Correlation of Kryptor and Elecsys® immunoassay sFlt-1/PlGF ratio on early diagnosis of preeclampsia and fetal growth restriction: A case-control study.

Objectives: The measurement of the soluble fms-like tyrosine kinase-1 to placental growth factor (sFlt-1/PlGF) ratio on automated platforms has improved the detection of preeclampsia and fetal growth restriction (PE/FGR). The cut-off points of >38 and ≥85 has been defined for "rule in" and "aid in diagnosis", respectively, using the Elecsys® platform. We aimed to compare the performance of these cut-offs between the Elecsys® and Kryptor platforms at 24-28 weeks.

Study Design: Observational case-control study of singleton pregnancies at high risk for PE/FGR and sFlt-1/PlGF measurement at 24-28 weeks' gestation: 21 cases (9 early PE/FGR with delivery <32 weeks) were 1:1 matched for body mass index and parity with 21 controls. Correlations of the sFlt-1, PlGF and sFlt-1/PlGF values and diagnostic accuracy of the >38 and ≥85 cutoffs for early and late PE/FGR using Elecsys® and Kryptor assays were evaluated.

Main Outcome Measures: PE/FGR cases showed significantly higher median (IQR) sFlt-1/PlGF values at 24-28 weeks vs. controls, using both Elecsys® and Kryptor platforms: 55 (13-254) and 97 (13-530) vs. 4.1 (2.0-6.5) and 3.9 (1.8-7.7), respectively. The sFlt-1/PlGF correlation between both methods was excellent (r = 0.95) although lower PlGF and higher sFlt-1/PlGF values were observed with Kryptor. The higher diagnostic accuracy was obtained for early PE/FGR with the ≥85 cutoff (95.2%; 95%CI: 83.8-99.4%) in both platforms.

Conclusion: sFlt-1/PlGF measurements correlates well between Elecsys® and Kryptor platforms, and the cutoffs of >38 and ≥85 exhibit high diagnostic accuracy for assessing early PE/FGR at 24-28 weeks with both methods.