective study using spare blood samples from cats with documented sCr and GFR results for SDMA analysis. Diagnostic performances of SDMA and sCr were evaluated using correlation coefficients, sensitivities, specificities, and receiver operator characteristic curves.

Results

Compared to healthy cats and cats with DM, CKD cats had significantly higher SDMA_plasma (26.7 ± 9.9 μg/dL) and sCr (249.7 ± 71.6 μmol/L [2.8 ± 0.8 mg/dL]; both P < .001) values. SDMA_plasma (τ_B = −0.57; P < .001) and sCr (τ_B = −0.56; P < .001) were significantly correlated with GFR. SDMA_plasma (τ_B = 0.52; P < .001) had a significant relationship with sCr. SDMA_plasma and sCr had similar sensitivity (76%‐94% and 71%‐88%, respectively) in detecting reduced renal function. Creatinine had higher specificity (94%‐96%) than SDMA_plasma (75%‐76%) (P < .05).

Conclusion and Clinical Importance

In this study of azotemic and nonazotemic cats, SDMA was a reliable marker to identify decreased GFR. However, superiority of SDMA over sCr could not be confirmed.

The new age of renal biomarkers: does SDMA solve all of our problems?

Within clinical small animal practice, diagnosis of both chronic kidney disease and acute kidney injury is common. To assess renal function, measurement of glomerular filtration rate is considered the gold standard. Currently, routine tests of kidney function include surrogate markers of glomerular filtration rate such as serum creatinine, and urea, each with their own limitations, whilst urine protein to creatinine ratio gives an indication of glomerular and tubular handling of protein, and urine specific gravity information about urine concentrating ability by the kidney. These parameters are used together with historical and physical examination data to give a diagnosis of kidney disease following which creatinine, proteinuria and blood pressure are used to stage chronic kidney disease and, together with urine output, grade acute kidney injury according to the International Renal Interest Society. However, there has been much concern that creatinine is insensitive when used to indicate early decline in renal function and this has highlighted the need for additional methods of diagnosing and monitoring these patients, with the potential to allow earlier therapeutic intervention. Symmetric dimethylarginine is a novel biomarker, which has been shown to perform as a surrogate marker of glomerular filtration rate in small animals. This article will review current research on symmetric dimethylarginine and the ways in which it may be utilised in small animal practice; current research supports the use of symmetric dimethylarginine as a screening test for detection of early chronic kidney disease according to International Renal Interest Society guidelines, but further research is required in to the usefulness of symmetric dimethylarginine as a tool for monitoring disease and the effect of non-renal influences.

Retrospective evaluation of Vitis vinifera ingestion in dogs presented to emergency clinics in the UK (2012-2016): 606 Cases

OBJECTIVE

To assess key presenting signs in dogs following Vitis vinifera fruit (VVF) ingestion (grapes, raisins, currants, and sultanas), outcome, and the incidence of acute kidney injury (AKI).

DESIGN

Retrospective study (2012-2016).

SETTING

Out-of-hours clinics in the United Kingdom.

ANIMALS

The study population included 606 dogs attending 53 emergency clinics across the United Kingdom following ingestion of VVF.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Vitis vinifera fruits were found in vomit after more than 12 hours after ingestion. There was an increased incidence in December. Serum creatinine or urea was measured in 338 dogs; all were within reference intervals. In this cohort of dogs with VVF ingestion, there is no evidence for significant AKI in 32 of 33 cases within 24 hours of admission where supportive measures were introduced and repeated assessments of creatinine concentration were performed.

CONCLUSIONS

All dogs survived to discharge. One out of 33 cases with repeated creatinine concentration developed IRIS AKI grade I within 24 hours following VVF ingestion, when current emergency treatment guidelines were followed in whole or part.

Rapid Resolution of Non-Effusive Feline Infectious Peritonitis Uveitis with an Oral Adenosine Nucleoside Analogue and Feline Interferon Omega

This is the first report of a successful treatment of a non-effusive feline infectious peritonitis (FIP) uveitis case using an oral adenosine nucleoside analogue drug and feline interferon omega, and alpha-1 acid glycoprotein (AGP) as an indicator of recovery. A 2-year-old male neutered Norwegian Forest Cat presented with uveitis, keratic precipitates, mesenteric lymphadenopathy and weight loss. The cat was hypergammaglobulinaemic and had a non-regenerative anaemia. Feline coronavirus (FCoV) RNA was detected in a mesenteric lymph node fine-needle aspirate by a reverse-transcriptase polymerase chain reaction—non-effusive FIP was diagnosed. Prednisolone acetate eye drops were administered three times daily for 2 weeks. Oral adenosine nucleoside analogue (Mutian) treatment started. Within 50 days of Mutian treatment, the cat had gained over one kilogram in weight, his globulin level reduced from 77 to 51 g/L and his haematocrit increased from 22 to 35%; his uveitis resolved and his sight improved. Serum AGP level reduced from 3100 to 400 μg/mL (within normal limits). Symmetric dimethylarginine (SDMA) was above normal at 28 μg/dL, reducing to 14 μg/dL on the cessation of treatment; whether the SDMA increase was due to FIP lesions in the kidney or Mutian is unknown. Mutian treatment stopped and low-dose oral recombinant feline interferon omega begun—the cat’s recovery continued.

Effect of Added Dietary Betaine and Soluble Fiber on Metabolites and Fecal Microbiome in Dogs with Early Renal Disease

Renal diets are recommended for dogs with chronic kidney disease (CKD). This study examined the effects of foods with added betaine and fiber on the plasma and fecal metabolome and fecal microbiome in dogs with early stage CKD. At baseline, several metabolites differed between healthy dogs and those with CKD. Dogs with CKD (n = 28) received a control food, low soluble fiber plus betaine food (0.5% betaine, 0.39% oat beta-glucan, and 0.27% short-chain fructooligosaccharides (scFOS)), or high soluble fiber plus betaine food (0.5% betaine, 0.59% oat beta-glucan, and 0.41% scFOS) each for 10 weeks in different sequences. Consumption of test foods led to several favorable, significant changes in the plasma metabolome, including decreases of several uremic toxins and other deleterious metabolites, and increases in favorable metabolites compared with the control food. Only 7 fecal metabolites significantly changed with consumption of the test foods compared with the control food, largely increases in polyphenols and lignans. Few changes were seen in the fecal microbiome, though some taxa that significantly changed in response to the test foods have beneficial effects on health, with some negatively correlating with uremic toxins. Overall, foods with added betaine and soluble fiber showed positive effects on the plasma and fecal metabolomes.

Symmetric dimethylarginine concentrations in dogs with hypothyroidism before and after treatement with levothyroxine

OBJECTIVES

To evaluate the serum symmetric dimethylarginine (SDMA) and serum creatinine concentrations in a population of hypothyroid dogs at the time of diagnosis and after treatment.

MATERIALS AND METHODS

Serum SDMA and serum creatinine were measured in serum samples of 24 healthy dogs and 24 hypothyroid dogs, at the time of diagnosis (T0) and after supplementation with levothyroxine (T1).

RESULTS

The mean SDMA concentrations (reference intervals [RI] <18 μg/dL and <14 μg/dL depending on the source) were 11.7 ± 3.5 μg/dL, 13.8 ± 3.1 μg/dL and 11.83 ± 2.87 μg/dL in healthy dogs, and in the hypothyroid dogs at T0 and T1, respectively. The SDMA concentrations were higher in the hypothyroid dogs at T0 in comparison with the healthy dogs. Of the hypothyroid dogs, 1 out of 24 had an SDMA concentration above 18 μg/dL and 12 out of 24 above 14 μg/dL at T0. At T1, none of the hypothyroid dogs had SDMA concentrations above 18 μg/dL and two of them had SDMA concentrations above 14 μg/dL. The serum creatinine concentration was higher in the hypothyroid dogs at T0 as compared to the healthy dogs. At T0, 8 out of 24 hypothyroid dogs had serum creatinine concentrations above the RI (>1.4 mg/dL). In all but one dog, serum creatinine normalised after treatment.

CLINICAL SIGNIFICANCE

The SDMA and serum creatinine concentrations were higher in hypothyroid dogs at diagnosis as compared to healthy dogs. Serum creatinine concentrations were increased in one-third of the hypothyroid dogs and in the majority of cases normalised after levothyroxine supplementation. SDMA concentrations were rarely above the upper limit of the RI when the higest (<18 μg/dL) cut-off was employed. The diagnostic accuracy of SDMA in dogs with thyroid dysfunction requires additional evaluation.

Biologic variation of symmetric dimethylarginine and creatinine in clinically healthy cats

BACKGROUND

Biologic variation of biochemical analytes, both within individuals and between individuals, determines whether population-based reference intervals (RIs) are appropriate when interpreting if a particular change is clinically relevant for a specific individual.

OBJECTIVES

We aimed to evaluate the biologic variation of symmetric dimethylarginine (SDMA) in clinically healthy cats.

METHODS

A prospective, observational study was performed in which 10 clinically healthy, client-owned cats were sampled for serum biochemical analyses once weekly for 6 weeks. Serum samples were frozen, and then single batches were analyzed for SDMA, using both liquid chromatography-mass spectroscopy (LC-MS), and an enzyme multiplied immunoassay technique (EMIT), and creatinine by modified Jaffe method. Restricted maximum likelihood estimations were used to determine the coefficients of variation (CVs) describing variation within each cat, between cats, and the analytical variation. These CVs were used to determine the indices of individuality and reference change values (RCVs).

RESULTS

SDMA had an intermediate index of individuality that could be evaluated by both RCV and population-based RIs. In contrast, creatinine had a high index of individuality best evaluated with RCVs. Serum SDMA concentrations evaluated with either the reference standard, LC-MS, or the clinically used EMIT yielded similar results.

CONCLUSIONS

Clinicians should consider biologic variation when selecting the best method for interpreting changes in biochemical analytes. Specifically, establishing each cat's baseline serum creatinine and SDMA concentrations during health, and applying RCVs to subsequent measurements could improve the recognition of meaningful biologic changes.

First report of Cytauxzoon sp. infection in Germany: organism description and molecular confirmation in a domestic cat

Cytauxzoonosis is described as an emerging tick-borne disease of domestic and wild felids caused by protozoans of the genus Cytauxzoon. While in the Americas the condition is described as a fatal disease, in Europe, reports on the clinical expression of the infection are scarce. This study describes the first case of Cytauxzoon sp. infection in Germany, in a domestic cat. A 6-year-old male domestic cat living in Saarlouis (Saarland) was presented with anorexia, lethargy and weight loss. The cat had an outdoor lifestyle and had not travelled abroad. Serum clinical chemistry analysis revealed azotaemia with markedly increased symmetric dimethylarginine, hypercreatinemia, hyperphosphatemia and hypoalbuminemia. Moreover, a mild non-regenerative anaemia was present. Approximately 1 year prior to these findings, the domestic cat was diagnosed with a feline immunodeficiency virus (FIV) infection. These results pointed toward a decreased glomerular filtration rate, presumably as a result of kidney dysfunction. Round to oval signet ring–shaped intraerythrocytic organisms, morphologically suggestive for a piroplasm, were revealed during blood smear evaluation with a degree of parasitaemia of 33.0%. PCR analyses and sequencing of a region of the 18S rRNA gene confirmed the presence of a Cytauxzoon sp. infection, with 99–100% nucleotide sequence identity with previously published Cytauxzoon sp. isolates. As this is the first molecularly confirmed Cytauxzoon sp. infection in a domestic cat in Germany, these findings suggest that cytauxzoonosis should be considered as a differential diagnosis in cases of anaemia in outdoor domestic cats, particularly in areas where wild felid populations are present.

Canine Traditional Laboratory Tests and Cardiac Biomarkers

In small animals, cardiac disease evaluation through laboratory tests can be a challenge. This review will present both historical and updated perspectives on the clinical pathology of cardiac diseases in dogs and demonstrate that laboratory tests are useful tools for the management of patients with cardiac diseases.