Apparent reduction of endogenous creatinine clearance by salicylate treatment.

A prospective study of nine patients with rheumatoid arthritis and 11 healthy volunteers who started salicylate treatment showed that in 18 of the 20 subjects creatinine clearance values fell the average being 25%. Serum creatinine concentration was increased by an average of 38%, although blood urea levels were unchanged. Since 51Cr-edetic acid clearance tests performed at the same time in 12 of the subjects were not affected, the fall in creatinine clearance was probably not due to impaired glomerular function, and salicylate ingestion may therefore invalidate the creatinine clearance test as an index of glomerular filtration rate. It is clearly important to inquire into the patient's analgesic comsumption when using the creatinine clearance test to assess glomerular function.