NEWS

"New" Screening Test

 CNN published a news article today about a “new” preeclampsia screening test available in the US. It is often the case that health articles written by journalists who are not in the research field do a poor job of explaining the research. Hopefully we can help clear up some misconceptions and misinformation.

First, this is not a new test. It is a combination of four already-existing tests that have been widely available in the US for years. Each test individually can give us some information about risk, but by using them together, it increases the accuracy as a screening tool. The test combination is already in use in some countries, and even some doctors in the US have been using it. The only thing new is that it is being offered by a major nation-wide testing company for the first time.
 

This combination of tests can be done in the first trimester, usually between 11 and 14 weeks. The results can help screen patients who are at higher risk for developing early-onset preeclampsia before 34 weeks. The screening boasts a 90% sensitivity and 90% specificity. In my opinion, and in the opinion of many experts, this is not nearly as high as we would like it to be.

Specificity refers to how many people are screened as high risk yet end up being fine, what a layperson might call a “false positive”. (It is not really a positive/negative test, but it may help you understand the concerns.) The false positives we can live with—if someone screens high risk and ends up fine, they may have more appointments and some extra worry, but no real harm done.

The bigger concern is the sensitivity, the rate of “false negatives”. Think about it—10% of cases who will develop preeclampsia before 34 weeks are told they are low risk and then end up getting it anyway. It is very important for both doctors and patients to understand that these are rule-in tests, not rule-out tests. If you test high risk, you are ruled into closer monitoring. But if you test low risk, preeclampsia has not been ruled out. You should still take symptoms seriously in case you are part of that 10% who end up getting early-onset preeclampsia anyway.

Which brings me to my next point: the 90% sensitivity is only for early-onset cases. It is less helpful at predicting late-preterm cases (34-37 weeks), even worse at term cases (37+ weeks) and completely useless at predicting postpartum cases. Since the vast majority of cases develop at term or late-preterm, this test will miss a lot of cases. Many patients who will get preeclampsia will be told they are low-risk only to get it anyway. Could this lead to bad outcomes if they ignore symptoms, wrongly thinking they are safe?

ACOG (US pregnancy guidelines) released this statement: “It is currently unclear how useful the LabCorp test will be in accurately predicting risk for developing preeclampsia and whether it is appropriate for all pregnant patients. Before a screening test can be successfully employed, there needs to be an evidence-based intervention to either prevent or reduce the impact of the disease. We currently have no data on how to reduce the risk for a pregnant patient predicted to have preeclampsia from a blood test early in pregnancy as opposed to clinical factors.”

In other words, knowing you are at high risk may not change anything in the outcome. Doctors and patients can still only wait and watch until symptoms appear. There is no treatment for preeclampsia except delivery. The article incorrectly states that “severe cases can be treated with medication,” but those medications only treat the symptoms, not preeclampsia itself. Patients with severe symptoms still need to deliver even while being treated with medication.

This brings me to the worst part of the article. LabCorp’s chief medical and scientific officer claims, “At least half or more cases of preeclampsia are potentially preventable.” I am sorry, but I will need to see what research he is basing this on. The only thing proven to lower the risk of preeclampsia is low dose aspirin. The studies so far have mostly been about preventing recurrence, not first-time cases. It seems to work in somewhere between 5-15% of cases, not 50% or more!

The article also suggests that patients can be seen more often and check their blood pressure at home. This will not prevent preeclampsia, only help identify it after it develops. And it suggests “not overexerting yourself during exercise or at work.” Again, I need to see the research. My role here at EndPreeclampsia is to read research related to preeclampsia. I have seen hundreds of studies and am in contact with researchers around the world. I have yet to see anything that suggests taking it easy could prevent half or more of cases. In fact, it does not prevent preeclampsia at all!

The key for how useful this test will be is in the implementation. If doctors only test patients who they already know are high-risk based on other factors, it is not helpful. They can rule those patients into closer monitoring based on those other factors without bothering to test. It would need to become a standard screening for all patients, even those who otherwise appear to be low-risk. And both doctors and patients need to know that preeclampsia has not been ruled out. They cannot get complacent about identifying and evaluating symptoms.

What does this mean for you? If you are here to learn about preeclampsia, there is a good chance you have already been identified as high risk and have already been ruled into closer monitoring. You do not need a test to tell you that. But it is always worth a discussion with your doctor. You can ask whether they recommend it for you and why or why not. You can also ask how the results would affect your care. If you screen high risk, would you have more frequent appointments and tests? If the results show low risk, will that change your appointment schedule?

You can read CNN’s article in our support group: www.facebook.com/groups/preeclampsia

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