Complement C5b-9 membrane attack complex as a marker of severe preeclampsia

Aim : to assess diagnostic value for quantitating plasma and urinary levels of the membrane attack complex C5b-9 measured to discriminate severe from moderate preeclampsia (PE), to establish cut-off values and to examine their association with markers of organ dysfunction and coagulopathy. Materials and Methods . A prospective, controlled, observational, comparative, non-randomized, cross-sectional study enrolled 80 pregnant women: 50 with PE (21 moderate and 29 severe; 24 early-onset and 26 late-onset) and 30 healthy pregnant controls. Plasma and urinary C5b-9 were measured by enzyme-linked immunosorbent assay on the day of diagnosis. Diagnostic accuracy was evaluated using receiver operating characteristic (ROC) curve analysis; optimal cut-offs were selected by the Youden index. Results . Median [lower; upper quartile] C5b-9 levels were higher in severe vs. moderate PE: 1934.9 [1510.2; 2262.3] pg/mL vs. 314.0 [120.1; 757.4] pg/mL in plasma and 555.0 [364.0; 830.0] pg/mL vs. 119.3 [40.4; 224.3] pg/mL in urine (both p < 0.001), regardless of onset time. The area under the ROC curve for this parameter was 0.974 and 0.864 for plasma and urine samples, respectively. A plasma cut-off of ≥ 1042 pg/mL provided 93.1 % sensitivity and 100.0 % specificity, and a urinary cut-off of ≥ 250 pg/mL provided 89.7 % sensitivity and 81.0 % specificity. All severe cases exceeded at least one cut-off threshold. Higher C5b-9 levels were associated with lower platelet count, fibrinogen concentration and birth weight, while urinary C5b-9 correlated positively with lactate dehydrogenase and aspartate aminotransferase activity. Conclusion . Plasma and urinary C5b-9 measured at diagnosis accurately identify severe preeclampsia and reflect the degree of coagulopathy and organ injury. The proposed thresholds require external validation in multicentre studies using the same assay.