Acute renal failure (ARF) is defined as the loss of renal function over a period of hours to days, as reflected in the glomerular filtration rate (GFR). ARF is a relatively common problem, affecting up to 5% of hospitalized patients<sup>18 Hou S.H., Bushinsky D.A., Wish J.B. , et al. Hospital-acquired renal insufficiency: A prospective study Am J Med 1983 ;  74 : 243-248  [cross-ref]

Cliquez ici pour aller à la section Références</sup> and approximately 1% of patients presenting to hospital-based emergency departments.<sup>20 Kaufman J., Dhakal M., Patel B. , et al. Community-acquired acute renal failure Am J Kidney Dis 1991 ;  17 : 191-198

Cliquez ici pour aller à la section Références</sup> ARF may have a multitude of causes, but an approach to the patient suffering from ARF by categorizing it as prerenal, intrarenal, or postrenal may benefit the clinician. Fortunately, many patients suffering from ARF fall into one of a few broad categories, each of which has a smaller range of differential diagnoses. This article discusses the differential diagnosis of ARF in a variety of commonly encountered clinical situations. Complications of ARF and their management are also discussed.

GFR, the most direct indicator of renal function, is difficult to measure, requiring the assessment of radioactive inulin or other radioisotope clearance for accurate determination. Because these studies are impractical for routine clinical care, the assessment of renal function usually depends on the use of the blood urea nitrogen (BUN) and creatinine (Cr) concentrations, both easily performed on routine serum samples, but the careful clinician must be aware of their limitations. The correlation between both of these values and GFR depends on the assumption that they are delivered to the serum from tissue at a constant rate. Conditions that alter the rate of BUN or Cr production, such as a hypercatabolic state or diminished muscle mass, affect serum levels of these molecules and thereby reduce their correlation with renal function. In general, the serum Cr, which is produced at a constant rate by muscle tissue, more accurately reflects GFR than the BUN. Corrections must be made, however, for a patient's body size and age; older patients and those with smaller frames produce less creatinine. Thus, a serum Cr of 1.7 may reflect modest renal compromise in an otherwise healthy 40-year-old man but may indicate significant renal failure in a thin 80-year-old woman. Nomograms and equations are available that accurately correlate age, ideal body weight, and Cr with GFR.<sup>11 Cockcroft D.W., Gault M.H. Prediction of creatinine clearance from serum creatinine Nephron 1976 ;  16 : 31-36  [cross-ref]

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ARF is traditionally classified into three categories, based principally on the pathophysiology of the disease. The first, prerenal ARF, is defined as a rapidly reversible rise in the serum Cr caused by renal hypoperfusion. In prerenal ARF, there is no frank parenchymal damage to the kidney; reduction in GFR merely reflects a drop in glomerular perfusion. Thus, as perfusion is restored, renal function returns rapidly to normal values with gradual reductions in the serum Cr concentration as the normal steady-state is restored. In contrast, intrarenal ARF reflects damage to the renal tissue proper. This may be due to prolonged hypoperfusion, resulting in tissue ischemia and acute tubular necrosis (ATN), or it may be due to toxic damage to the nephron, as may occur with certain drugs. Several other conditions that cause intrarenal ARF are discussed later. Finally, postrenal ARF results from the obstruction of the urinary collection system at one of several levels. Because one kidney usually has adequate functional capacity to compensate for its obstructed partner, postrenal ARF is relatively rare unless obstruction is severe, prolonged, and bilateral. Usually, it results from obstruction distal to the bladder, as by an enlarged prostate, or it occurs in patients with a single functioning kidney that becomes obstructed more proximally.

In addition to the aforementioned classification, patients with ARF may be grouped into categories based on urine output. Patients with no urine output are said to be anuric; those with less than 400 mL per 24 hours are said to have oliguric ARF, whereas those with greater than 400 mL per 24 hours have nonoliguric ARF. These distinctions are relevant because patients with nonoliguric renal failure generally have a better prognosis than those with oliguric renal failure.<sup>2 Anderson R.J., Linas S.L., Berns A.S. , et al. Nonoliguric acute renal failure N Engl J Med 1977 ;  296 : 1134-1138  [cross-ref]

Cliquez ici pour aller à la section Références</sup> Any cause of oliguric ARF may also cause nonoliguric ARF; often the presence of oliguria reflects the severity of disease rather than its cause.