Serum creatinine decreases with age with the decrease in lean body mass. However, the number of functioning glemeruli and kidney function decrease with age as well, making the creatinine an unreliable indicator of renal function in older adults.
The solution? Calculate the creatinine clearance (CrCl) (or GFR) for a more accurate assessment of the renal function. You can use simple equations such as the Cockroft-Gault equation which incorporate the body weight and age.
CrCl (mL/min) = (140-age) x lean body weight (kg) x (0.85 if female)
serum creatinine (mg/dL) x 72
References
Cockcroft DW, Gault H, Gault MH. Prediction of creatinine clearance from serum creatinine. Nephron. 1976;16(1):31-41. doi:10.1159/000180580.
Wiggins J, Patel SR. Aging of the kidney. In: Halter J, Ouslander J, Studenski S, et al., eds. Hazzard’s Geriatric Medicine and Gerontology. 7th edition. New York, NY: McGraw-Hill; 2017. http://accessmedicine.mhmedical.com/content.aspx?bookid=1923§ionid=144525776.
