Renal function in older hospital patients is more accurately estimated using the Cockcroft-Gault formula than the modification diet in renal disease formula.

OBJECTIVES

To compare the accuracy of the two most popular creatinine clearance (CrCl) estimation formulae (Cockcroft-Gault (CG) and Modification Diet in Renal Disease (MDRD)) in older hospitalized patients.

DESIGN

Prospective, cross-sectional, observational study.

SETTING

Two hospital geriatric wards.

PARTICIPANTS

Consecutive patients aged 70 and older with an indwelling urinary catheter for the purpose of care.

MEASUREMENTS

CrCl was determined according to three methods: measured CrCl from plasma and urine creatinine and 24-hour urine volume, CG (CG-CrCl), and MDRD (MDRD-CrCl). Results were expressed as median and interquartile range (IQR). Moderate and severe renal impairment were defined as a CrCl between 30.0 and 59.9 mL/min and less than 30.0 mL/min, respectively.

RESULTS

One hundred twenty-one patients were included (46% male). Mean age was 86.1+/-6.7 (range 72-100). Median measured CrCl was 43.8 mL/min (IQR 33.6-61.1 mL/min), CG-CrCl was 40.9 mL/min (IQR 31.0-52.6 mL/min), and MDRD-CrCl was 61.3 mL/min (IQR 49.4-77.0 mL/min). The biases of CG-CrCl and MDRD were -3.5+/-22.5 and 20.1+/-28.2, respectively (P<.001). Misclassification of renal impairment (absent/moderate/severe) occurred in 33% of patients according to CG-CrCl, and concordance was mild to moderate (kappa=0.50). Misclassification occurred in 50% of patients according to MDRD-CrCl, and concordance was poor (kappa=0.33). Bias was significantly related to bed confinement for both formulae and to plasma creatinine for MDRD.

CONCLUSION

In elderly hospitalized patients, CG slightly underestimates CrCl, and MDRD strongly overestimates it. CG gave a better prediction of measured CrCl than MDRD.