Renal dysfunction. 1. Urea and creatinine.

Serum urea is more frequently increased in nonrenal than in renal disease, a fact that blunts its diagnostic usefulness. The serum creatinine is probably the most useful of commonly available tests for both detecting and monitoring renal disease, but it is not without its shortcomings. Serum urea/creatinine ratios are generally supportive of clinical impressions but are subject to so many variables as to be too tenuous for diagnostic purposes, especially in acute renal failure. Measured creatinine clearances are still widely performed but are subject to so many variables (none the least of which is inaccurate urine collection) as to warrant abandonment. Estimated creatinine clearances are reasonably accurate, but indications for their use are relatively limited.