Discrepancies between creatinine‐based and cystatin C‐based equations in estimating prevalence of stage 3 chronic kidney disease in an elderly population

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Abstract
Background. The prevalence of stage 3 chronic kidney disease (CKD) is increasing, calculated using the modification of diet in renal disease (MDRD) study equation for estimating glomerular filtration rate (GFR). Cystatin C‐based equations are also being used to estimate GFR. Using creatinine‐based and cystatin C‐based equations, the aim of our study was to measure the difference in prevalence of stage 3 CKD in a population. Methods. CKD screening is organized in the Province of Liège, Belgium. On a voluntary basis, people aged between 45 and 75 years are invited for screening. GFR is estimated using the MDRD study equation and by the three recent cystatin C‐based equations proposed by Levey's group. The Levey 1 equation is based on cystatin C only and the Levey 2 equation on cystatin C corrected for age and sex. The Levey 3 equation combines cystatin C, creatinine, age and sex. Results. The population screened comprised 754 people. Cystatin C is highly correlated with creatinine (r = 0.6196, pConclusions. The prevalence of stage 3 CKD varies strongly following the method used for estimating GFR, creatinine‐based or cystatin C‐based equations. Such discrepancies must be confirmed and explained in additional studies using GFR measured with a reference method.