Diagnostic accuracy of cervicovaginal interleukin-6 and interleukin-6:albumin ratio as markers of preterm delivery.

BACKGROUND Absence of fetal fibronectin (fFN) in the cervicovaginal fluid (CVF) of women with symptoms of preterm labor is an excellent predictor of women who will not deliver within 2 weeks of testing. Preliminary studies suggest interleukin (IL)-6 performs similarly to fFN. The positive predictive values of both these assays are poor. Inconsistent specimen collection may explain this poor performance. The objective of this study was to validate the clinical utility of cervicovaginal IL-6 and investigate the utility of the IL-6:albumin ratio to predict delivery within 14 days. METHODS We quantified albumin and IL-6 with the DPC Immulite in 660 CVF specimens collected for physician-ordered fFN analysis. The clinical utility of IL-6 and IL-6:albumin to predict delivery within 14 days of collection was determined. RESULTS The sensitivity, specificity, and positive and negative likelihood ratios for delivery within 14 days were 65%, 87%, 4.8, and 0.4, respectively, for fFN and 35%, 91%, 3.8, and 0.7 for IL-6, with a 250 ng/L cutoff. With a preterm delivery prevalence of 4.7%, positive and negative predictive values were 19% and 98%, respectively, for fFN and 16% and 97% for IL-6. The areas under the ROC curves were 0.71 and 0.51 for IL-6 and IL-6:albumin, respectively. Odds ratios for delivery within 14 days of collection were 11.8 (P <0.0001), 5.5 (P = 0.0001), and 2.4 (P = 0.06) for fFN, IL-6, and IL-6:albumin, respectively. CONCLUSIONS Cervicovaginal IL-6 may have utility for predicting preterm labor while offering the potential for substantial cost savings. Assay performance characteristics are not improved by normalizing IL-6 to albumin.