Comparison of Creatinine and Cystatin C to Estimate Renal Function in Geriatric and Frail Patients

The aim of this study was to compare estimated glomerular filtration rate (eGFR) with creatinine (eGFR(crea)) and cystatin C (eGFR(cys)) in geriatric and frail patients. A retrospective, cross-sectional study was performed at a geriatric clinic in Stockholm (n = 95). The revised Lund–Malmö equation was used to calculate eGFR(crea) and the Caucasian-Asian-Pediatric-Adult (CAPA) equation was used for eGFR(cys). The absolute mean percentage difference between eGFR(crea) and eGFR(cys) was used as a surrogate measure for accuracy in eGFR. Other outcome measures were consistency expressed in Lin’s concordance correlation coefficient and the proportion of consistent staging of renal failure. Subgroup analyses were performed with regard to frailty (according to Clinical Frailty Scale) and age. eGFR(cys) estimated lower GFR than eGFR(crea) across the entire study population as well as in all subgroups (p < 0.05). Difference between the estimates increased with increasing frailty (r(2) = 0.15, p < 0.01), but was not significantly affected by age (r(2) = 0.004, p = 0.55). In conclusion, eGFR(cys) was significantly lower compared to eGFR(crea) in geriatric and frail patients. Moreover, frailty had greater impact than age on the accuracy of eGFR. However, this study cannot determine if any of the estimates are preferable over the other in this patient group.