NICE recommends blood tests to help rule out suspected pre-eclampsia

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24 May 2016

Pre-eclampsia is the development of increased blood pressure and protein in the urine during pregnancy, usually during the second and third trimester. Symptoms other than those due to mild fluid retention, are often absent. There is poor development of the placenta, the growth of the baby is slowed and delivery may be premature. Those affected need to be monitored closely. About one in 50 will develop full eclampsia in the last three months of pregnancy or during labour. Eclampsia brings fits, fluid in the lungs, kidney failure and clotting problems and is a life-threatening condition for both mother and child. If a healthcare professional thinks a woman may have pre-eclampsia she is likely to be admitted to hospital for observation.

Research evidence supports the idea that pre-eclampsia follows a poor blood supply to the placenta causing release of molecules into the mother's circulation that affect her blood vessels. Four new commercial tests designed to help diagnose the condition are based on measurement of plasma placental growth factor (PlGF), a hormone that helps the growth of new blood vessels in the placenta. Normally PlGF concentrations increase during pregnancy; in pre-eclampsia they can be very low. Two of the four tests express PlGF as a ratio to the soluble fms-like tyrosine kinase (sFlt-1) concentration. This enzyme causes constriction of blood vessels; plasma concentrations are raised in pre-eclampsia.

The National Institute for Health and Care Excellence (NICE) assessed 12 publications of 4 studies and one multicentre study (as yet unpublished) about these four tests to help the NHS decide whether to use them. The review by NICE, published online on 11 May 2016, concluded that although all four tests show promise (with other tests and follow-up tests) for the diagnosis of pre-eclampsia, there was not enough evidence to recommend them at present.

However, between weeks 20 and 35 of pregnancy, two of the tests showed high accuracy in ruling out pre-eclampsia in the short term. The Triage PlGF test (Alere International) ruled out pre-eclampsia needing delivery within 14 days with 98% accuracy; the Elecsys immunoassay sFlt 1/PlGF ratio (Roche Diagnostics) ruled out pre-eclampsia for seven days with 99% accuracy. NICE concluded that during weeks 20 to 35 of pregnancy a negative result from either test could help decide whether the anxiety, inconvenience and expense of hospital admission was necessary, and if monitoring could continue in the community.