Acute renal failure (ARF) has traditionally been defined as the abrupt loss of kidney function that results in the retention of urea and other nitrogenous waste products and in the dysregulation of extracellular volume and electrolytes. The loss of kidney function is most easily detected by measurement of the serum creatinine which is used to estimate the glomerular filtration rate (GFR).
Three problems are associated with the use of the serum creatinine to quantitatively define ARF:
- Serum creatinine does not accurately reflect the GFR in a patient who is not in steady state. In the early stages of severe acute renal failure, the serum creatinine may be low even though the actual (not estimated) GFR is markedly reduced since there may not have been sufficient time for the creatinine to accumulate. (See "Assessment of kidney function".)
- Creatinine is removed by dialysis. As a result, it is usually not possible to assess kidney function by measuring the serum creatinine once dialysis is initiated. One exception is when the serum creatinine continues to fall on days when hemodialysis is not performed, indicating recovery of renal function.
- Numerous epidemiologic studies and clinical trials have used different cut-off values for serum creatinine to quantitatively define ARF .
The lack of consensus in the quantitative definition of ARF, in particular, has hindered clinical research since it confounds comparisons between studies. Some definitions employed in clinical studies have been extremely complex with graded increments in serum creatinine for different baseline serum creatinine values [1,2]. As an example, in a classic study of the epidemiology of hospital-acquired acute renal failure, ARF was defined as a 0.5 mg/dL increase in serum creatinine if the baseline serum creatinine was ≤1.9 mg/dL, an 1.0 mg/dL increase in serum creatinine if the baseline serum creatinine was 2.0 to 4.9 mg/dL, and a 1.5 mg/dL increase in serum creatinine if the baseline serum creatinine was ≥5.0 mg/dL .
The Acute Dialysis Quality Initiative (ADQI) was created by a group of expert intensivists and nephrologists to develop consensus and evidence based guidelines for the treatment and prevention of acute renal failure . Recognizing the need for a uniform definition for ARF, the ADQI group proposed a consensus graded definition, called the RIFLE criteria . A modification of the RIFLE criteria was subsequently proposed by the Acute Kidney Injury Network, which included the ADQI group as well as representatives from other nephrology and intensive care societies [5-7].