Assessment of Renal Function During Pregnancy Using a Random Urine Protein to Creatinine Ratio and Cockcroft-Gault Formula

The current standard for assessment of renal function in pregnant women is a 24-hour urine collection to determine creatinine clearance and proteinuria. It is easier to use the random urine protein to creatinine (P:C) ratio and the Cockcroft-Gault (CG) formula to estimate protein excretion and glomerular filtration rate, but the reliability of these formulae in combination for assessing renal function in pregnant women with renal disease is unknown. We compared the results of the P:C ratio with the 24-hour urinary protein excretion and the results of the CG clearance estimate with the 24-hour urine creatinine clearance in 34 pregnant women with underlying renal disease. Comparisons were made once in each trimester and postpartum. Prepregnancy weights were used in the CG formula: (140 - age × weight [kg] × 0.85)/72 × serum creatinine (mg/dL). Twenty-six first trimester, 33 second trimester, 21 third trimester, and 15 postpartum comparisons were made for creatinine clearance and 16 first trimester, 29 second trimester, 15 third trimester, and 15 postpartum comparisons were made for protein excretion. Measured creatinine clearance for the three trimesters combined (105 ± 40 mL/min [mean ± SD]) correlated significantly with CG clearances (113 ± 52 mL/min; r = 0.87). The mean P:C values (2.03 ± 3.15) for the three trimesters combined correlated significantly with 24-hour urine protein (2.25 ± 4.21 g; r = 0.92). Our study demonstrates excellent correlations between the CG formula using prepregnancy weights and 24-hour creatinine clearance and between the P:C and 24-hour urinary protein in this population. A urine P:C ratio ≤0.3 corresponded to a normal protein excretion with a positive predictive value of 80.1 and a negative predictive value of 93.9%. The P:C ratio and CG formula can be used in lieu of cumbersome 24-hour urine collections to assess protein excretion and creatinine clearance serially throughout pregnancy.