Correlation of Measured and Estimated Creatinine Clearance in Hospitalized Elderly Patients: A Retrospective Cohort Study

Abstract

Background: Accurate assessment of renal function is essential in hospitalized elderly patients. Few studies have examined the accuracy of Cockcroft-Gault (C-G) estimates of creatinine clearance (CrCl) compared with measured clearance in these patients. Objective: The objective of this study was to determine the correlation between C-G estimates of CrCl and measured CrCl in hospitalized elderly patients. Methods: This Institutional Review Board–approved, single-center retrospective observational cohort study included all patients who were 65 years and older admitted to our medical center in January to September 2018 with either an 8- or 24-hour urine collected during admission. The primary outcome was correlation, bias, and precision of C-G estimates of CrCl versus measured CrCl using Pearson correlation, Spearman linear regression, and Bland-Altman analysis. Outliers were determined using a cut-off of ±20%. Data are presented as median (interquartile range) or percentages. Results: A total of 108 urine collections from 90 unique patients were included in the study. The patients were 51% female, median age was 71 (68-77) years, and median body mass index was 26.6 (22.8-31) kg/m2. Most collections were over 24 hours (66.7%), and 38% were performed while patients were in an intensive care unit. Median blood urea nitrogen (BUN) was 24.5 (17-36) mg/dL and median serum creatinine was 0.71 (0.55-1.09) mg/dL. The median C-G estimation was 75.4 (48.2-110.6) mL/min, and the median measured CrCl was 79.1 (38.1-99.5) mL/min, r2 = .56 ( P < .001). Bland-Altman analysis showed large limits of agreement (-75.5-57.7 mL/min), with a bias of −8.9 and precision (standard deviation of bias) of 34 mL/min. Outliers were common, with 38% of C-G estimation values >120% of measured CrCl, and 18% of C-G estimates <80% of measured CrCl. Conclusions: Measured CrCl varied significantly from C-G estimates in hospitalized elderly patients. It is important to recognize characteristics of patients who may benefit from measurement of CrCl. Future studies should examine the impact of this variance on clinical outcomes.