Muscle mass, creatinine, cystatin C and selective glomerular hypofiltration syndromes.

In this issue of Clinical Kidney Journal , Stehlé and colleagues demonstrate that estimation of glomerular filtration rate (GFR) by use of creatinine and a measure, total lumbar muscle cross-sectional area, reflecting the total muscle mass of an individual, is superior to GFR-estimating equations based upon creatinine and demographic variables. The report by Stehlé et al. demonstrates one solution to the interference of muscle mass in the use of creatinine to estimate GFR. This interference was identified already at the start, in 1959, of using creatinine for estimation of GFR. Different ways of taking the muscle mass into account when creatinine-based estimations of GFR have been used generally include use of controversial race and sex coefficients. A new marker of GFR, cystatin C, introduced in 1979, has been shown to be virtually uninfluenced by muscle mass. In this editorial, the simultaneous use of creatinine and cystatin C to estimate GFR, muscle mass and selective glomerular hypofiltration syndromes is described.