Clinical utility of the sFlt-1/PlGF ratio in obstetric triage
Measurement of the sFlt-1/PlGF ratio may help guide clinical care among patients referred to obstetric triage or admitted to the hospital for the evaluation of suspected preeclampsia. In one study, 402 patients with a singleton pregnancy referred to the hospital for evaluation of suspected preeclampsia, had a standard evaluation plus measurement of an sFlt-1/PlGF ratio.13 The clinicians caring for the patients did not have access to the sFlt-1/PlGF test results. In this cohort, 16% of the patients developed preeclampsia with severe features in the 2 weeks following the initial assessment in triage. In this cohort, a normal sFlt-1/PlGF ratio reliably predicted which patients were not going to develop preeclampsia with severe features over the following 2 weeks, with a negative predictive value of 98%. Among the patients with an elevated sFlt-1/PlGF ratio, however, the positive predictive value of the test was 47% for developing preeclampsia with severe features within the 2 weeks following initial evaluation. Among patients < 34 weeks’ gestation, an elevated sFlt-1/PlGF ratio had a positive predictive value of 65%, and a negative predictive value of 98%. Other studies also have reported that the sFlt-1/PlGF ratio is of value for assessing the risk for progression to preeclampsia with severe features in patients being evaluated for suspected preeclampsia.6,17,18
In obstetric triage, it is difficult to predict the clinical course of patients referred for the evaluation of suspected preeclampsia based on BP measurements or standard laboratory tests. The sFlt-1/PlGF test will help clinicians identify patients at low and high risk of progressing to preeclampsia with severe features.19 Patients with a normal sFlt-1/PlGF test are at low risk of developing preeclampsia with severe features over the following 2 weeks. Patients with an elevated sFlt-1/PlGF test are at higher risk of progressing to preeclampsia with severe features and may warrant more intensive obstetric care. An enhanced care program might include:
- patient education
- remote monitoring of BP or hospitalization
- more frequent assessment of fetal well-being and growth
- administration of glucocorticoids to advance fetal maturity, if indicated by the gestational age.
Twin pregnancy complicated by preeclampsia
Twin pregnancy is associated with a high risk of developing preeclampsia and fetal growth restriction. For patients with a twin pregnancy and a hypertensive disorder in pregnancy, an elevated sFlt-1/PlGF ratio is associated with the need for delivery within 2 weeks and an increased rate of adverse maternal and neonatal outcomes. In a retrospective study involving 164 patients with twin pregnancy first evaluated for suspected preeclampsia at a median gestational age of 33w4d, the sFlt-1/PlGF ratio was positively correlated with progression of preeclampsia without severe features to severe features within 2 weeks.20 In this cohort, at the initial evaluation for suspected preeclampsia, the sFlt-1/PlGF ratio was lower among patients who did not need delivery within 2 weeks compared with those who were delivered within 2 weeks, 24 versus 84 (P<.001). The mean sFlt-1/PlGF ratio was 99 among patients who needed delivery within 1 week following the initial evaluation for suspected preeclampsia. Among patients who delivered within 1 week of presentation, the reasons for delivery were the development of severe hypertension, severe dyspnea, placental abruption, rising levels of serum liver function enzymes, and/or onset of the HELLP syndrome.
An important finding in this study is that a normal sFlt-1/PlGF ratio predicted that the patient would not need delivery within 2 weeks, with a negative predictive value of 96%. Other studies also have reported that an elevated sFlt-1/PlGF ratio in twin pregnancies is associated with an increased risk of adverse outcomes and early delivery.21-23 An adequately powered multicenter study of twin pregnancies is needed to identify the sFlt-1/PlGF ratio associated with the greatest combined negative and positive predictive values.
The sFlt-1/PlGF test is a welcome addition to OB care
FDA approval of laboratory tests to measure circulating levels of sFlt-1 and PlGF will advance obstetric practice by identifying patients with a hypertensive disorder in pregnancy who are at low and high risk of developing preeclampsia with severe features within 2 weeks of the test. No laboratory test can replace the clinical judgment of obstetricians who are responsible for balancing the maternal and fetal risks that can occur in the management of a patient with a hypertensive disorder in pregnancy. The sFlt-1/PlGF ratio is highly dependable for identifying those patients with a hypertensive disorder in pregnancy who will not progress to severe disease within 2 weeks. The sFlt-1/PlGF ratio also identifies those patients with preeclampsia who are most likely to have adverse maternal and neonatal outcomes. The patients with an elevated sFlt-1/PlGF ratio may need more intensive antenatal care and consideration for transfer to a health system with a higher level of maternal and neonatal services. The sFlt-1/PlGF test is a welcome addition to obstetric care because it will improve the precision of our management of pregnant patients with hypertension. ●
rbarbieri @mdedge.com