Factors affecting urine specific gravity in apparently healthy cats presenting to first opinion practice for routine evaluation

Optimization and validation of metabolomics methods for feline urine and serum towards application in veterinary medicine

BACKGROUND

Metabolomics is an emerging and powerful technology that offers a comprehensive view of an organism's physiological status. Although widely applied in human medicine, it is only recently making its introduction in veterinary medicine. As a result, validated metabolomics protocols in feline medicine are lacking at the moment. Since biological interpretation of metabolomics data can be misled by the extraction method used, species and matrix-specific optimized and validated metabolomic protocols are sorely needed.

RESULTS

Systematic optimization was performed using fractional factorial experiments for both serum (n = 57) and urine (n = 24), evaluating dilution for both matrices, and aliquot and solvent volume, protein precipitation time and temperature for serum. For the targeted (n = 76) and untargeted (n = 1949) validation of serum respectively, excellent instrumental, intra-assay and inter-day precision were observed (CV ≤ 15% or 30%, respectively). Linearity deemed sufficient both targeted and untargeted (R2 ≥ 0.99 or 0.90, respectively). An appropriate targeted recovery between 70 and 130% was achieved. For the targeted (n = 69) and untargeted (n = 2348) validation of the urinary protocol, excellent instrumental and intra-assay precision were obtained (CV ≤ 15% or 30%, respectively). Subsequently, the discriminative ability of our metabolomics methods was confirmed for feline chronic kidney disease (CKD) by univariate statistics (n = 41 significant metabolites for serum, and n = 55 for urine, p-value<0.05) and validated OPLS-DA models (R2(Y) > 0.95, Q2(Y) > 0.65, p-value<0.001 for both matrices).

SIGNIFICANCE

This study is the first to present an optimized and validated wholistic metabolomics methods for feline serum and urine using ultra-high performance liquid chromatography coupled to quadrupole-Orbitrap high-resolution mass spectrometry. This robust methodology opens avenues for biomarker panel selection and a deeper understanding of feline CKD pathophysiology and other feline applications.

Exploring the relationship between calcitonin, ionized calcium, and bone turnover in cats with and without naturally occurring hypercalcemia

Objectives

This case-control study aimed to evaluate calcitonin response in naturally occurring hypercalcemia in cats and assess the relationships between calcitonin and ionized calcium (iCa) and examine relationships between calcitonin, iCa and bone turnover.

Methods

Hypercalcemic cats (persistently increased iCa concentration [>1.40 mmol/l]) were identified retrospectively via a medical database search; additional hypercalcemic and normocalcemic cats were recruited prospectively. Data regarding routine biochemical and urine testing, diagnostic imaging and additional blood testing were obtained. Serum alkaline phosphatase (ALP) activity was used as a marker of bone turnover. Serum calcitonin concentration was analyzed using a previously validated immunoradiometric assay. Hypercalcemic cats with an increased calcitonin concentration (>0.9 ng/L) were termed responders. Group comparisons were performed using a Mann-Whitney test for continuous variables and a χ2 test for categorical variables. Spearman's correlation coefficient was used to examine the relationships between calcitonin, iCa and ALP.

Results

Twenty-six hypercalcemic and 25 normocalcemic cats were recruited. Only 5/26 (19.2%) of the hypercalcemic cats were identified as responders, and all were diagnosed with idiopathic hypercalcemia. There was no significant correlation between the concentrations of calcitonin and iCa (p = 0.929), calcitonin and ALP (p = 0.917) or iCa and ALP (p = 0.678) in hypercalcemic cats, however, a significant negative correlation was observed between calcitonin and ALP (p = 0.037) when normocalcemic and hypercalcemic cats with an elevated calcitonin concentration were analyzed together.

Discussion

The expected increase in calcitonin concentration was present in only a small subset of hypercalcemic cats; no correlation was found between iCa and calcitonin concentration. The inverse relationship between calcitonin and ALP in cats with increased calcitonin concentrations suggests that the ability of calcitonin to correct hypercalcemia may be related to the degree of bone turnover.

Determination of the reference interval for urine kidney injury molecule-1 in 50 healthy cats

OBJECTIVES

The aim of the present study was to establish a reference interval (RI) for urine kidney injury molecule-1 (KIM-1) in healthy cats.

METHODS

History, physical examination, blood pressure, and feline immunodeficiency virus and feline leukemia virus serology status were determined. A complete blood cell count, serum biochemical profile, urinalysis and kidney ultrasound were performed, and N-terminal pro-brain natriuretic peptide, total thyroxine (TT4) and urine KIM-1 were measured. An RI was calculated and the effect of age, sex, body condition score (BCS), blood pressure, symmetric dimethylarginine (SDMA), serum creatinine concentration (SCr), phosphorus, TT4, urine specific gravity (USG) and mid-sagittal kidney length on urine KIM-1 was evaluated using a general linear model.

RESULTS

Of 69 recruited cats, 50 met the inclusion criteria. There were 35 male cats and 15 female cats, with a median age of 4.3 years (range 1.0-12.3), median weight of 5.11 kg (range 2.52-8.45) and median BCS of 6/9 (range 3-8). The median serum concentrations were SDMA 11.0 µg/dl (range 2-14), SCr 88.5 µmol/l (range 47-136), phosphorus 1.41 mmol/l (range 0.8-2.2) and TT4 32.0 nmol/l (range 17-51). Median USG was 1.057 (range 1.035-1.076), mid-sagittal left kidney length was 3.50 cm (range 2.94-4.45) and mid-sagittal right kidney length was 3.70 cm (range 3.06-4.55). The derived RI for urine KIM-1 was 0.02-0.68. USG was a significant (P <0.001) predictor of urine KIM-1. Individually, age, sex, blood pressure, BCS, SDMA, SCr, phosphorus, TT4 and mid-sagittal kidney length were not significant predictors of urine KIM-1. In a multivariate model, if combined with USG, SDMA concentration was predictive (P = 0.030) of urine KIM-1.

CONCLUSIONS AND RELEVANCE

Urine concentration was significantly correlated with urine KIM-1, which will be an important consideration when interpreting findings in cats with potential kidney injury.

Urine concentrating ability in cats with hyperthyroidism: Influence of radioiodine treatment, masked azotemia, and iatrogenic hypothyroidism

BACKGROUND

Hyperthyroid cats often have urine specific gravity (USG) values <1.035. It remains unclear how USG changes after treatment, if USG can be used to predict azotemia after treatment, or how iatrogenic hypothyroidism influences USG values.

OBJECTIVES

To determine the proportion of hyperthyroid cats with USG <1.035 vs ≥1.035; if USG changes after treatment; and whether USG <1.035 correlated with unmasking of azotemia or hypothyroidism.

ANIMALS

Six hundred fifty-five hyperthyroid cats treated with radioiodine; 190 clinically normal cats.

METHODS

Prospective, before-and-after study. Hyperthyroid cats had serum thyroxine, thyroid-stimulating hormone, and creatinine concentrations, and USG measured before and 6 months after successful treatment with radioiodine.

RESULTS

Of untreated hyperthyroid cats, USG was ≥1.035 in 346 (52.8%) and <1.035 in 309 (47.2%). After treatment, 279/346 (80.6%) maintained USG ≥1.035, whereas 67/346 (19.4%) became <1.035; 272/309 (88%) maintained USG <1.035, whereas 37/309 (12%) became ≥1.035. Only 22/346 (6.4%) with USG ≥1.035 developed azotemia after treatment, compared with 136/309 (44%) with <1.035 (P < .001). Of cats remaining nonazotemic, 38% had USG <1.035, compared with 20% of normal cats (P < .001). The 137 cats with iatrogenic hypothyroidism had lower USG after treatment than did 508 euthyroid cats (1.024 vs 1.035), but USGs did not change after levothyroxine supplementation. USG <1.035 had high sensitivity (86.1%) but moderate specificity (65.2%) in predicting azotemia after treatment.

CONCLUSIONS AND CLINICAL IMPORTANCE

Hyperthyroidism appears not to affect USG in cats. However, cats with evidence of sub-optimal concentrating ability before radioiodine treatment (USG < 1.035) are more likely to develop azotemia and unmask previously occult chronic kidney disease. Iatrogenic hypothyroidism itself did not appear to affect USG values.

Biological variation of urinary protein: Creatinine ratio and urine specific gravity in cats

BACKGROUND

Laboratory results are influenced by presence and severity of disease, as well as preanalytical factors, analytical variation, and biological variation. Biological variation data for urinary protein: creatinine ratio (UPC) and urine specific gravity (USG) in cats are lacking.

OBJECTIVES

Determine the biological variation of UPC and USG in cats.

ANIMALS

Eighty healthy client-owned cats.

METHODS

Prospective study. Urine was collected on days 0, 14, and 56 from all 80 cats to investigate the persistence of borderline or overt proteinuria or suboptimal urine concentration. In 15 of these cats, urine was collected weekly from day 0 to 42 to calculate the index of individuality (II) and reference change value (RCV), and on days 56 and 57 to evaluate day-to-day variability of UPC and USG.

RESULTS

Borderline or overt proteinuria (UPC ≥0.2) was present in 18/80 (23%) cats at baseline and persisted on 3 occasions in 2 months in 8/18 (44%) cats. Urine concentration was suboptimal at inclusion (USG <1.035) in 8/80 (10%) cats and at all 3 time points during 2 months in 3/8 (38%) cats. The II of UPC and USG indicated intermediate individuality. The 1-sided RCV was 82% for UPC and 36% for USG. Proteinuria substage was identical on 2 consecutive days in 13/15 (87%) cats, and urine concentrating ability remained the same in all 15 cats.

CONCLUSIONS AND CLINICAL IMPORTANCE

A >82% increase in UPC in a healthy cat is not solely attributable to physiological and analytical variation. For USG, a decrease of >36% is considered clinically relevant.

Longitudinal examination of urine pH, specific gravity, protein, culture, and antimicrobial resistance profiles in healthy dogs

BACKGROUND

Urine is routinely evaluated in dogs to assess health. Reference ranges for many urine properties are well established, but the scope of variation in these properties over time within healthy dogs is not well characterized.

OBJECTIVES

Longitudinally characterize urine properties in healthy dogs over 3 months.

ANIMALS

Fourteen healthy client-owned dogs.

METHODS

In this prospective study, dogs were evaluated for health; then, mid-stream free-catch urine was collected from each dog at 12 timepoints over 3 months. Urine pH, urine specific gravity (USG), protein, cultures, and antimicrobial resistance profiles were assessed at each timepoint.

RESULTS

Urine pH varied within and between dogs over time (Friedman's test: within P = .03; between P < .005). However, USG, protein, and bacterial diversity of urine were consistent within dogs over time, and only varied between dogs (Kruskal-Wallis: between all P < .005). Antimicrobial resistant isolates were identified in 12 out of 14 dogs with 34 of 48 of the isolates demonstrating resistance to amoxicillin.

CONCLUSIONS AND CLINICAL IMPORTANCE

Urine pH should be assessed at multiple timepoints via pH meter before making clinical decisions. Mid-stream free-catch urine with high concentrations of bacteria (>105  CFU/mL) should not be considered the only indicator of urinary tract infection. Bacterial isolates from dogs in this study had widespread resistance to amoxicillin/oxacillin underscoring the need for antimicrobial stewardship.

[Urinalysis in dogs and cats, part 1: physical and chemical urinalysis]

The urinalysis of dogs and cats is an important part of the diagnostic evaluation of urinary tract diseases as well as for the identification of systemic diseases. A routine urinalysis consists of a physical and chemical examination of the urine as well as an examination of the urine sediment. Various urine collection methods (free-catch, catheterization, cystocentesis) are available. Each method has multiple advantages and disadvantages. The appropriate method must be chosen individually for each patient depending on the emphasis of the examination. The urine should ideally be examined within 30 minutes of collection as it is prone to change due to time and storage. Physical examination of the urine consists of the determination of urine color, clarity, and specific gravity which provides information regarding the concentration of the urine. The latter is determined by refractometry and needs to be interpreted in the context of the hydration status of the patient. Chemical examination of the urine consists of the determination of the pH value and the presence of blood/hemoglobin/myoglobin, protein, glucose, bilirubin, urobilinogen, nitrite, and ketones. The use of commercially available urine dipsticks is common. These must be stored and used according to the manufacturer's instructions and when interpreting the results, veterinary aspects need to be taken into consideration. The physical and chemical examinations of the urine represent rapid and readily performable methods that provide important information for the diagnosis or the exclusion of numerous diseases.

Frequency of histologic lesions in the kidneys of cats without kidney disease

OBJECTIVES

In humans, renal aging is associated with an increased frequency of glomerulosclerosis, interstitial fibrosis, inflammation and tubular atrophy. The purpose of this study was to describe the frequency of renal histopathologic lesions in cats without kidney disease.

METHODS

A cross-sectional study of archival kidney tissue from 74 cats without kidney disease (serum creatinine <1.6 mg/dl; urine specific gravity >1.035) was carried out: 0-4 years (young, n = 18); 5-9 years (mature, n = 16); 10-14 years (senior, n = 34), 15+ years (geriatric, n = 6). Glomerulosclerosis, tubular atrophy, interstitial inflammation and fibrosis, and the presence or absence of lipid in the interstitium and tubules were scored by a pathologist masked to clinical data. Statistical analyses were performed as appropriate.

RESULTS

Geriatric cats had significantly more glomerulosclerosis than mature (P = 0.01) and young cats (P = 0.004). Senior cats had significantly more glomerulosclerosis than young cats (P = 0.006). Glomerulosclerosis was weakly positively correlated with age (r = 0.48; P <0.0001). Geriatric cats had significantly more tubular atrophy than mature (P = 0.02) and young cats (P <0.0001). Senior cats had significantly more tubular atrophy than young cats (P <0.0001). Geriatric cats had significantly more inflammation than senior cats (P = 0.02), mature cats (P = 0.01) and young cats (P <0.0001). Senior cats had significantly more inflammation than young cats (P = 0.004). Geriatric and senior cats had significantly more fibrosis than young cats (P = 0.01 and P = 0.04, respectively). Frequency of tubular lipid increased with age (young: 28%; mature: 56%; senior: 79%; geriatric: 100%) as did the frequency of interstitial lipid (young: 22%, mature: 56%, senior: 85%, geriatric: 100%).

CONCLUSIONS AND RELEVANCE

Evidence of renal aging exists in cats. These changes imply that the aging kidney may be more susceptible to injury and impaired healing.

Case Report: Imaging Features and Successful Management of Ureteral Stenosis in a Kitten With Bilateral Atypical Papillary Transitional Mucosal Hyperplasia

A 3-month-old cat weighing 2.62 kg was brought to the VIP Animal Medical Center with vomiting, diarrhea, anorexia, and depression. Laboratory findings confirmed azotemia with elevated blood urea nitrogen (BUN) (168.9 mg/dl) and creatinine (5.9 mg/dl) and symmetric dimethylarginine (SDMA) (86 μg/dl). Abdominal radiography revealed bilateral renomegaly. Ultrasonography revealed bilateral hydronephrosis and left partial and right complete ureteral obstructions with bilateral focal irregular and circumferential thickenings at ureters. Reduction of bilateral renal function was confirmed through excretory urography on computed tomography. The cat underwent subcutaneous ureteral bypass surgery on the left kidney, right nephrectomy, and bilateral ureterectomy. Histopathology of bilateral ureteral irregular and circumferential thickening revealed bilateral atypical papillary transitional mucosal hyperplasia. Three days after surgery, the left hydronephrosis resolved, and azotemia was almost resolved. This is the first report of successful management of ureteral stenosis with congenital papillary transitional mucosal hyperplasia in a kitten using multimodality imaging.

Urinalysis in dog and cat: A review

Urinalysis is the examination of normal and abnormal constituents of urine. It is an easy, cheap, and vital initial diagnostic test for veterinarians. Complete urinalysis includes the examination of color, odor, turbidity, volume, pH, specific gravity, protein, glucose, ketones, blood, erythrocytes, leukocytes, epithelial cells, casts, crystal, and organisms. Semi-quantitative urine analysis with urine dipsticks, as well as an automatic analyzer, provides multiple biochemical data. Contamination is almost entirely avoided if the protocols for ensuring a proper sample have been followed, as mentioned still consideration must be given to the likelihood of contamination, even if the sample is correctly obtained. Interpretation of urinalysis will be doubtful if the knowledge of the interference is limited. Well-standardized urinalysis, when correlated in the context of history, clinical findings, and other diagnostic test results, can identify both renal and non-renal disease. This paper reviews significance of different components of urinalysis of dog and cat, such as collection, storage, examination, interpretation, and common causes of error in the result.

Clinical outcomes of 28 cats 12-24 months after urethrostomy

OBJECTIVES

The aim of this study was to evaluate and compare the long-term clinical outcomes and quality of life of cats having undergone perineal urethrostomy (PU) or prepubic urethrostomy (PPU).

METHODS

This clinical study followed 28 cats (PU, n = 22; PPU, n = 6) that underwent a urethrostomy, with a minimum of 1 year postoperative follow-up. Medical records, pet owner surveys and urologic laboratory tests were used for assessment. Urologic laboratory tests included serum symmetric dimethylarginine (SDMA), serum creatinine, urinalysis, urine specific gravity (USG), urine protein:creatinine (UPC) ratio and urine culture.

RESULTS

The main indications for urethrostomy were multiple catheterizations and PU stricture. The overall complication rates of PU and PPU were 31.8% and 83.3%, respectively. Recurrent urinary tract infection (UTI) and urine scald dermatitis were less frequent in PU than in PPU cats (UTI 22.7% vs 66.6%; dermatitis 4.5% vs 83.3%). Bacteriuria was present in 77.2% and 100% of PU and PPU cats, respectively. Owner satisfaction rates were excellent in 81.8% of PU and 33.3% of PPU cases.

CONCLUSIONS AND RELEVANCE

A proportion of cats that underwent urethrostomy showed bacteriuria, recurrent UTIs and increased levels of SDMA. PPU is important as a salvage procedure; however, it should be limited to cases in which standard techniques for PU cannot be performed, owing to the potential for recurrent complications and lower owner satisfaction.

Urinary specific gravity as an alternative for the normalisation of endocrine metabolite concentrations in giant panda (Ailuropoda melanoleuca) reproductive monitoring

Reproductive monitoring for captive breeding in giant pandas is based on behavioural observation and non-invasive hormone analysis. In urine, interpretation of results requires normalisation due to an animal’s changing hydration. Correction of urinary concentrations based on creatinine is the gold standard. In this study, a largely unexplored, easy-to-perform normalisation technique, based on urinary specific gravity (USpG), was examined and compared to creatinine. To this extent, six cycles from two female pandas (SB741(1) and SB569(5)) were monitored through urine analysis for oestrogen, progesterone, ceruloplasmin and 13,14-dihydro-15-keto-PGF2a (PGFM). The Pearson’s correlation between creatinine and USpG was high (r = 0.805–0.894; p < 0.01), indicative for a similar performance of both normalisation methods. However, generally lower values were observed during pro-oestrus and primary (progesterone) rise. This could be associated with huge shifts in appetite, monitored by faecal output (kg) with an averaged > 50% decrease during oestrus and >50% increase during primary progesterone rise. In parallel, respectively highest and lowest creatinine and USpG levels, were measured, with creatinine obviously more affected as a result of linkage with muscle tissue metabolism affected by reproductive hormones. As a consequence, metabolite levels were significantly different between both corrected datasets with significantly higher oestrogen peak levels during oestrus ranging from 2.13–86.93 and 31.61–306.45 ng/mL (USpG correction) versus 2.33–31.20 and 36.36–249.05 ng/mL Cr (creatinine correction) for SB569 and SB741 respectively, and significant lower progesterone levels during primary progesterone rise ranging from 0.35–3.21 and 0.85–6.80 ng/mL (USpG correction) versus 0.52–10.31 and 2.10–272.74 ng/mL Cr (creatinine correction) for SB569 and SB741 respectively. Consequently, USpG correction rendered unbiased profiles, less subject to variation and metabolic artefacts and therefore allowed a more straightforward identification of peak oestrogen and onset of secondary progesterone rise, being potentially advantageous for future studies unravelling key giant panda reproductive events, including (delayed) implantation. The alternative application of USpG as a normalisation factor was further supported by its easy application and environmental and technical robustness.

ISFM Consensus Guidelines on the Diagnosis and Management of Feline Chronic Kidney Disease

PRACTICAL RELEVANCE

Chronic kidney disease (CKD) is one of the most commonly diagnosed diseases in older cats. In most cats, CKD is also a progressive disease and can be accompanied by a wide range of clinical and clinicopathological changes. These ISFM Consensus Guidelines have been developed by an independent panel of clinicians and academics to provide practical advice on the diagnosis and management of this complex disease.

CLINICAL CHALLENGES

Although CKD is a common clinical problem in cats, the manifestations of disease vary between individuals. Thus there is a need for careful and repeat evaluation of cats with CKD and adjustment of therapy according to individual needs. In addition to addressing problems arising from CKD and improving quality of life (QoL) for the patient, therapy may also target slowing the underlying progression of disease and hence prolonging life. While maintaining QoL is of paramount importance in our patients, this can be challenging when multiple therapies are indicated. In some cases it is necessary to prioritise therapy, given an understanding of what is likely to most benefit the individual patient.

EVIDENCE BASE

In preparing these Guidelines, the Panel has carefully reviewed the existing published literature, and has also graded the quality of evidence for different interventions to help to provide practical recommendations on the therapeutic options for feline CKD. This is a field of veterinary medicine that has benefited from some excellent published clinical research and further research findings will undoubtedly modify the recommendations contained in these Guidelines in the future.

Practical urinalysis in the cat: 1: Urine macroscopic examination 'tips and traps'

SERIES OUTLINE

This is the first article in a two-part series on urinalysis in the cat. The focus of Part 1 is urine macroscopic examination. Part 2, to appear in the May 2016 issue, discusses urine microscopic examination.

PRACTICAL RELEVANCE

Urinalysis is an essential procedure in feline medicine but often little attention is paid to optimising the data yielded or minimising factors that can affect the results.

CLINICAL CHALLENGES

For the best results, appropriately collected urine should be prepared promptly by specialist laboratory personnel for the relevant tests and assessed by a clinical pathologist. This is invariably impractical in clinical settings but careful attention can minimise artefacts and allow maximum useful information to be obtained from this seemingly simple process.

AUDIENCE

Clinical pathologists would be familiar with the information provided in this article, but it is rarely available to general or specialist practitioners, and both can potentially benefit.

EQUIPMENT

Most of the required equipment is routinely available to veterinarians. However, instructions have been provided to give practical alternatives for specialist procedures in some instances.

EVIDENCE BASE

Evidence for much of the data on urinalysis in cats is lacking. Validation of the human equipment used routinely, such as dipsticks, is also lacking. As such, the evidence base for feline urinalysis is quite poor and information has largely been extrapolated from the human literature. Information from feline studies has been included where available. In addition, practical clinicopathological and clinical observations are provided.

Osteitis fibrosa cystica in a domestic young cat

CASE SUMMARY

A 4-month-old cat had bilateral swellings of the mandible, maxilla, humerus and femur, and angular deviations in the axial and appendicular skeleton. The biochemical profile indicated hypercalcemia, hyperphosphatemia and increased parathyroid hormone levels. Because of the poor prognosis, the cat was euthanized. At necropsy, malleable and fragile bones, associated with numerous cystic areas containing yellowish and translucent liquid, were observed. Histologically, the bones showed marked diffuse proliferation of fibrous connective tissue, and large numbers of osteoclasts surrounding numerous cystic structures were also observed within fibrotic areas at the periphery of the trabecular bone. In addition, enlargement of the parathyroid glands, which was associated with increased serum concentrations of calcium, phosphorus and parathyroid hormone, was detected.

RELEVANCE AND NOVEL INFORMATION

The changes observed in this cat are consistent with hyperparathyroidism-associated osteitis fibrosa cystica, which is an unusual presentation in the cat. Hyperparathyroidism, either primary (neoplastic) or secondary (nutritional or renal), is the primary cause of this condition.