New tests for pre-eclampsia (PlGF-based testing)

This is a new guideline from NICE on using two new tests which will help in the diagnosis of pre-eclampsia. Although we are unlikely to be using these tests ourselves, we may start seeing patients who have had them used and so need to be aware of the implications. There is also a reminder that women at risk of pre-eclampsia (see the bottom paragraph) need 75mg of aspirin from 12/40, which we will need to prescribe and likely initiate.

These tests are the Triage PlGF test and the Elecsys immunoassay sFlt‑1/PlGF ratio. Two other tests have not been approved as they have not been shown to be accurate enough yet.

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When are these tests used?

These tests can be used between 20/40 and 34+6/40. A high result rules out pre-eclampsia. A low result does not currently rule in pre-eclampsia, however, it is possible that this will be an application of the test in the future. These tests can also not be used to diagnose or rule-out other placental disease, though again it is possible that they will be used for this in the future.

These tests are to be used with clinical judgement. For example a woman with high blood pressure and raised urinary protein may currently be very closely observed, or admitted. This test would allow a clearer idea of her risk of developing pre-eclampsia.

Are there problems with the test?

It is important to know that these tests are not 100% (though they are very good - they have a negative predictive value of 98-99%), so there will be the odd false negative. So if a woman has ongoing symptoms, she will need re-assessing.

...a previous negative test should not necessarily reassure you.

It is also worth knowing that it is unclear how long the test results are valid for, so if a woman starts getting symptoms again, she will need re-assessing - a previous negative test should not necessarily reassure you.

What do these tests measure?

So what on earth is this PlGF stuff? PlGF is placental growth factor. PlGF is involved in allowing the development of blood vessels in the placenta. A high level is reassuring. A low level suggests a problem.

Some PlGF-based tests measure soluble FMS‑like tyrosine kinase‑1 (sFlt‑1). This is thought to disable proteins, like PlGF, which are involved in placental blood vessel formation. sFlt-1 levels are higher in women who develop pre-eclampsia.

The guideline does have tables showing the cut-off values for a positive result, so you can refer to that if needed (it is complex, so I've not included it here).

Anything else we need to know?

There is nothing else new in this guideline, but there is a reminder of the risk-factors for pre-eclampsia and the need for women to take 75mg aspirin daily from 12 weeks, if they are at risk. We will need to prescribe this, so worth being aware of. Who needs aspirin? Women with 1 or more high-risk factor and 2 or more moderate risk factors:

High-risk factors

  • Hypertensive disease in a previous pregnancy
  • CKD
  • Autoimmune disease (eg SLE / antiphospholipid syndrome)
  • Type 1 or Type 2 DM
  • Chronic hypertension.

Moderate risk factors

  • First pregnancy
  • Aged 40 or over
  • Pregnancy interval of more than 10 years
  • BMI of 35 or more at first visit
  • Family history of pre-eclampsia
  • Multiple pregnancy

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