OI-B-2Does the calculated creatinine clearance predict measured creatinine clearance in the pregnant woman?

AIMS Assessment of renal function in pregnancy currently requires a 24-hour urine creatinine clearance (CrCl). This study compared the Cockcroft & Gault estimation with the measured CrCl in pregnant women. The 24-hour CrCl was also compared to shorter collection intervals. METHODS This is a prospective, cohort study of pregnant women admitted to the antepartum service at Northwestern Memorial Hospital. Urine was collected in 3 sequential intervals: 2, 6 and 16 hours. Data included: height, weight, age, ethnicity, obstetrical and medical history and serum creatinine. A 24-hour measured CrCl was calculated from the pooled collections and using Pearson's correlation compared to the Cockcroft & Gault estimation using ideal body weight and actual body weight. Using ANOVA, the 24-hour CrCl was also compared to the clearances in the shorter collections. RESULTS Of the 71 women enrolled, 63 completed the study. The calculated CrCl using actual body weight was a better approximation for measured CrCl than ideal body weight (r = .738 and .591, respectively, P=0.01). Substituting a correction factor of .8 rather than .85 in the formula with actual body weight improved the percentage of women with estimated clearances within 20% of measured (70.4% vs 46%). The 2-hour collection significantly overestimated CrCl compared to the other collection intervals (P=0.001). CONCLUSIONS The Cockcroft & Gault calculation using actual body weight and a correction factor of .8 reliably estimates CrCl in the pregnant patient. Clinical Pharmacology & Therapeutics (2005) 79, P2–P2; doi: 10.1016/j.clpt.2005.12.007