Comparison of two test systems for sFlt-1 and PlGF – diagnostic accuracy for preeclampsia

Objective: The angiogenic factors sFlt-1, PlGF and the sFlt-1/PlGF-ratio have shown utility as a diagnostic test for preeclampsia (PE). Previous case control studies have determined cut-off values for sFlt-1 and PlGF with the Elecsys® assay (Roche Diagnostics). The objective of this study was to characterize angiogenic factor levels of sFlt-1, PlGF and sFlt-1/PlGF-ratio measured with the Kryptor® immunoassay (ThermoFisher Scientific) in normal and preeclamptic singleton pregnancies. Methods: In a cohort of n = 208 women, sFlt-1 and PlGF was measured with Kryptor® and ELECSYS® immunoassays. In the longitudinal arm of the study, sFlt-1 and PlGF were determined in n = 262 samples of n = 180 patients with an uneventful pregnancy outcome to generate normal ranges. A gestational-age matched comparison between n = 28 cases with preeclampsia (PE) and n = 108 controls in the third trimester was performed and a ROC analysis was executed to test and compare the diagnostic accuracy. Results: In patients with PE, sFlt-1 and the sFlt-1/PlGF ratio were significantly increased and PlGF was significantly decreased as compared to healthy controls (median (IQR) sFlt-1: 7664 pg/ml (6652 pg/ml) vs. 2365 pg/ml (2505 pg/ml), p < 0.001; sFlt-1/PlGF: 235.4 (381.7) vs. 13.78 (37.22), p < 0.001; PlGF: 36.86 pg/ml (26.72 pg/ml) vs. 160.40 pg/ml (258.5 pg/ml), p < 0.001). With an area under the curve of 0.930 when diagnosing PE, ROC analysis yielded an optimal cut-off at 103 with a sensitivity of 89.3% and a specificity of 90.7% when analysing the sFlt-1/PlGF ratio. The established cut-off values for Elecsys® at 38 and 85 when analysing the sFlt-1/PlGF ratio with the Kryptor® assay, result in a sensitivity of 92.9% and 89.3% and in a specificity of 72.2% and 87%. Conclusion: Performing the sFlt-1/PlGF ratio with the immunoassay Kryptor® by Thermo Scientific diagnoses PE with a diagnostic accuracy comparable to the cut-off values established with Elecsys® assays.