Stepwise input
Practical use: Start with the assay framework rather than the number alone. The same ratio may mean different things depending on platform, gestational age, clinical setting, and whether the goal is rule-out, diagnostic support, or short-term severe-features risk.
Confirm framework fit
Selecting multiple gestation opens the twin-specific “why the test may be used” section and shows both singleton/framework and twin-evidence biomarker zones.
Enter biomarker result
Enter ratio directlyUse when lab reports the sFlt-1/PlGF ratio.
Calculate from sFlt-1 and PlGFUse values from the same assay report.
Add clinical concern markers
Clinical override: Biomarker reassurance should not override severe maternal findings, worsening laboratory values, or nonreassuring fetal status.
Generate interpretation
EMR text will be generated after interpretation.
Clinical use, limitations, and evidence
Low biomarker concernUseful for short-term reassurance only when assay and population fit. Continue clinical surveillance if symptoms, BP, labs, or fetal findings are concerning.
Intermediate zoneNot clearly reassuring and not clearly high-risk. Best used to justify closer follow-up, repeat assessment, and individualized retesting.
High biomarker concernSupports increased concern for evolving preeclampsia or placental dysfunction, but is not a stand-alone delivery trigger.
Implementation table: what the test can and cannot do
| Question | How to use the biomarker | Clinical limitation |
|---|---|---|
| Can it diagnose preeclampsia alone? | No. Use as adjunctive evidence. | Diagnosis still requires BP, symptoms, labs, and maternal/fetal assessment. |
| Can it rule out short-term disease? | Yes, in matched frameworks; Elecsys ratio <38 is best validated for 1-week rule-out. | Does not guarantee safety for 4 weeks and does not exclude later disease. |
| Can it predict severe progression? | Yes, assay-specific; U.S. BRAHMS KRYPTOR ratio ≥40 addresses 2-week severe-features progression risk. | Validated population matters. Twin and CKD data exist, but thresholds are less standardized and task-specific. |
| Can it guide surveillance? | Yes. It can support lower, intermediate, or higher action intensity. | Surveillance depends on clinical findings, fetal growth/Dopplers, and local protocol. |
| Can it determine delivery timing? | No. It should not be used alone for planned early birth. | NICE explicitly frames PlGF testing as adjunctive with standard assessment. |
NICE PlGF-based testing context
NICE supports selected PlGF-based tests with standard clinical assessment for suspected preterm preeclampsia from 20w0d to 36w6d. NICE guidance is best framed as diagnostic-support and triage support, not as permission to delay or mandate delivery. Planned early birth decisions should not be based on PlGF testing alone.
Repeat testing
Repeat testing may be clinically reasonable when symptoms evolve, blood pressure worsens, laboratory values trend adversely, fetal growth or Dopplers worsen, or the initial result is intermediate/equivocal. Routine serial intervals are not standardized across all guidelines and should follow local protocol.
Multiple gestation: why the test may be used
Do not describe use in twins as simple extrapolation. Twin pregnancies are not an automatic exclusion. The rationale is twin-specific: studies in twins show that the sFlt-1/PlGF ratio is associated with preeclampsia, PE-related adverse outcomes, indicated delivery for maternal PE complications, fetal growth restriction, placental dysfunction, and birthweight/neonatal outcomes.
Practical distinction: the biomarker appears clinically informative in twins, but the purpose of use should be stated clearly. Use it as adjunctive risk stratification, short-term reassurance/prognosis, or placental-dysfunction context—not as a stand-alone diagnostic test or automatic delivery trigger.
| Clinical question in twins | Twin-specific evidence | How to phrase use in the report |
|---|---|---|
| Does the ratio carry biologic and clinical signal in twins? | Reviews report that sFlt-1 and the sFlt-1/PlGF ratio tend to be higher in twins than singletons, especially later in gestation, and that the ratio is associated with PE, adverse pregnancy outcomes, and shorter time to delivery. | “Twin gestation selected. The ratio is biologically and clinically relevant in twins, but baseline distributions differ from singletons.” |
| Can the ratio help identify preeclampsia in twins? | A 2024 systematic review/meta-analysis of 7 studies including 442 twin pregnancies found pooled sensitivity 0.84, specificity 0.89, positive likelihood ratio 32.76, negative likelihood ratio 0.03, diagnostic odds ratio 35.72, and AUC 0.92 for PE prediction/identification. | “Twin-specific meta-analysis supports diagnostic association with preeclampsia; interpret with BP, symptoms, labs, growth, and Dopplers.” |
| Can a low ratio provide short-term reassurance? | Binder et al. reported that sFlt-1/PlGF <38 ruled out delivery because of PE within 1 and 2 weeks in twin pregnancies with NPV 98.8% and 96.4%, respectively. | “In selected twin pregnancies, a ratio <38 may support short-term reassurance regarding PE-related indicated delivery, but does not exclude later disease.” |
| Can a high ratio support closer surveillance? | Rana et al. found higher ratios in twins with PE-related adverse outcomes than without; the difference was more prominent before 34 weeks. Karge et al. reported shorter mean time until delivery when ratios were elevated. | “An elevated ratio supports increased concern for evolving placental disease and may justify intensified maternal/fetal surveillance.” |
| Can the ratio help with FGR/placental dysfunction risk in twins? | Martínez-Varea et al. reported that ratio ≥17 at 24 weeks was associated with later PE and FGR. Satorres-Pérez et al. found serial 12-, 24-, and 32-week ratios associated with placental dysfunction, birthweight percentile, neonatal admission days, and earlier delivery. | “Use as adjunctive placental-dysfunction context, especially when FGR, growth discordance, abnormal Dopplers, or hypertensive symptoms are present.” |
CKD / renal disease and superimposed preeclampsia
Do not frame CKD as making the biomarker invalid. CKD, chronic hypertension, diabetic kidney disease, lupus nephritis, and baseline proteinuria make the clinical diagnosis of superimposed preeclampsia more difficult. Angiogenic biomarkers can be useful adjuncts because preeclampsia is typically associated with lower PlGF, higher sFlt-1, and a higher sFlt-1/PlGF ratio than stable CKD alone.
Practical interpretation: a low ratio or reassuring PlGF can support lower short-term concern when the assay and population fit, but it should not override worsening hypertension, rising creatinine, thrombocytopenia, transaminitis, pulmonary edema, neurologic symptoms, fetal growth restriction, abnormal Dopplers, or nonreassuring fetal status. A high ratio supports concern for superimposed preeclampsia or placental dysfunction, but does not by itself determine delivery timing.
| Clinical setting | How to use sFlt-1/PlGF or PlGF | Documentation language |
|---|---|---|
| Stable CKD or chronic hypertension with baseline proteinuria | Use as an adjunct to distinguish placental angiogenic imbalance from baseline renal disease. | “Interpret with baseline BP, urine protein, creatinine trend, symptoms, labs, fetal growth, and Dopplers.” |
| Suspected superimposed preeclampsia | Low ratio / reassuring PlGF may reduce short-term concern; high ratio increases concern for placental disease or PE progression. | “Biomarker supports/does not support angiogenic pattern of PE, but diagnosis remains clinical.” |
| Diabetic kidney disease, lupus nephritis, transplant, or complex renal disease | Potentially useful, but evidence is less broad than general obstetric populations and may vary by phenotype. | “Use as adjunctive risk stratification; do not use as a stand-alone rule-in/rule-out test.” |
FGR / placental dysfunction context
Elevated ratios can support concern for placental insufficiency, early FGR, worsening uteroplacental dysfunction, and adverse placental phenotypes even before classic maternal criteria are fully expressed. However, use outside suspected preeclampsia populations is evolving and should be documented as adjunctive.
Clinical performance and references
| Framework | Primary use | Key threshold | Selected performance / note |
|---|---|---|---|
| Elecsys / PROGNOSIS | Short-term rule-out in suspected preeclampsia | Ratio <38 | High NPV for ruling out preeclampsia within 1 week; longer-term prediction is less precise. |
| Elecsys / expert consensus | Higher concern bands | >85 before 34w; >110 at/after 34w | Supports concern for preeclampsia/placental dysfunction when assay and clinical context match. |
| U.S. BRAHMS KRYPTOR / PRAECIS | 2-week severe-features progression risk | Ratio ≥40 | Reported sensitivity 94%, specificity 75%, PPV 65%, NPV 96% for progression to preeclampsia with severe features within 2 weeks. |
| NICE HTG630 | Diagnostic support/triage in suspected preterm PE | Assay-specific | Use with standard clinical assessment from 20w0d to 36w6d; not alone to decide planned early birth. |
| CKD / renal disease | Adjunctive assessment for suspected superimposed PE | Assay- and population-specific | Evidence supports improved discrimination/prediction in CKD cohorts, but results must be integrated with baseline proteinuria, creatinine trajectory, chronic hypertension, fetal growth, and Dopplers. |
| Twin pregnancies | Adjunctive PE/placental-dysfunction risk stratification and short-term prognosis | Use threshold according to clinical task: <38 has twin data for short-term PE-related delivery rule-out; other proposed twin cutoffs include 17 at 24w, 22.2 at 28–30w, 30.5 at 32w, and 53 in selected studies | Twin evidence supports clinical signal and prognostic use; avoid saying the value is merely extrapolated from singletons. |
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American College of Obstetricians and Gynecologists. Biomarker Prediction of Preeclampsia With Severe Features.Clinical Practice Update. June 2024. SMFM-endorsed.
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