Increased levels of urinary adenosine deaminase binding protein in children treated with cisplatin or methotrexate

Nephroscreen™: a diagnostic test for predicting acute renal failure?

Acute renal failure is a frequent and often fatal complication of hospitalized patients. While the risk of acute renal failure among select patient groups is well recognized, physicians currently rely on diagnostic tests such as changes of serum creatinine and indirect assessment of the glomerular filtration rate to diagnose acute renal failure. Although these parameters capture the degree of kidney function lost, they are not warning signs of evolving kidney injury. While the clinical emergence of acute renal failure is sudden, the pathologic changes preceding loss of kidney function are not so sudden. Nephroscreen is a fast and easy-to-use urine enzyme-linked immunosorbent assay test designed to quantify specific pathologic events preceding death of renal proximal tubule cells. It detects acute kidney damage days before serum creatinine rises and may open new avenues to defining acute renal failure as well as treating acute renal failure patients earlier and more effectively.

Diagnosis, epidemiology and outcomes of acute kidney injury

Acute kidney injury is an increasingly common and potentially catastrophic complication in hospitalized patients. Early observational studies from the 1980s and 1990s established the general epidemiologic features of acute kidney injury: the incidence, prognostic significance, and predisposing medical and surgical conditions. Recent multicenter observational cohorts and administrative databases have enhanced our understanding of the overall disease burden of acute kidney injury and trends in its epidemiology. An increasing number of clinical studies focusing on specific types of acute kidney injury (e.g., in the setting of intravenous contrast, sepsis, and major surgery) have provided further details into this heterogeneous syndrome. Despite our sophisticated understanding of the epidemiology and pathobiology of acute kidney injury, current prevention strategies are inadequate and current treatment options outside of renal replacement therapy are nonexistent. This failure to innovate may be due in part to a diagnostic approach that has stagnated for decades and continues to rely on markers of glomerular filtration (blood urea nitrogen and creatinine) that are neither sensitive nor specific. There has been increasing interest in the identification and validation of novel biomarkers of acute kidney injury that may permit earlier and more accurate diagnosis. This review summarizes the major epidemiologic studies of acute kidney injury and efforts to modernize the approach to its diagnosis.

Urinary biomarkers as a diagnostic tool for acute kidney injury

Acute kidney injury is a common condition in hospitalized patients with significant associated morbidity and mortality. Although impressive progress has been made in the understanding of the molecular and biochemical mechanisms of kidney injury, the ability to effectively treat and thus impact on the outcomes of acute kidney injury has been disappointing. One of the major reasons for this has been the reliance on current measures of renal dysfunction, such as serum creatinine and blood urea nitrogen, which are insensitive to small changes in renal function and subtle signs of kidney injury. This insensitivity of commonly used biomarkers of renal dysfunction not only prevents timely diagnosis and estimation of injury severity, but also delays administration of putative therapeutic agents. A number of serum and urinary proteins have been identified that may herald acute kidney injury prior to a rise in serum creatinine. Further characterization of these candidate biomarkers will clarify their utility and define new diagnostic and prognostic paradigms for acute kidney injury, facilitate clinical trials and lead to novel effective therapies.

Urinary excretion of adenosine deaminase binding protein in neonates treated with tobramycin

The potential tubulotoxicity of tobramycin and cefotaxim were assessed in neonates by measuring the urinary level of adenosine deaminase binding protein (ABP) and urinary alpha 1-microglobulin and beta 2-microglobulin. In a prospective study, 33 neonates who received tobramycin and cefotaxim for suspected neonatal sepsis were compared with 48 untreated newborns during the first 10 days of life. The urinary concentrations of ABP and its excretion rates, corrected for body weight and body surface area, were significantly increased from the 1st day of treatment. Urinary alpha 1-microglobulin and beta 2-microglobulin were not elevated under tobramycin and cefotaxim during the first 2 days of treatment. We conclude that ABP may be a sensitive marker for the detection of proximal renal tubular injury during tobramycin and cefotaxim treatments of neonates. The increase in urinary ABP which occurs before an elevation of urinary alpha 1-microglobulin and beta 2-microglobulin may reflect earlier structural than functional alterations. However, since none of the treated infants had signs of electrolyte disorders or glomerular dysfunction, the clinical relevance of ABP measurement should be reevaluated.

Tubular nephrotoxicity after cardiac surgery utilising cardiopulmonary bypass

Markers of renal tubular injury were examined in 21 patients (16 male, 5 female, mean age 57.4 years) undergoing cardiac surgery utilising cardiopulmonary bypass. Postoperative urine outputs were very high (200-250 ml/h at 1-2 h), decreasing to 100 ml/h by 6 h. Although creatinine clearances did not vary significantly in the postoperative period (P = 0.16), significant changes were noted in the urinary concentrations of three tubular markers relative to creatinine concentration (P < 0.001). Urinary beta 2-microglobulin increased from negligible levels (median 0.01 mg/mmol creatinine) to peak at 4 h (median 4.55 mg/mmol), in part due to interference with its reabsorption by the plasma volume expander Haemaccel. Concentrations of the brush border antigen adenosine deaminase binding protein increased 6-fold, from a median of 5.03 arbitrary units (AU)/mumol to 31.2 AU/mumol at 48 h. The lysosomal enzyme N-acetyl-beta-D-glucosaminidase increased nearly 4-fold, from 0.68 units/mmol to 2.64 units/mmol at 48 h. Our results suggest that cardiac surgery utilising cardiopulmonary bypass is associated with acute tubular injury which can occur in the absence of overt changes in creatinine clearance.

Assessment of chemotherapy-associated nephrotoxicity in children with cancer

Assessment of the toxicity caused by chemotherapy in children with cancer has become more important as the number of long-term survivors has continued to increase. It is vital to monitor both acute life-threatening adverse effects and long-term toxicity that may impair the child's development and cause permanent morbidity. Renal damage may follow treatment with cytotoxic drugs, especially cisplatin or ifosfamide, and lead to glomerular, proximal tubular or distal tubular impairment or to any combination of these. Greater understanding of nephrotoxicity and of its prevention may enable the use of more intensive schedules or of higher doses of potentially nephrotoxic chemotherapy. However, the evaluation of cytotoxic drug-induced nephrotoxicity has frequently depended mainly on measurement of the plasma creatinine concentration, which may remain normal despite substantial glomerular impairment or severe tubular dysfunction. Detailed assessment of nephrotoxicity depends on an understanding of normal renal physiology and requires evaluation of all aspects of function. A comprehensive but simple investigatory protocol that enables assessment of the nature and severity of nephrotoxicity in children is described, which can be performed without admission to hospital. Glomerular function is assessed by measurement of the glomerular filtration rate from the plasma clearance of [51Cr]-ethylenediaminetetraacetic acid ([51Cr]-EDTA). Proximal nephron function is evaluated in three ways: by measurement of the concentration of calcium, magnesium, phosphate, glucose and urate in blood and urine along with calculations of their fractional excretion and of the renal threshold for phosphate; by determination of the excretion in urine of low-molecular-weight proteins (e.g. retinol-binding protein); and by investigation of urinary bicarbonate excretion in patients who are acidotic. Distal nephron function is initially investigated by examination of the concentration (osmolality) and acidification (pH) of an early morning sample of urine. Finally, a group of general investigations is performed, including quantitation of urinary excretion of renal tubular enzymes (e.g. N-acetylglucosaminidase) and measurement of blood pressure.