Decision Threshold for Kryptor sFlt‐1/PlGF Ratio in Women With Suspected Preeclampsia: Retrospective Study in a Routine Clinical Setting

BACKGROUND: The objective was to evaluate predictive performance and optimal decision threshold of the Kryptor soluble fms‐like tyrosine kinase‐1 (sFlt‐1)/placental growth factor (PlGF) ratio when implemented for routine management of women presenting with symptoms of preeclampsia. METHODS AND RESULTS: Observational retrospective study of a cohort of 501 women with suspected preeclampsia after 20 weeks of gestation. Women referred to maternity ward for observation of preeclampsia had an sFlt‐1/PlGF ratio test included in routine diagnostic workup. Maternal and offspring characteristic data included maternal risk factors, outcomes, delivery mode, and indication for suspected preeclampsia. Biochemical measurements to determine sFlt‐1/PlGF ratio were performed using the BRAHMS/Kryptor sFlt‐1/PlGF ratio immunoassays. Results were analyzed by area under receiver‐operating characteristic curve. Preeclampsia occurred in 150 of 501 (30%) of symptomatic women with an sFlt‐1/PlGF ratio determined before the time of diagnosis. Area under receiver‐operating characteristic curve for diagnosis of early‐onset preeclampsia within 1 and 4 weeks was 0.98 (95% CI, 0.96–1.00) and 0.95 (95% CI, 0.92–0.98), respectively. For late‐onset preeclampsia, predictive performance within 1 and 4 weeks was lower: 0.90 (95% CI, 0.85–0.94) and 0.85 (95% CI, 0.80–0.90), respectively. The optimal single sFlt‐1/PlGF ratio threshold for all preeclampsia and late‐onset preeclampsia within 1 and 4 weeks was 66. The negative and positive predictive values for ruling out and ruling in developing preeclampsia within 1 week were 96% and 70%, respectively. CONCLUSIONS: The Kryptor sFlt‐1/PlGF ratio is a useful clinical tool ruling out and in preeclampsia within 1 week. Prediction within 4 weeks is superior for early‐onset preeclampsia. A single decision threshold of 66 is indicated for use in clinical routine.