In a poster presentation at the annual American College of Obstetricians and Gynecologists meeting in 2014, Rodrigue et al concluded that a protein-to-creatinine ratio of greater than or equal to 0.24 optimizes sensitivity and specificity. An optimal cutoff to diagnose preeclampsia helps in the appropriate and timely treatment of affected individuals. There has been little research on how race and body mass index (BMI, calculated as weight (kg)/[height (m)]2
) affect laboratory values for preeclampsia. Our objective was to determine whether there is a correlation between race and BMI on the overall cutoff for the optimal protein-to-creatinine ratio for the diagnosis of preeclampsia.
Using the previously collected data from Rodrigue et al, we retrospectively identified pregnant patients evaluated for preeclampsia who had both 24-hour timed urine collection and protein-to-creatinine ratio collected within 30 hours. Using 300 mg urine protein as diagnostic for preeclampsia, protein-to-creatinine ratios were analyzed by testing individual cutoff points. A receiver operating characteristic curve was constructed to determine maximum sensitivity and specificity and the area under the curve (AUC). We determined the optimal cutoff point for African Americans and Caucasians as well as for patients who are obese (BMI greater than 30) and nonobese (BMI less than 30).
One hundred eighty-eight patients were analyzed. One hundred five were African American (55.85%), for whom a maximum sensitivity (79.41%) and specificity (69.23%) were found at a protein-to-creatinine ratio cutoff point of 0.20; the AUC is 0.88 (95% confidence interval [CI] 0.81–0.95). Seventy-three patients were Caucasian (38.8%) and maximum sensitivity (84.00%) and specificity (84.78%) were found at a protein-to-creatinine ratio cutoff point of 0.27; the AUC is 0.88 (95% CI 0.79–0.98). One hundred seven obese patients were analyzed; maximum sensitivity (78.38%) and specificity (75.86%) were found at a protein-to-creatinine ratio cutoff point of 0.21; the AUC is 0.88 (95% CI 0.81–0.95). Eighty-one patients were nonobese; maximum sensitivity (83.33%) and specificity (84.21%) were found at a protein-to-creatinine ratio cutoff point of 0.25; the AUC is 0.89 (95% CI 0.80–0.98).
The results of this analysis show that the application of a “blanket cutoff” protein-to-creatinine ratio for every pregnant patient with suspected preeclampsia should be reevaluated. It seems that the optimal cutoff should be individualized by at least race, if not also BMI. Further research should be performed to better specify optimal cutoff for race and BMI.