Assessment of renal function in geriatric palliative care patients - comparison of creatinine-based estimation equations

Background: Renal function impairment is common in geriatric palliative care patients. Accurate assessment of renal function is necessary for appropriate drug dosage. Several equations are used to estimate kidney function. Aims: 1) To investigate the differences (Delta) in kidney function assessed with simplified Modification of Diet in Renal Disease (MDRD), Berlin Initiative Study (BIS1), and Cockcroft-Gault (C-G) formulas in geriatric palliative care patients, and 2) to assess factors that may influence these differences. Methods: A retrospective analysis of data of patients aged >= 70 years admitted to a palliative care in-patient unit. The agreement between C-G, MDRD, and BIS1 equations was assessed with Bland-Altman analysis. Partial correlation analysis was used to analyze factors influencing the discordance. Results: A total of 174 patients ( 67 men; mean age 77.9 +/- 5.8 years) were enrolled. The mean Delta MDRD and C-G was 18.6 (95% limits of agreement 55.3 and-18.2). The mean Delta BIS1 and C-G was 6.1 (25.7 and -13.5), and the mean Delta MDRD and BIS1 was 12.5 (40.6 and -15.6). According to the National Kidney Foundation classification, 61 (35.1%) patients were differently staged using MDRD and C-G, while similar to 20% of patients were differently staged with BIS1 and C-G and MDRD and BIS1. Serum creatinine (SCr) and body mass index (BMI) had the most important influence on variability of Delta MDRD and C-G (partial R-2 37.7% and 28.4%). Variability of Delta BIS1 and C-G was mostly influenced by BMI (34.8%) and variability of Delta MDRD and BIS1 by SCr (42.2%). Age had relatively low influence on differences between equations (3.1%-9.5%). Conclusion: There is a considerable disagreement between renal function estimation formulas, especially MDRD and C-G in geriatric palliative care patients, which may lead to errors in drug dosage adjustment. The magnitude of discrepancy increases with lower SCr, lower BMI, and higher age.