Relationships among serum cystatin C, serum creatinine, lean tissue mass and glomerular filtration rate in healthy adults

In an effort to increase our knowledge of the optimal use of serum cystatin C and creatinine as glomerular filtration rate (GFR) markers, these variab les, as well as lean tissue mass and GFR, were determined in a population o f 42 healthy young adults (men and women with normal GFR). Dual-energy X-ra y absorptiometry and measurement of the plasma clearance of iohexol were us ed to measure lean tissue mass and GFR, respectively. Serum creatinine was significantly correlated to lean tissue mass (r = 0.65; p < 0.0001) but not to GFR (1/creatinine vs. GFR: r = 0.11; p = 0.106). In contrast, serum cys tatin C correlated with GFR (1/cystatin C vs. GFR: r = 0.32; p = 0.0387), e specially in men (1/cystatin C vs. GFR: r = 0.64; p = 0.0055), but not to l ean tissue mass. These results might explain previous observations that ser um cystatin C seems to be a better marker for GFR than serum creatinine, pa rticularly for individuals with small to moderate decreases in GFR. However , the results also show that the serum concentrations of both creatinine an d cystatin C are determined not only by GFR, but also by other factors. Sin ce these additional factors differ for cystatin C and creatinine, it seems justified to use serum creatinine and cystatin C in conjunction to estimate GFR, at least until it is known in what situations serum creatinine or cys tatin C is the preferable marker.