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sFlt-1/PlGF Interpretation Guide

Clinical decision support for angiogenic biomarker interpretation in suspected preeclampsia and placental disease

sFlt-1/PlGF Biomarker interpretation for suspected preeclampsia

This caclulator separates the two most commonly encountered thresholds: the internationally used Elecsys/PROGNOSIS-style rule-out and rule-in framework, and the U.S. FDA-cleared 2-week severe-features risk framework. Those frameworks are platform-specific and should only be applied when they match the assay/report in use.

When this page is most useful

Use this in patients with suspected hypertensive disease or placental dysfunction when the clinical picture is uncertain and the lab has reported either a ratio directly or the raw sFlt-1 and PlGF values.

What this page does not do

This page does not diagnose preeclampsia by itself, does not determine delivery timing on its own, and does not assume that one manufacturer's thresholds can be transplanted to another assay without validation.

Quick interpretation panel

This remains interactive for bedside use, but the visual framing is intentionally closer to a reference page than to a conventional calculator.
Interpretation is best validated in singleton pregnancies. Twin data exist, but thresholds are less standardized.
Use the classic Elecsys/PROGNOSIS-style framework when the report matches that assay family and you want short-term rule-out and gestational-age-specific rule-in support.

Pre-interpretation cautions

Published package inserts and validation studies stress that these ratios are adjuncts. Assay mismatch or strong interference concern should push interpretation toward caution.

Biomarker entry

Enter ratio directly Use this when the report already gives the sFlt-1/PlGF ratio.
Enter sFlt-1 and PlGF The page will calculate the ratio for you.

Clinical features increasing concern

Language is deliberately conservative: the output describes how the biomarker shifts concern; it does not claim to replace diagnosis or management guidelines.

Interpretation summary

Awaiting inputs
Enter gestational age and biomarker information, then click Generate interpretation.

About the major thresholds

Classic Elecsys / PROGNOSIS family Ratio ≤38 is the widely cited short-term rule-out threshold in suspected preeclampsia; gestational-age-specific higher bands such as 85 before 34 weeks and 110 at 34 weeks or later support stronger concern when the report matches that assay.
U.S. 2-week severe-features framework Ratio 40 is tied to the U.S. FDA-cleared severe-features risk framework validated for progression to preeclampsia with severe features within 2 weeks in a defined hospitalized hypertensive pregnancy population.
Why one threshold does not fit all assays Published inter-assay work shows that raw values and ratio performance are not automatically interchangeable across platforms, so threshold borrowing should be avoided unless the assay has been clinically validated with that cutoff.

References

Core ratio interpretation studies
Zeisler H, Llurba E, Chantraine F, et al. The sFlt-1:PlGF Ratio in Women with Suspected Preeclampsia.
N Engl J Med. 2016;374(1):13-22. This pivotal prospective study established the widely used finding that a ratio of 38 or less had a very high negative predictive value for ruling out preeclampsia within 1 week, while a ratio above 38 increased the likelihood of disease within 4 weeks.
PMID: 26735990. PubMed
Zeisler H, Llurba E, Chantraine F, et al. Predictive value of the sFlt-1:PlGF ratio in women with suspected preeclampsia.
N Engl J Med. 2016;374(18):1785-1786. Brief correspondence highlighting the predictive framework and threshold interpretation derived from the PROGNOSIS dataset.
PMID: 27144854. PubMed
Zeisler H, Llurba E, Chantraine F, et al. Ruling out pre-eclampsia for up to 4 weeks and value of retesting with the Elecsys sFlt-1/PlGF ratio.
Ultrasound Obstet Gynecol. 2019;53(3):367-375. Extended follow-up analysis showing that the ratio can help rule out preeclampsia for longer intervals, with highest confidence over the short-term window.
PMID: 30014562. PubMed
Verlohren S, Brennecke SP, Galindo A, et al. Clinical interpretation and implementation of the sFlt-1/PlGF ratio in women with suspected preeclampsia.
Pregnancy Hypertens. 2022;27:42-50. Practical review summarizing use of the 38 rule-out cutoff, gestational-age-specific higher thresholds, and implementation issues in clinical care.
PMID: 34915395. PubMed
U.S. severe-features risk framework and contemporary data
Thadhani R, Lemoine E, Rana S, et al. Circulating Angiogenic Factor Levels in Hypertensive Disorders of Pregnancy.
NEJM Evidence. 2022. PRAECIS validated a ratio threshold of 40 for progression to preeclampsia with severe features within 2 weeks in a defined U.S. hospitalized hypertensive pregnancy population.
PMID: 38319832. PubMed
Burns LP, Potchileev S, Mueller A, et al. Real-world evidence for the utility of serum soluble fms-like tyrosine kinase-1/placental growth factor test in hypertensive disorders of pregnancy.
Am J Obstet Gynecol. 2025;232(2):129.e1-129.e13. Real-world U.S. implementation study supporting clinical utility of the ratio 40 framework for severe-features risk stratification within 2 weeks.
PMID: 39029547. PubMed
Miller JJ, Shriver EM, O'Donnell B, et al. Clinical Validation of the sFlt-1:PlGF Ratio as a Biomarker for Preeclampsia.
Reprod Sci. 2023;30(7):2040-2049. Useful contemporary U.S. clinical validation paper emphasizing that cutoffs and performance vary by the clinical question being asked.
PMID: 36869760. PubMed
Guidelines, reviews, and broader context
Brown MA, Magee LA, Kenny LC, et al. The hypertensive disorders of pregnancy: ISSHP classification, diagnosis and management recommendations for international practice.
Pregnancy Hypertens. 2018;13:291-310. Major international guideline document recognizing the role of angiogenic imbalance and biomarker adjuncts in preeclampsia evaluation.
PMID: 29803330. PubMed
Ukah UV, Hutcheon JA, Payne B, et al. Placental Growth Factor for the Prognosis of Women With Preeclampsia.
Hypertension. 2017;70(6):1228-1237. Prognostic review supporting angiogenic biomarkers as adjuncts for maternal and perinatal risk assessment.
PMID: 29084878. PubMed
Zhang L, Li W, Chi X, et al. Predictive performance of sFlt-1, PlGF and the sFlt-1/PlGF ratio for preeclampsia: a systematic review and meta-analysis.
J Gynecol Obstet Hum Reprod. 2025;54(4):102925. Recent meta-analysis reinforcing that the ratio generally outperforms either marker alone, while highlighting heterogeneity and platform differences.
PMID: 39947348. PubMed
NICE diagnostics guidance update on PLGF-based testing for suspected preterm pre-eclampsia.
Current NICE update continues to discuss use of PLGF-based testing, including the Elecsys sFlt-1/PlGF ratio, as an adjunct to standard clinical assessment rather than as a stand-alone test.
NICE diagnostics guidance update