Discrepancies between creatinine- and cystatin C-based equations: implications for identification of chronic kidney...

Early detection and treatment of chronic kidney disease (CKD) is important for slowing the progression of the disease and decreasing the associated risk of cardiovascular disease. This study examined how two creatinine-based and two cystatin C-based equations for calculating estimated glomerular filtration rate (eGFR) perform relative to each other in identifying CKD in a large cohort of community-dwelling individuals.

A total of 1630 adults were recruited from the Reykjavik area. Each subject's eGFR was calculated using the Modification of Diet in Renal Disease (MDRD) Study and Cockroft-Gault equations, and two cystatin C-based equations. The prevalence of decreased eGFR obtained by the four equations was compared and the relative performance of the equations examined.

The MDRD equation labelled significantly fewer individuals as having CKD (5.3%) relative to the other equations (12.8-19.7%). Agreement between equations was limited, with up to one-third of subjects diagnosed as having CKD by the MDRD equation being classified as normal by other equations. Correlations between creatinine- and cystatin C-based equations varied with age, gender and diuretic use.

The MDRD equation results in lower population-wide estimates of CKD relative to the other equations tested. An understanding of the performance of these equations is critical when they are used for estimating the prevalence of CKD in a population-wide setting or for diagnosing the disorder in clinical practice.