To the Editor.—
We enjoyed Dr Gifford's article entitled "Isolated Systolic Hypertension in the Elderly" (1982;247:781). We would like to comment, however, on his statement that "serum creatinine level estimates renal function." With the decline in lean body mass with age, daily endogenous creatinine production decreases. Therefore, creatinine clearance must fall to a greater extent in the elderly before the serum creatinine level increases. This has recently been emphasized by Ouslander1 in a review of drug therapy in the elderly. The serum creatinine level may fall within the normal range in an elderly patient who has notable impairment of his renal function.2 A useful nomogram to estimate creatinine clearance in relation to age has been devised3: creatinine clearance = [(140-age) × body weight, kg]/[72 × serum creatinine] (multiply by 0.85 for females).This estimation is especially important when prescribing any medication that is eliminated by the kidney.
Hering PJ, Carlson RE. Serum Creatinine and Renal Function in the Elderly. JAMA. 1982;248(1):31. doi:10.1001/jama.1982.03330010015013