US FDA warns against false results from some prenatal blood tests

Washington: Blood tests that look for signs of genetic abnormalities in a foetus during pregnancy run the risk of producing false results and inappropriate use, warned the US Food and Drug Administration (FDA).

The agency warned against inappropriate use and wrong interpretation of results of non-invasive prenatal screening (NIPS) tests, also called cell-free DNA tests or non-invasive prenatal tests (NIPT).

It stated that although the tests are increasingly used, these have not been reviewed by the FDA. The claims about its performance and use are not based on sound science, the agency said.

“Without proper understanding of how these tests should be used, people may make inappropriate health care decisions regarding their pregnancy,” said Jeff Shuren, director of the FDA’s Center for Devices and Radiological Health, in a statement.

“We strongly urge patients to discuss the benefits and risks of these tests with a genetic counsellor or other health care provider prior to making decisions based on the results of these tests,” Shuren added.

NIPS tests can provide information about the possibility a child will be born with a serious health condition.

However, NIPS tests are screening tests – not diagnostic tests. They only provide information about the risk that a foetus may have a genetic abnormality, and additional testing may be needed to confirm whether or not a foetus is affected.

These genetic abnormalities can cause serious health conditions. Conditions caused by a missing chromosome or an extra copy of a chromosome are more common and may be easier to detect, such as Down syndrome, which can cause physical and intellectual challenges.

A missing or extra piece of a chromosome may result in rarer conditions, such as DiGeorge syndrome, which can cause heart defects, feeding difficulties, immune system problems and learning difficulties.

All NIPS tests on the market today are offered as laboratory developed tests (LDTs). Most LDTs, including NIPS tests, are offered without review by the FDA.

While many laboratories offering these tests advertise their tests as “reliable” and “highly accurate”, there are limitations due to the rarity of some of the conditions included in the screening, the FDA said.

For example, when screening for a very rare condition, a positive screening result may be more likely to be a false positive than a true positive, and the foetus may not actually be affected.

In other cases, a positive screening result may accurately detect a chromosomal abnormality, but that abnormality is present in the placenta and not in the foetus, which may be healthy, the agency explained.

The FDA warned that patients and health care providers should be aware of the risks and limitations of using these genetic prenatal screening tests and that they should not be used alone to diagnose chromosomal (genetic) abnormalities.