Preeclampsia affects only a small percentage of women, but the consequences of this inflammatory disorder are often life-threatening, Rina Shaikh-Lesko writes in the July Clinical Laboratory News.
Preeclampsia is not an easy condition to diagnose. Clinicians have typically relied on hypertension and new-onset proteinuria symptoms to guide a diagnosis, although the American College of Obstetricians and Gynecologists recently had to update its definition to reflect the complexity of the disorder. Pregnant women with symptoms that are either borderline or similar to other conditions, or who have pre-existing diseases that mask preeclampsia until it fully manifests, are particularly hard to diagnose.
Common diagnostic test results for preeclampsia include: thrombocytopenia, defined as a platelet count <100,000/µL; impaired liver function with enzymes “twice normal concentration”; and progressive renal insufficiency with serum creatinine concentration >1.1 mg/dL or in the absence of other renal disease, according to Shaikh-Lesko’s article. “Even with these diagnostic guideposts, clinicians would like better ways to identify preeclampsia earlier and to distinguish patients most at-risk of severe complications,” she writes. Many don’t have a full understanding of the condition’s pathogenesis. With this concern in mind, researchers have been searching for biomarkers that could help distinguish between women at risk for developing full-blown preeclampsia versus those whose condition is likely to stabilize.
The antiangiogenic factor soluble fms-like tyrosine kinase 1 (sFlt1) and the proangiogenic placental growth factor (PGF) or sFlt-1:PlGF ratio has shown promise in clinical research as a biomarker for predicting and diagnosing preeclampsia.
One international multicenter study in the New England Journal of Medicine determined that the sFlt1:PlGF ratio was effective in ruling out preeclampsia in more than 1,000 women suspected of having the condition.
The negative predictive value of this biomarker exceeded 99%. “If women with suspected preeclampsia had an sFlt-1:PlGF-ratio >38, the positive predictive value was 36.7 % for them to develop preeclampsia in the subsequent 4 weeks,” Shaikh-Lesko writes in summarizing the study results.
Not all experts are sold on this approach. Ann Gronowski, PhD, DABCC, FACB, professor of pathology and immunology and medical co-director of clinical chemistry at Washington University School of Medicine in St. Louis, believes sFlt1:PlGF’s negative predictive value is about as useful as a coin flip. This is because most women suspected of preeclampsia who undergo biomarker testing are going to test negative. This is true even among women with high blood pressure, Gronowski said.
“Gronowski is eager for a biomarker with a high positive predictive value that picks up the few patients who will go on to have preeclampsia from the many pregnant women with high blood pressure and proteinuria,” Shaikh-Lesko indicates. Gronowski offered that sFlt1:PlGF might be valuable for certain subpopulations of pregnant women—although those groups have yet to be identified.
Pick up the July issue of CLN and learn more about the pros and cons of using sFlt1:PlGF ratio to detect and diagnose preeclampsia.