In pregnant women with suspected preeclampsia, a soluble fms-like tyrosine kinase 1 (sFlt-1) to placental growth factor (PlGF) ratio of ≤38 can predict the absence of preeclampsia onset within 1 week of the blood test with over 90% accuracy, according to a study published in the New England Journal of Medicine.

Although low sFlt-1:PlGF ratios predicted the absence of preeclampsia, higher ratios of sFlt-1:PlGF did not consistently predict the onset of preeclampsia within 4 weeks of the blood test, according to Harald Zeisler, MD, and colleagues.

Before the clinical onset of preeclampsia, pregnant women have an elevated sFlt-1:PlGF ratio. However, it was unclear whether an elevated sFlt-1:PlGF ratio could predict the onset of preeclampsia.

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The researchers conducted an observational study that included women between the 24th and 37th week of a single-child pregnancy who had suspected preeclampsia. The investigators used blood tests to measure each woman’s sFlt-1:PlGF ratio to see if it could predict the absence of preeclampsia within 1 week and the presence of preeclampsia within 4 weeks.

In a developmental cohort of 500 women, the researchers determined that an sFlt-1:PlGF ratio cutoff of 38 had predictive value.

To validate this cutoff ratio, the researchers did blood tests for a subsequent validation cohort of 550 additional women. An sFlt-1:PlGF ratio of ≤38 had a 99.3% predictive rate for the absence of preeclampsia within 1 week of the blood test, with 80.0% sensitivity and 78.3% specificity. However, a ratio above 38 had a 36.7% predictive rate for a diagnosis of preeclampsia within 4 weeks of the blood test with 66.2% sensitivity and 83.1% specificity.


  1. Zeisler H, Llurba E, Chantraine F, et al. Predictive Value of the sFlt-1:PlGF Ratio in Women with Suspected Preeclampsia. N Engl J Med. 2016; 374:13-22.