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Reproductive Endocrinology

MON-127 - Kryptor sFlt-1/PlGF Ratio Assays for Pre-Eclampsia Diagnosis: Refining Performance Using Real-World Data

Monday, June 15, 2026
9:00 AM - 2:00 PM CT
Disclosure(s):
Hannah Hooker, MSc: No financial relationships to disclose


Background: Pre-eclampsia is a hypertensive pregnancy disorder and a leading cause of maternal and perinatal morbidity and mortality. Placental dysfunction leads to an imbalance in circulating angiogenic factors, notably increased soluble fms-like tyrosine kinase-1 (sFlt-1) and reduced placental growth factor (PlGF). The sFlt-1/PlGF ratio is an established biomarker for prediction and diagnosis, with distinct rule-in and rule-out thresholds. However, real-world analytical comparability between assay platforms and transferability of clinical thresholds remain uncertain. This study compared the analytical and clinical performance of the Thermo Fisher Scientific™ B·R·A·H·M·S™ KRYPTOR™ sFlt-1 and PlGF assays with the NICE-approved Roche-Elecsys® assay and evaluated a single rule-in/out threshold compared to dual-threshold strategies for risk stratification.

Methods: sFlt-1 and PlGF were measured in two retrospective cohorts of 343 (Coventry) and 446 (Oxford) serum samples from women undergoing investigation for suspected pre-eclampsia. Samples were analysed using Thermo Scientific™ B·R·A·H·M·S™ KRYPTOR™ and Roche Elecsys® immunoassays. Method comparison was performed using Passing–Bablok regression and Bland–Altman analysis. Clinical performance of the sFlt-1/PlGF ratio was assessed against pregnancy outcomes (n = 303) across a range of thresholds. To examine the relationship between detection accuracy and pre-eclampsia risk, we applied equal-frequency binning to evaluate disease risk across sFlt1/PlGF ratio groups. Classification performance was then compared using decision tree regression and Youden’s index, which combines sensitivity and specificity into a single measure.

Results: Strong correlation (r > 0.98) was observed between platforms, but a positive bias in sFlt-1/PlGF ratios was identified with KRYPTOR™ compared to Elecsys® assays. Established Elecsys-derived cut-offs (33 and 85) were not directly transferable to the KRYPTOR™ platform, resulting in an 8-9% misclassification rate. Equivalent thresholds of 48 and 110 were derived and compared with a single rule-in/out threshold of 66, which showed a higher Youden index, indicating improved sensitivity/specificity trade-off. Risk increased progressively across the intermediate (‘moderate risk’) range.

Conclusions: The B·R·A·H·M·S™ KRYPTOR™ sFlt-1 and PlGF assays demonstrate comparable diagnostic performance to the NICE-approved Roche Elecsys® assays, supporting their use in pre-eclampsia triage. However, assay-specific threshold adjustment is required to account for systematic differences and ensure consistent interpretation. While dual threshold strategies optimise rule-in and rule-out performance, a single-threshold approach may simplify clinical decision-making by removing the moderate-risk category while maintaining comparable classification performance.

*Unless otherwise noted, all abstracts presented at ENDO must not be released to the press or the public until the date and time of presentation. For oral presentations, the abstracts are embargoed until the session begins. The Endocrine Society reserves the right to lift the embargo on specific abstracts that are selected for promotion prior to or during ENDO.*