Prediction of acute renal failure after birth asphyxia

The Clinical Significance of Urinary Retinol-Binding Protein 4: A Review

Effective biomarkers for early diagnosis, prognostication, and monitoring in renal diseases (in general) comprise an unmet need. Urinary retinol-binding protein 4, which is the most sensitive indicator of renal tubular damage, holds great promise as a universal biomarker for renal pathologies, in which tubular injury is the driving force. Here, we summarize the most important existing data on the associations between urinary retinol-binding protein 4 and renal diseases and highlight the untapped potential of retinol-binding protein 4 in clinical use.

Tubular and Glomerular Biomarkers of Acute Kidney Injury in Newborns

BACKGROUND

Acute Kidney Injury (AKI) is a sudden decrease in kidney function. In the early period, the highest percentage of AKI occurs among newborns hospitalized in the neonatal intensive care units, especially premature neonates. The prognosis of AKI depends on the type and severity of the cause of an injury, the accuracy and the time of diagnosis and treatment. The concentration of serum creatinine is still the main diagnostic test, although it changes in the course of AKI later than glomerular filtration rate GFR. In addition, the reliability of the determination of creatinine level is limited because it depends on many factors. New studies have presented other, more useful laboratory markers of renal function that can be measured in serum and/or in urine.

OBJECTIVE

The aim of the work was to present the latest data about tubular and glomerular biomarkers of acute kidney injury in newborns.

METHODS

We undertook a structured search of bibliographic databases for peer-reviewed research literature by using focused review topics. According to the conceptual framework, the main idea of research literature has been summarized and presented in this study.

RESULTS

The concentrations of some novel biomarkers are higher in serum and/or urine of term and preterm newborns with AKI, especially in the course of perinatal asphyxia.

CONCLUSION

In this systematic review of the literature, we have highlighted the usefulness of biomarkers in predicting tubular and/or glomerular injury in newborns. However, novel biomarkers need to prove their clinical applicability, accuracy, and cost-effectiveness prior to their implementation in clinical practice.

Evaluation of various biomarkers for kidney monitoring during canine leishmaniosis treatment

Background

The objective of this study was to evaluate and compare the evolution of the profile currently recommended by the International Renal Interest Society (IRIS) (sCr, UPC and sSDMA) with a panel of other different kidney biomarkers during treatment for canine leishmaniosis. This panel included three urinary glomerular biomarkers (uIgG, uCRP and uferritin) and three urinary tubular biomarkers (uGGT, uNAG and uRBP).

These biomarkers were measured in two groups of dogs with canine leishmaniosis at IRIS stage I. Group 1: dogs showing proteinuria (UPC > 0.5) before treatment which did not decrease after treatment; Group 2: dogs showing proteinuria before treatment which decreased after treatment.

Results

Group 1 showed no significant changes in any biomarker after treatment. In group 2, among the biomarkers recommended by the IRIS, only UPC showed a significant decrease after treatment. However all biomarkers of glomerular damage showed a significant decrease after treatment, with uIgG/Cr and uCRP/Cr showing the greater decreases. In addition uRBP/Cr and uNAG/Cr showed significant decreases after treatment.

Conclusions

In dogs with leishmaniosis at IRIS stage I that reduced UPC after treatment, there were no significant changes in serum creatinine and sSDMA. However, all the urine biomarkers evaluated with exception of uGGT showed a significant decrease. These decreases were more evident in those markers related with glomerular function, being uIgG/Cr the biomarker more associated with UPC. Further studies involving a larger number of animals and histological analysis of the kidney would be recommended to confirm these findings and evaluate the routine practical use of these urine biomarkers in canine leishmaniosis.

The prevalence of acute kidney injury in neonates with birth asphyxia is higher in the Democratic Republic of Congo than in Western countries

AIM

There is very little data on acute kidney injury in neonates in Africa. The aim of this study was to describe the frequency of acute kidney injury and the outcome in neonates admitted to hospital for asphyxia in the Democratic Republic of Congo.

METHODS

A descriptive study was conducted in the country's capital Kinshasa. Acute kidney injury was diagnosed within three days of life when the creatinine clearance was ≤16 mL/min/1.73 m².

RESULTS

Acute kidney injury occurred in 54.3% of the 35 neonates with severe perinatal asphyxia and 31.4% of the 35 neonates with moderate perinatal asphyxia, and this rate was higher than the prevalence reported in Western countries. Prerenal acute kidney injury occurred in 12 (40%) of the 30 neonates with acute kidney injury. The frequency of oliguria was significantly higher in neonates with severe perinatal asphyxia than moderate perinatal asphyxia (73.7% vs. 45.5%), and mortality was also higher in neonates with severe rather than moderate perinatal asphyxia (57.9% vs. 36.4%).

CONCLUSION

The prevalence of acute kidney injury was higher in asphyxiated patients in the Democratic Republic of Congo than in Western countries. It was also higher in neonates with severe rather than moderate perinatal asphyxia.

In search of mechanisms associated with mesenchymal stem cell-based therapies for acute kidney injury

Acute kidney injury (AKI) is classically described as a rapid loss of kidney function. AKI affects more than 15% of all hospital admissions and is associated with elevated mortality rates. Although many advances have occurred, intermittent or continuous renal replacement therapies are still considered the best options for reversing mild and severe AKI syndrome. For this reason, it is essential that innovative and effective therapies, without side effects and complications, be developed to treat AKI and the end-stages of renal disease. Mesenchymal stem cell (MSC) based therapies have numerous advantages in helping to repair inflamed and damaged tissues and are being considered as a new alternative for treating kidney injuries. Numerous experimental models have shown that MSCs can act via differentiation-independent mechanisms to help renal recovery. Essentially, MSCs can secrete a pool of cytokines, growth factors and chemokines, express enzymes, interact via cell-to-cell contacts and release bioagents such as microvesicles to orchestrate renal protection. In this review, we propose seven distinct properties of MSCs which explain how renoprotection may be conferred: 1) anti-inflammatory; 2) pro-angiogenic; 3) stimulation of endogenous progenitor cells; 4) anti-apoptotic; 5) anti-fibrotic; 6) anti-oxidant; and 7) promotion of cellular reprogramming. In this context, these mechanisms, either individually or synergically, could induce renal protection and functional recovery. This review summarises the most important effects and benefits associated with MSC-based therapies in experimental renal disease models and attempts to clarify the mechanisms behind the MSC-related renoprotection. MSCs may prove to be an effective, innovative and affordable treatment for moderate and severe AKI. However, more studies need to be performed to provide a more comprehensive global understanding of MSC-related therapies and to ensure their safety for future clinical applications.

Biomarkers in the assessment of acute and chronic kidney diseases in the dog and cat

In both human and veterinary medicine, diagnosing and staging renal disease can be difficult. Measurement of glomerular filtration rate is considered the gold standard for assessing renal function but methods for its assessment can be technically challenging and impractical. The main parameters used to diagnose acute and chronic kidney disease include circulating creatinine and urea concentrations, and urine-specific gravity. However, these parameters can be insensitive. Therefore, there is a need for better methods to diagnose and monitor patients with renal disease. The use of renal biomarkers is increasing in human and veterinary medicine for the diagnosis and monitoring of acute and chronic kidney diseases. An ideal biomarker would identify site and severity of injury, and correlate with renal function, among other qualities. This article will review the advantages and limitations of renal biomarkers that have been used in dogs and cats, as well as some markers used in humans that may be adapted for veterinary use. In the future, measuring a combination of biomarkers will likely be a useful approach in the diagnosis of kidney disorders.

Radiographic contrast-media-induced acute kidney injury: pathophysiology and prophylactic strategies

Contrast-induced acute kidney injury (CI-AKI) is one of the most widely discussed and debated topics in cardiovascular medicine. With increasing number of contrast-media- (CM-) enhanced imaging studies being performed and growing octogenarian population with significant comorbidities, incidence of CI-AKI remains high. In this review, pathophysiology of CI-AKI, its relationship with different types of CM, role of serum and urinary biomarkers for diagnosing CI-AKI, and various prophylactic strategies used for nephroprotection against CI-AKI are discussed in detail.

Clinical pharmacology of furosemide in neonates: a review

Furosemide is the diuretic most used in newborn infants. It blocks the Na⁺-K⁺-2Cl⁻ symporter in the thick ascending limb of the loop of Henle increasing urinary excretion of Na⁺ and Cl⁻. This article aimed to review the published data on the clinical pharmacology of furosemide in neonates to provide a critical, comprehensive, authoritative and, updated survey on the metabolism, pharmacokinetics, pharmacodynamics and side-effects of furosemide in neonates. The bibliographic search was performed using PubMed and EMBASE databases as search engines; January 2013 was the cutoff point. Furosemide half-life (t_1/2) is 6 to 20-fold longer, clearance (Cl) is 1.2 to 14-fold smaller and volume of distribution (Vd) is 1.3 to 6-fold larger than the adult values. t_1/2 shortens and Cl increases as the neonatal maturation proceeds. Continuous intravenous infusion of furosemide yields more controlled diuresis than the intermittent intravenous infusion. Furosemide may be administered by inhalation to infants with chronic lung disease to improve pulmonary mechanics. Furosemide stimulates prostaglandin E2 synthesis, a potent dilator of the patent ductus arteriosus, and the administration of furosemide to any preterm infants should be carefully weighed against the risk of precipitation of a symptomatic patent ductus arteriosus. Infants with low birthweight treated with chronic furosemide are at risk for the development of intra-renal calcifications.

Serum and urine acute kidney injury biomarkers in asphyxiated neonates

BACKGROUND

We evaluated serum (s) cystatin C (CysC) and neutrophil gelatinase-associated lipocalin (NGAL) and urine (u) CysC, NGAL and kidney injury molecule-1 (KIM-1) as markers of acute kidney injury (AKI) in asphyxiated neonates.

METHODS

AKI biomarkers were measured in 13 asphyxiated neonates born at ≥ 36 weeks gestational age (eight with AKI and five without AKI) and 22 controls. AKI was defined as serum creatinine ≥ 1.5 mg/dl for >24 h or rising values >0.3 mg/dl from day of life (DOL) 1. Biomarkers were measured on DOL 1, 3, and 10.

RESULTS

Asphyxiated neonates had significantly higher sCysC on DOL 1 as well as sNGAL and uCysC and uNGAL (standardized to urine creatinine and absolute values) than controls at all time points. Compared to controls, significantly higher sNGAL, uCysC, and uNGAL values were observed in the asphyxia-AKI and asphyxia-no AKI subgroups. Regarding uKIM-1, only the absolute values were significantly higher in asphyxiated neonates (DOL 10). sNGAL, uCyst, and uNGAL had a significant diagnostic performance as predictors AKI on DOL 1.

CONCLUSIONS

sNGAL, uCysC, and uNGAL are sensitive, early AKI biomarkers, increasing significantly in asphyxiated neonates even in those not fulfilling AKI criteria. Their measurement on DOL 1 is predictive of post-asphyxia-AKI.

Acute kidney injury post neonatal asphyxia

Acute kidney injury (AKI) is a common consequence of perinatal asphyxia, occurring in up to 56% of these infants. A major difficulty in diagnosing this condition is the lack of a consensus definition of neonatal AKI, largely because of a dearth of specific measurable variables and biochemical markers. This review will discuss the current evidence regarding the epidemiology, investigation, and treatment of AKI in the asphyxiated neonate. Particular emphasis will be given to the investigation of renal function in the neonate and to potential biomarkers that may aid the clinician in the diagnosis of renal injury in this population.

Utility of urine myoglobin for the prediction of acute renal failure in patients with suspected rhabdomyolysis: a systematic review

BACKGROUND

Urine myoglobin continues to be used as a marker of rhabdomyolysis, particularly to assess risk of developing acute renal failure and evaluate treatment success. We sought to determine the predictive validity of urine myoglobin (uMb) for acute renal failure (ARF) in patients with suspected rhabdomyolysis.

METHODS

We performed a broad systemic review of the literature from January 1980 to December 2006 using the search terms myoglobin$ AND (renal OR ARF OR kidney). Only primary studies published in English where uMb measurement was related to ARF were included.

RESULTS

Of 1602 studies screened, 52 met all selection criteria. The studies covered a wide spectrum of etiologies for rhabdomyolysis, dissimilar diagnostic criteria for ARF and rhabdomyolysis, and various methods of uMb measurement and were mostly case series (n = 32). There was poor reporting on the uMb method, and 17 studies failed to provide any information about the method. The reporting of clinical criteria for ARF with respect to timing, description, performance, and interpretation also lacked adequate detail for replication. Eight studies (total 295 patients) had data for 2-by-2 tables. Sensitivity of the uMb test was 100% in 5 of the 8 studies, specificity varied widely (15% to 88%), and CIs around these measures were high. Pooling of data was not possible because of study heterogeneity.

CONCLUSIONS

There is inadequate evidence evaluating the use of uMb as a predictor of ARF in patients with suspected rhabdomyolysis.

Can urinary excretion rate of malondialdehyde, uric acid and protein predict the severity and impending death in perinatal asphyxia?

BACKGROUND

Perinatal asphyxia (PA) associated with multi-organ damage is a leading cause of neonatal mortality and morbidity. We evaluated if urinary malondialdehyde:creatinine (UMDA:Cr), uric acid:creatinine (UUA:Cr) and protein:creatinine (UP:Cr) vary with the severity of PA and if these parameters can predict the impending death in PA.

METHODS

Study included 20 asphyxiated and 20 healthy newborn males. Hypoxic-ischemic encephalopathy (HIE) staging, APGAR (activity, pulse, grimace, appearance and respiration) score and urinary protein, uric acid, creatinine and MDA were evaluated.

RESULTS

UMDA:Cr, UUA:Cr and UP:Cr were significantly higher and correlated with APGAR and HIE in PA. By regression analysis also, urinary parameters were found to have significant association with HIE stage and APGAR in PA. Receiver operating characteristics (ROC) curve of UP:Cr, UUA:Cr and UMDA:Cr showed area under curve of 0.896 (p=0.003), 0.859 (p=0.008) and 0.849 (p=0.010) with cut-off value of 9.04 mg, 2.34 mg and 3.49 microg/mg of creatinine respectively that can optimally predict the impending death in PA. SDS-PAGE of unconcentrated urine detected both high (73 kDa and 68 kDa) and low molecular weight proteins (52 kDa, 47 kDa, 25 kDa and 20 kDa) in PA but not in controls.

CONCLUSION

Urinary excretion rate of uric acid, MDA and proteins is higher and has potential to act as biochemical markers for severity evaluation and death prediction in PA.

Biomarkers of acute kidney injury

Acute kidney injury (AKI) is a common condition with a high risk of death. The standard metrics used to define and monitor the progression of AKI, such as serum creatinine and blood urea nitrogen levels, are insensitive, nonspecific, and change significantly only after significant kidney injury and then with a substantial time delay. This delay in diagnosis not only prevents timely patient management decisions, including administration of putative therapeutic agents, but also significantly affects the preclinical evaluation of toxicity thereby allowing potentially nephrotoxic drug candidates to pass the preclinical safety criteria only to be found to be clinically nephrotoxic with great human costs. Studies to establish effective therapies for AKI will be greatly facilitated by two factors: (a) development of sensitive, specific, and reliable biomarkers for early diagnosis/prognosis of AKI in preclinical and clinical studies, and (b) development and validation of high-throughput innovative technologies that allow rapid multiplexed detection of multiple markers at the bedside.

[Acute renal failure in full term neonates with perinatal asphyxia. Prospective study of 87 cases]

BACKGROUND

Renal involvement is frequent in neonates with perinatal asphyxia. It is correlated with the severity of neurological damage and seems to worsen the long-term neurological outcome.

PURPOSE

The aim of this study was to determine the incidence of renal failure after perinatal asphyxia, to precise the relationship between severity of cerebral damage and renal failure and to evaluate the place of renal damage in the short- and middle-term neurological outcome.

POPULATION AND METHODS

We conducted a prospective study including 87 full-term neonates admitted in the neonatology department of F. Hached university hospital in Sousse (Tunisia) and suffering from hypoxic ischemic encephalopathy from 1st January 2003 to 30 June 2005. Renal function was assessed by measuring plasma urea and creatinine at age 48 h. Renal failure was defined by a level of creatinine above 90 micromol/l. Neurologic examination was performed on day 7. The survivors were followed up by the same senior after discharge.

RESULTS

During the study period, 87 full-term neonates were admitted for hypoxic ischemic encephalopathy. The degree of neurological impairment was determined according to Sarnat classification: 1st stage 9 neonates (10,3%), 2nd stage 67 (77%) and 3rd stage 11(12,6%). Renal failure involved 15 neonates (17,2%) of whom 10 belonging to the 2nd stage group. Renal function outcome was favorable in all survivors with normalisation of plasma creatinine level between day 5 and day 15. Eight neonates died, of whom 3 with renal failure. Neurologic examination was abnormal in 36 out of 72 (50%) neonates without renal failure and in 9 of the 12 (75%) survivors with renal failure. Among the 12 neonates with renal failure, 7 had abnormal neurologic features at discharge. Neurologic assessment between 6 and 18 months was abnormal in 4/12 (33%) of neonates with renal failure versus 8/72(11%) of neonates without renal failure.

CONCLUSION

Transient renal failure is commonly observed in perinatal asphyxia. Renal failure is correlated with neurologic severity. Renal function assessment using creatinine plasma level seems to be correlated with neurologic outcome. However, other tools appreciating renal function, namely tubular function, should be determined earlier in order to predict neurologic outcome after hypoxic ischemic encephalopathy.

Biomarkers of nephrotoxic acute kidney injury

Acute kidney injury (AKI) is a common condition with significant associated morbidity and mortality. Epidemiologic data suggest that a significant proportion of AKI cases is at least partially attributable to nephrotoxin exposure. This is not surprising given intrinsic renal susceptibility to toxicant-induced injury, a consequence of the unique physiologic and biochemical properties of the normally functioning kidney. A number of pathophysiologic mechanisms have been identified that mediate toxic effects on the kidney, resulting in a variety of clinical syndromes ranging from subtle changes in tubular function to fulminant renal failure. Unfortunately, standard metrics used to diagnose and monitor kidney injury, such as blood urea nitrogen and serum creatinine, are insensitive and nonspecific, resulting in delayed diagnosis and intervention. Considerable effort has been made to identify biomarkers that will allow the earlier diagnosis of AKI. Further characterization of these candidate biomarkers will clarify their utility in the setting of acute nephrotoxicity, define new diagnostic and prognostic paradigms for kidney injury, facilitate clinical trials, and lead to novel effective therapies.

Low adjusted serum ionized calcium concentration shortly after birth predicts poor outcome in neonatal hypoxic-ischemic encephalopathy

AIM

Hypoxic-ischemic reperfusion injury causes either necrosis or apoptosis, and the influx of ionized calcium into cells is the major cause of both types of cell death. The aim of this study was to investigate whether or not the serum ionized calcium concentration in neonates with hypoxic-ischemic encephalopathy (HIE) could be used to predict their outcome.

METHODS

Serum samples were obtained shortly after birth from 20 HIE neonates who had not urinated or received treatment with calcium. Serum ionized calcium concentrations were adjusted for pH using a correction formula. Twelve neonates without any disease were selected as a control. The results were compared between nine HIE neonates who made a full recovery, 11 who died or had neurologic deficits, and 12 normal neonates.

RESULTS

Considered together, the two HIE groups had lower serum ionized calcium concentrations (1.05 +/- 0.10 mmol/L) than the control group (1.22 +/- 0.07 mmol/L; P < 0.0001). Moreover, serum ionized calcium concentrations in the group with the poor outcome (0.99 +/- 0.07 mmol/L) were lower than those in the group that made a full recovery (1.13 +/- 0.06 mmol/L; P=0.0016).

CONCLUSIONS

The serum ionized calcium concentrations shortly after birth were significantly lower in neonates with HIE who had a poor outcome. Low concentrations may reflect multiple organ damage, particularly involving the brain.

Management of acute and chronic renal failure in the newborn

Acute renal failure may be caused by a failure of renal perfusion (pre-renal failure), damage to the renal parenchyma (intrinsic renal failure) or obstruction of the urinary tract (post-renal failure). Most cases of intrinsic renal failure in the newborn are due to asphyxia, often in combination with sepsis and nephrotoxic drugs. Persistent elevation of the plasma creatinine concentration above 132.5 micromol/l (1.5mg/dl) is widely accepted as a diagnostic criterion. Oliguria or anuria may occur but is not always present. Post-renal failure is diagnosed by renal ultrasonography and is treated by relief of the obstruction. Pre-renal and post-renal failure can be distinguished by an analysis of urinary indices, especially the fractional sodium excretion, and by the response to fluid replacement. The conservative management of intrinsic renal failure includes careful attention to fluid balance, maintenance of adequate nutrition and prevention or correction of hyperkalemia, acidosis and hyperphosphatemia. Severe cases may require dialysis: peritoneal dialysis is used in most cases, but extracorporeal methods, including intermittent hemodialysis, hemofiltration and hemodiafiltration, are possible. Congenital chronic renal failure, usually caused by renal dysplasia with or without obstruction, presents in a manner similar to that of acute renal failure, with a progressive deterioration of plasma biochemical values. Dialysis is rarely necessary in the newborn period. The conservative management of chronic renal failure is similar to that of acute renal failure, with particular emphasis on nutrition, control of acidosis and the prevention of renal osteodystrophy by the use of dietary phosphate binders and vitamin D analogs.

Evaluation of renal glomerular and tubular functional and structural integrity in neonates

BACKGROUND

Renal cells are not fully differentiated at birth, representing a major risk in preterm infants. We evaluated glomerular and tubular functional integrity as well as structural integrity of renal tubules among healthy full-term and preterm infants as well as diseased preterm infants.

METHODS

A total of 50 newborns (10 healthy full-term, 10 healthy preterm, and 30 diseased preterm, at 38.9 +/- 1.10, 34.2 +/- 0.92, and 32 +/- 2.47 weeks gestational age, respectively) were included in the present study. Glomerular function was assessed by measuring urinary levels of both microalbumin and immunoglobulin G as well as serum creatinine levels, whereas the proximal tubular function was investigated by measuring the urinary levels of both alpha1-microglobulin and beta2-microglobulin as well as retinol-binding protein. Also, distal tubular reabsorption capacity was investigated by assessing fractional excretion of sodium. Moreover, the structural integrity of renal proximal tubules was studied by measuring the urinary activities of both the brush-border membrane enzyme leucine-aminopeptidase (LAP) and the lysosomal enzyme N-acetyl-beta-D-glucosaminidase. The preceding investigations were done on both the first and third days of life of all 50 newborns.

RESULTS

Glomerular and tubular function and structure was relatively impaired at birth among both healthy and diseased preterm as well as healthy full-term neonates and improved rapidly thereafter. The diseased preterm neonates showed worse renal function and structure with minimal improvement regardless of the underlying sickness.

CONCLUSION

Renal insufficiency and renal immaturity could be evaluated using enzymuria and low- and high-molecular-weight proteinuria as noninvasive methods.

Netilmicin effect on urinary retinol binding protein (RBP) and N-acetyl-beta-D-glucosaminidase (NAG) in preterm newborns with and without anoxia

The study aim was to evaluate urinary excretion of Retinol Binding Protein (RBP), compared with urinary excretion of N-acetyl-beta-D-glucosaminidase (NAG), in preterm infants with anoxia and netilmicin treatment. Urinary RBP and NAG were evaluated in 83 preterm newborns divided in 4 groups: 37 healthy preterm newborns (controls); 14 with neonatal anoxia; 16 treated with ampicillin + netilmicin; 16 with neonatal anoxia and treated with ampicillin + netilmicin. RBP was determined by an automated nephelometric technique and NAG by a colorimetric method on 5-h urine samples in the first week of life. Results showed that urinary excretion of RBP (average from first week values) was 1.06+/-0.67 g/mol creatinine (mean +/- SD) in controls, 1.99+/-1.41 in antibiotic-treated newborns, 3.99+/-4.57 in anoxic newborns and 3.75+/-3.48 in anoxic newborns under antibiotic treatment. When gestational age was not considered, a marked effect of anoxia (P<0.001) and a borderline effect of netilmicin (P<0.059) on RBP excretion were detected by ANOVA. However when gestational age was also considered by analysis of covariance, it appeared as the strongest predictor of RBP excretion (P<0.001), while the effect of netilmicin was no longer significant (P=0.181). The effect of anoxia persisted, although less remarkable (P=0.010). Conversely anoxia did not affect urinary NAG excretion, which was rather correlated with gestational age and netilmicin administration. The authors conclude that RBP and NAG urinary excretion may be used to discriminate between neonatal anoxia and netilmicin treatment, respectively as etiologic factors of renal tubular damage in the newborn.

Antibacterial-induced nephrotoxicity in the newborn

Antibacterials are the primary cause of drug-induced kidney disease in all age groups and these agents bring about renal damage by 2 main mechanisms, namely, direct and immunologically mediated. For some antibacterials (aminoglycosides and vancomycin) nephrotoxicity is very frequent but generally reversible upon discontinuation of the drug. However, the development of acute renal failure with these agents is possible and its incidence in the newborn seems to be increasing. Antibacterials are very often used in the neonatal period especially in very low birthweight neonates. The role of neonatal age in developing nephrotoxicity has still to be defined. Since the traditional laboratory parameters of nephrotoxicity are abnormal only in the presence of substantial renal damage, the identification of early non-invasive markers of the renal damage (urinary microglobulins, enzymes and growth factors) is of importance. Aminoglycosides and glycopeptides are still frequently used, either alone or in combination, despite their low therapeutic index. Numerous factors intervene in bringing about the kidney damage induced by these 2 classes of antibacterials, such as factors related to the antibacterial itself and others related to the associated pathology as well as pharmacological factors. Nephrotoxicity can be caused by the beta-lactams and related compounds. Their potential to cause nephrotoxicity decreases in the order: carbapenems > cephalosporins > penicillins > monobactams. Third generation cephalosporins are frequently used in neonates. However, they are well tolerated compounds at the renal level. The nephrotoxicity of other classes of antibacterials is not discussed either because they are only used in neonates in exceptional circumstances, for example, chloramphenicol and cotrimoxazole (trimethoprim-sulfamethoxazole) or are not associated with significant nephrotoxicity, for example macrolides, clindamicin, quinolones, rifampicin (rifampin) and metronidazole. Antibacterial-induced nephrotoxicity is an important parameter to be considered when treating the newborn and this is particularly true when use of a combination of different antibacterials and/or drugs with a nephrotoxic potential is being considered. However, other parameters, such as antibacterial spectrum, pharmacokinetics, post-antibacterial effect, clinical efficacy, general adverse effect profile and cost, must also be considered in the choice of antibacterial therapy in the neonate. Knowledge of the renal safety of antibacterials and the correct approach to therapeutic drug monitoring may be useful elements for preventing iatrogenic renal disorders.

Indices of renal tubular function in perinatal asphyxia

AIMS

To determine and compare two urinary indices of renal tubular function, N-acetyl-glucosaminidase (NAG) and beta 2-microglobulin (beta 2 M), in healthy term neonates and babies with perinatal asphyxia.

METHODS

In a prospective case-control study using asphyxiated (n = 35) and normal control (n = 55) infants, urinary NAG and beta 2 M were assayed at 24-48 hours of life, 4-6 days, and 4-6 weeks.

RESULTS

NAG and beta 2 M were significantly increased at 24-48 hours and 4-6 days in the asphyxiated infants compared with the controls. Increased NAG values reflect the degree of perinatal asphyxia more than do beta 2 M. Gentamicin also increased NAG excretion, but to a lesser extent than did perinatal asphyxia.

CONCLUSIONS

NAG (+/- beta 2 M) may be a useful marker of perinatal asphyxia. Urinary NAG concentrations correlate with the severity of perinatal asphyxia.

Measurement of albumin and low molecular weight proteins in the urine of newborn infants using a cotton wool ball collection method

OBJECTIVE

The aim of this study was to investigate the inter-relationship between urinary excretion of alpha-1-microglobulin (A1M), retinol-binding protein (RBP) and albumin in term and premature neonates, with urine collected into cotton wool balls and extracted by a novel method.

SUBJECTS AND METHODS

Sixty-four infants were studied on the first day of life; 26 had been born at term (37-42 weeks gestation) and 38 prematurely (24-28 weeks n = 16, 29-36 weeks n = 22). Urine collected into cotton wool balls was analysed following a new detergent extraction method, which resulted in a recovery rate of 94-107% for albumin. A1M, RBP and creatinine.

RESULTS

Urinary protein excretion, expressed as a ratio to urinary creatinine, decreased significantly with increasing gestational age (24-28 weeks, 29-36 weeks, 37-42 weeks: albumin:creatinine ratio mg/mmol mean 96.9, 31.7, 19.3; A1M:creatinine ratio mg/mmol mean 99.3, 37.0, 7.8; RBP:creatinine ratio mg/mmol mean 16.2, 3.8, and < 0.01, below the limit of detection, respectively). When results were corrected for birthweight, this gestation-associated effect was still present for A1M and RBP, but not for albumin. In premature infants there was a significant positive correlation between A1M:creatinine ratio and RBP:creatinine ratio (r = 0.85), and also between albumin and both A1M and RBP (r = 0.82 and 0.77).

CONCLUSION

Increased excretion of A1M, RBP and albumin at earlier gestational ages is probably due to proximal tubular immaturity, although tubular damage and also glomerular dysfunction cannot be excluded as possible explanations.

Nonoliguric and oliguric acute renal failure in asphyxiated term neonates

The purpose of this study was to determine the prevalence and types of acute renal failure in asphyxiated full-term neonates and to evaluate the accuracy of an asphyxia morbidity score in predicting acute renal failure. Neonates admitted to one institution from 1990 through 1993 with a gestational age > or = 36 weeks and 5-min Apgar score < or = 6, without congenital malformations or sepsis, were studied retrospectively for acute renal failure in the 1st week of life. Acute renal failure was defined as serum creatinine > 1.5 mg/dl (133 mumol/l) with normal maternal renal function. Nonoliguric renal failure was defined as renal failure with urine output > 1 ml/kg per hour after the 1st day. An asphyxia morbidity scoring system was used to distinguish severe from moderate asphyxia. The score ranged from 0 to 9 and was based upon fetal heart rate, Apgar score at 5 min, and base deficit in the 1st h of life. The score for severe asphyxia was defined as 6-9 and for moderate asphyxia as 1-5. Sixty-six neonates fulfilled study criteria. Acute renal failure was present in 20 of 33 (61%) infants with severe asphyxia scores and 0 of 33 with moderate asphyxia scores (P < 0.0001). Acute renal failure was nonoliguric in 12 of 20 (60%), oliguric in 5 of 20 (25%) and anuric in 3 of 20 (15%). In conclusion 1) acute renal failure occurred in 61% of infants with severe asphyxia, 2) acute renal failure associated with severe asphyxia was predominantly nonoliguric and 3) an asphyxia morbidity score, which can be determined at 1 h of age, predicted acute renal failure in full-term infants with 100% sensitivity and 72% specificity.

Multiple organ involvement in perinatal asphyxia

OBJECTIVES

(1) To evaluate the frequency and spectrum of severity of multisystem dysfunction after perinatal asphyxia and (2) to analyze the relationship between the clinical and biochemical markers of perinatal asphyxia and multiorgan involvement.

STUDY DESIGN

Seventy-two consecutive term newborn infants with perinatal asphyxia were studied prospectively. Systematic neurologic, renal, pulmonary, cardiac, and gastrointestinal evaluations were performed. Involvement of each organ was classified as moderate or severe.

RESULTS

Involvement of one or more organs occurred in 82% of the infants; the central nervous system (CNS) was most frequently involved (72%). Severe CNS injury (7 infants) always occurred with involvement of other organs, although moderate CNS involvement was isolated in 14 infants. Renal involvement occurred in 42%, pulmonary in 26%, cardiac in 29%, and gastrointestinal in 29% of the infants; 15% neonates had renal failure and 19% had respiratory failure. The Apgar scores at 1 and 5 minutes were the only perinatal factors related to the number of organs involved and the severity of involvement; the Apgar score at 5 minutes had the stronger independent association. No relationship or organ dysfunction was found with the umbilical cord arterial blood pH, meconium-stained amniotic fluid, umbilical cord abnormalities, presentation, or type of delivery.

CONCLUSIONS

Our findings indicate that the Apgar score at 5 minutes, in infants who have other criteria for asphyxia, is the perinatal marker that may best identify infants at risk of organ dysfunction.

Characterization of renal tubular damage in preterm infants with renal failure

This study attempts to clarify the characteristics of renal tubular damage in preterm infants with renal failure. Sixty-one neonates (17 term and 44 preterm infants) were divided into three groups: 15 infants with intrinsic renal failure (IRF), five term and 10 preterm; 19 with pre-renal renal failure (PRF), five term and 14 preterm; and 27 without renal dysfunction (control), seven term and 20 preterm. Urine was collected for an 8 h period on the 2nd or 3rd day of life to determine the following parameters: creatinine clearance (Ccr), fractional excretion of sodium (FENa), urinary N-acetyl-beta-D-glucosaminidase (NAG) index and endothelin-1 (ET-1) excretion. Parameters of renal tubular function and/or renal tubular damage such as FENa, NAG index and ET-1 excretion were considered as a useful marker to differentiate IRF from PRF in preterm infants. However, these parameters were significantly elevated in preterm infants with PRF. These findings led us to make the following speculations: (i) renal tubular damage may easily occur in preterm infants; and (ii) there still remains difficulty in differentiation between IRF and PRF using Ccr instead of the fluid challenge test.

Assessment of retinol-binding protein excretion in normal children

Retinol-binding protein (RBP) is a low molecular weight protein freely filtered at the glomerulus. The fractional tubular reabsorption of RBP is 99.97% and increased excretion is therefore a sensitive marker of tubular dysfunction. We obtained early-morning urine specimens from 151 well children, from newborn to 16 years of age. RBP was measured using an enzyme-linked immunosorbent assay, albumin by a radioimmunoassay and creatinine by a modified Jaffé reaction. Protein excretion was assessed by calculating the protein:creatinine ratio for early-morning urine samples. We found a fall in both RBP and albumin excretion with increasing age, particularly in the 1st year of life, with a much wider variation in values from the infants studied. The mean excretion of RBP for children aged 0-6 months [51.4 (0.6-4,719) micrograms/mmol] was significantly higher (P < 0.001) than the mean for children aged 6 months to 16-years [15.0 (3.8-60) micrograms/mmol]. It has been shown that measurement of tubular proteinuria using the RBP: creatinine ratio is useful in the assessment of children with renal disease and we propose a value two standard deviations above the geometric mean for the age of the patient as an upper limit of normal.

Evaluation of diagnostic criteria of acute renal failure in premature infants

A prospective study was performed to investigate the validity of renal failure index (RFI) or fractional excretion of sodium (FENa) in preterm infants. The subjects were 128 newborn infants, 72 with oliguria and 56 without renal dysfunction (control). Oliguric infants were divided into two categories: acute renal failure (ARF) and prerenal failure (PRF), according to creatinine clearance (Ccr). Furthermore, all subjects were divided into four groups according to gestation, that is, 38 infants with gestational age of 25-28 weeks (group 1), 28 with 29-30 weeks (group 2), 38 with 31-36 weeks (group 3) and 24 of > 37 weeks (group 4). As a result, differentiation between ARF and PRF was valid when the RFI or FENa was used in infants of > 29 weeks gestation (groups 2, 3 and 4). Although infants of > 31 weeks gestation (groups 3 and 4) who present with an RFI > 3 or an FENa > 3% may be diagnosed as having ARF, infants in group 2 with an RFI of > 8 or an FENa of > 6% may be diagnosed as having ARF. For the infants in group 1, the application of RFI or FENa for diagnosis of ARF may be limited because of some overlap among the groups.

Low molecular weight proteins in children with renal disease

Low molecular weight proteins are of interest in children because their increased urinary excretion is a sign of renal tubular disease and their increased plasma concentration is inversely related to glomerular filtration rate. These proteins include beta 2-microglobulin (B2M), retinol-binding protein (RBP), alpha 1-microglobulin (A1M) and lysozyme. B2M is unstable in acid urine, in contrast to RBP and A1M which are more stable. Any increase in the urinary excretion of B2M or RBP is highly specific for tubular disease, whereas increased excretion of A1M may be seen with glomerular proteinuria. Areas of clinical application include tubular and glomerular diseases, detection of drug toxicity, reflux nephropathy, birth asphyxia and insulin-dependent diabetes mellitus. Methods of sample collection and analysis of these proteins are discussed.

Renal function in very low birth weight infants: normal maturity reached during early childhood

Development of glomerular and tubular renal function is delayed in preterm infants. To study the pattern of maturation during infancy and childhood, we re-evaluated renal function in 22 very low birth weight infants--in 14 of the infants at 18 months postconceptional age (9 months corrected age) and in the remaining 8 infants at 8 years of age. The glomerular filtration rate remained lower at 9 months corrected age than in term infants of the same postconceptional age: 82 +/- 23 versus 125 +/- 18 ml/min per 1.73 m2 (p < 0.001). At 8 years of age the glomerular filtration rate did not differ from that of healthy control subjects. Effective renal plasma flow, filtration fraction, albumin excretion, maximal concentrating ability, and kidney size determined by ultrasonography were all normal at 8 years of age. We conclude that renal function, which is markedly reduced during the neonatal period in very low birth weight infants, reaches normal maturity by 8 years of age but not by 9 months corrected age.

Assay of N-acetyl-beta-D-glucosaminidase in urine from neonates: comparison of two new colorimetric methods using MNP-GlcNAc and VRA-GlcNAc as substrates

The NAG activity present in urine from newborn babies was assayed using two colorimetric procedures with either MNP-GlcNAc or VRA-GlcNAc as substrate and compared with data obtained with the well established PNP-GlcNAc procedure. Both new assays were easy to perform and reproducible. The MNP-GlcNAc method has the advantage that it is now available as a kit; however, the VRA-GlcNAc procedure is more sensitive. NAG activity, creatinine concentration and NAG-index values were determined in normal neonates and within-run imprecision calculated. Excellent correlations were found between MNP-GlcNAc-ase and VRA-GlcNAc-ase indices (r = 0.984) and between PNP-GlcNAc-ase and VRA-GlcNAc-ase indices (r = 0.952). When low molecular weight urinary components were removed by gel filtration no significant change in VRA-GlcNAc-ase activity was observed.

Salt and the newborn kidney

Renal function differs in term infants from that in adults, with lower glomerular filtration rate (GFR) and reduced proximal tubular reabsorption of sodium (Na) and water: nevertheless, it is adequate for their needs. This is not true of very preterm infants in whom hyponatraemia is common. Animal studies have shown that Na+, K(+)-ATPase and the Na+/K+ exchanger are poorly expressed at birth with rapid postnatal rises. Cell receptors for hormones that influence tubular Na transport are less numerous in the premature infant than later in life: intracellular second messenger systems may also be immature. The low GFR is due to vasoconstriction and may be necessary to prevent water and electrolyte wasting due to tubular overload. The hyponatraemia of prematurity could, in principle, be due either to Na loss or water excess and can be prevented either by giving additional Na or by restricting water intake. Na supplementation causes relative volume expansion (VE), water restriction volume contraction (VC); this is demonstrated by the effect of the two approaches on weight gain and on the levels of vasoactive hormones in the blood. We argue that moderate VE is more physiological than VC, both in attempting to simulate intrauterine conditions and in consideration of the infant's nutritional needs. The much less common complication of hypernatraemia is usually due to abnormal water loss and should be prevented by increasing water intake appropriately. The above applies to well, preterm babies: sick preterm infants are much more variable in their Na and water requirements than well infants of comparable gestation and weight and each needs an individually tailored regimen based on frequent clinical assessment and laboratory measurement.