The clinical evaluation of renal function.

Renal function tests are of limited value in differential diagnosis, except to establish the existence of uremia. The ability of the kidney to concentrate urine is often the first function to manifest impairment, but is of little value in prognosis. All clearance tests suffer a similar disability: Hypertrophy of nephrons with restoration of normal function may mask nephron loss. For the reasons outlined, the serum creatinine determination is the most useful of the clinical function tests, especially when combined with a test of maximum concentrating ability. In men, the serum creatinine value divided into 100 gives the approximate creatinine clearance; in women the numerator must be 60. For greater precision, the actual creatinine clearance should be determined. Finally, frequent serial determinations of any of the function tests offer prognostic utility greater than do infrequently performed research methods.