Onset threshold of the plasma levels of soluble fms-like tyrosine kinase 1/placental growth factor ratio for predicting the imminent onset of preeclampsia within 4 weeks after blood sampling at 19-31 weeks of gestation.

Our aim was to evaluate the onset threshold of plasma levels of the soluble fms-like tyrosine kinase 1 (sFlt-1)/placental growth factor (PlGF) ratio for predicting the imminent onset of preeclampsia (PE) within 4 weeks after blood sampling. We prospectively measured the plasma levels of sFlt-1 and PlGF by an automated electrochemiluminescence immunoassay at 19-25 weeks of gestation in 1199 women and at 26-31 weeks of gestation in 798 women. The onset threshold of the sFlt-1/PlGF ratio was determined as the 2.5th percentile of the 95th confidence interval (CI) of a regression line between the onset gestational weeks of PE and the standard deviation score of log10(sFlt-1/PlGF), using 25 samples taken within 1 week after the onset of PE. The imminent onset of PE was identified in 2 (0.2%) women recruited at 19-25 weeks and in 6 (0.8%) women recruited at 26-31 weeks. The onset threshold of plasma levels of the sFlt-1/PlGF ratio at 19-25 weeks showed a sensitivity (SE) of 1.00, a specificity (SP) of 1.00, a positive likelihood ratio (LR+) of ∞ and a positive predictive value (PPV) of 1.00; the onset threshold of plasma levels of the sFlt-1/PlGF ratio at 26-31 weeks showed a SE of 0.83, a SP of 0.994, a LR+ of 132 (95% CI: 51-339) and a PPV of 0.50. In conclusion, the onset threshold of plasma levels of the sFlt-1/PlGF ratio was shown to be a highly sensitive and a highly specific screening method for detecting the imminent onset of PE within 4 weeks after blood sampling at 19-31 weeks.