Creatinine- versus cystatin C-based renal function assessment in the Northern Manhattan Study

BACKGROUND: Accurate glomerular filtration rate estimation informs drug dosing and risk stratification. Body composition heterogeneity influences creatinine production and the precision of creatinine-based estimated glomerular filtration rate (eGFR(cr)) in the elderly. We compared chronic kidney disease (CKD) categorization using eGFR(cr) and cystatin C-based estimated GFR (eGFR(cys)) in an elderly, racially/ethnically diverse cohort to determine their concordance. METHODS: The Northern Manhattan Study (NOMAS) is a predominantly elderly, multi-ethnic cohort with a primary aim to study cardiovascular disease epidemiology. We included participants with concurrently measured creatinine and cystatin C. eGFR(cr) was calculated using the CKD-EPI 2009 equation. eGFR(cys) was calculated using the CKD-EPI 2012 equation. Logistic regression was used to estimate odds ratios and 95% confidence intervals of factors associated with reclassification from eGFR(cr)≥60ml/min/1.73m(2) to eGFR(cys)<60ml/min/1.73m(2). RESULTS: Participants (n = 2988, mean age 69±10yrs) were predominantly Hispanic, female, and overweight/obese. eGFR(cys) was lower than eGFR(cr) by mean 23mL/min/1.73m(2). 51% of participants’ CKD status was discordant, and only 28% maintained the same CKD stage by both measures. Most participants (78%) had eGFR(cr)≥60mL/min/1.73m(2); among these, 64% had eGFR(cys)<60mL/min/1.73m(2). Among participants with eGFR(cr)≥60mL/min/1.73m(2), eGFR(cys)-based reclassification was more likely in those with age >65 years, obesity, current smoking, white race, and female sex. CONCLUSIONS: In a large, multiethnic, elderly cohort, we found a highly discrepant prevalence of CKD with eGFR(cys) versus eGFR(cr). Determining the optimal method to estimate GFR in elderly populations needs urgent further study to improve risk stratification and drug dosing.