Grubb A et al. (2005) Simple cystatin-C-based prediction equations for glomerular filtration rate compared with the modification of diet in renal disease prediction equation for adults and the Schwartz and the Counahan–Barratt prediction equations for children. Clin Chem 51: 1420–1431

Serum creatinine level is generally used as a surrogate marker for glomerular filtration rate (GFR), but is affected by patient-specific factors including diet, sex, ethnicity and age. Complex prediction equations are necessary to correct for these factors. A Swedish group has found that GFR can be estimated solely from the concentration of cystatin C in plasma.

Data were analyzed from 536 consecutive patients (age 0.3–93 years; 274 males), for whom GFR had already been measured accurately using an invasive technique. Prediction equations for GFR were constructed on the basis of plasma cystatin C levels, and results were compared with those from the simplified 4-parameter Modification of Diet in Renal Disease equation (for adults) and the Schwartz and Counahan–Barratt equations (for children). The cystatin-C-based prediction equation developed using data from the adult cohort estimated GFR in adults at least as accurately as with current prediction equations, and performed equally well at predicting GFR in children aged >14 years. In children aged <14 years, the equation required a consistent adjustment factor.

Prediction equations are highly population-dependent, and the fact that this single-center study population included healthy individuals and did not include any African Americans or children aged <0.3 years might have affected the results; however, the study provides good support for the use of plasma cystatin C as a marker for GFR.