Reference Range Determination for the sFlt-1/PlGF Ratio in a Diverse Cohort of Pregnant Women in the United States.

Background: The serum soluble fms-like tyrosine kinase-1 (sFlt-1) to placental growth factor (PlGF) ratio is an established tool for predicting preeclampsia in many countries but is not widely adopted in the United States. This study aimed to determine reference ranges for the Elecsys® sFlt-1/PlGF ratio and the sFlt-1 and PlGF immunoassays (Roche Diagnostics International Ltd) in a diverse US population of healthy pregnant women.

Methods: This was a prospective, noninterventional sample and data collection study performed between November 2022 and November 2023 at 9 collection sites and one measurement site in the United States. Evaluable women were ≥18 years old, apparently healthy, between 23 + 0 to 40 + 6 gestational weeks with a singleton pregnancy and had one serum sample collected. Reference ranges for 23 + 0 to 40 + 6 gestational weeks and 5 gestational windows within this range were determined using a nonparametric method.

Results: Of 818 recruited women, 561 were evaluable for the analysis and were representative of the US population in terms of self-reported race, ethnicity, and maternal age. Reference ranges for the sFlt-1/PlGF ratio, as determined by the 2.5th and 97.5th percentiles (90% CIs), were 0.9 (0.7, 1.0) to 13.5 (11.6, 14.9) for a US intended use population at 23 + 0 to 34 + 6 gestational weeks (n = 380) and 0.9 (0.7, 1.1) to 40.8 (29.0, 47.2) for the entire evaluable population at 23 + 0 to 40 + 6 gestational weeks.

Conclusions: Reference ranges were determined for sFlt-1/PlGF and the sFlt-1 and PlGF immunoassays in a diverse, healthy US population of pregnant women at 23 + 0 to 40 + 6 gestational weeks.