Serum Creatinine and Fat-free Mass (Lean Body Mass)

Serum creatinine is widely used as an index of glomerular filtration rate (GFR) (1). However, it is not a sensitive index because GFR may have to decrease by >50% before serum creatinine becomes “abnormal”, and this may be at least partly attributable to the wide reference interval for serum creatinine (44–124 μmol/L). One of the factors influencing the creatinine concentration is said to be muscle mass (1)(2). Thus, it can be argued that if the reference interval for serum creatinine can be adjusted for muscle mass, serum creatinine may be a better index of GFR. However, there is little information on the relationship between muscle mass and serum creatinine. We previously have shown that the contribution of lean body mass (LBM) to the variation in serum creatinine in healthy subjects is small (3). In this report, we extend these observations to another group and used a more precise method to measure LBM.