Laboratory tests of renal function

Reliable laboratory tests for renal function are important for (a) the early recognition of perioperative renal failure; (b) helping to detect and monitor renal disease and; (c) calculating dose adjustments in prescribing for patients with renal failure. Assessment of renal function usually involves urinalysis and some estimate of glomerular function. The glomerular filtration rate is possibly the single most important marker of renal function. Taking serial measurements of creatinine clearance is still the most sensitive test for predicting perioperative renal failure. Raised serum urea and creatinine levels are late signs of renal dysfunction and are also influenced by many non-renal variables. Tests of renal tubular function are more complex and required less often than tests of glomerular function. Both proximal and distal tubular function can be assessed. The ability to measure renal blood flow easily and reliably will significantly improve the diagnosis of perioperative acute renal failure. However, the use of these techniques is still limited due to practical and methodological constraints. No single test of renal function should be considered without reference to the patient's clinical history and examination.