Study suggests race adjustment unnecessary for alpha fetoprotein prenatal testing

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University of Washington (UW) School of Medicine researchers recommend discontinuation of a race-based adjustment to test-result values from a common prenatal screening.

The research, published last week in Obstetrics and Gynecology, questioned the decades-old practice of routinely adjusting alpha fetoprotein (AFP) values by approximately 10% for Black mothers.

AFP, a protein normally made by the baby’s liver, crosses the placenta into the mother’s blood serum. By the 1970s, maternal AFP measurements had become the go-to prenatal screening test for increased risk of Down syndrome, trisomy 18, or spina bifida. Other conditions, such as maternal weight, smoking status, diabetes, and chronic hypertension, were eventually also found to change AFP serum concentrations. At the time, race was also considered a mitigating factor; this has persisted in AFP test interpretation ever since.

A retrospective review of 27,710 medical records at UW Medicine hospitals evaluated AFP levels in pregnant patients between January 2007 and December 2020. Of these patients, 26,050 were non-Black and 1,660 were Black. All were lower-risk pregnancies with no diabetes, tobacco use, or multiple gestations. Linear regression models adjusted for gestational age and weight differences. The large data set enabled the researchers to confirm their hypothesis that there were no clinical measurable differences in maternal serum AFP between non-Black and Black patients.

Despite improvements in ultrasound technology and cell-free DNA testing at the forefront of more recent prenatal screening, AFP screening is still used to provide valuable information about pregnancy risks for patients with limited access to these newer tests. The historically-used adjustment for Black patients could potentially miss a case of spina bifida or incorrectly indicate Down syndrome. UW Medicine halted this practice about six months ago for prenatal screening tests, instructing its labs not to shift AFP values for Black mothers.

The researchers conclude that the continued inclusion of race to adjust serum AFP values, rather than obesity, tobacco use, diabetes, lack of folic acid, or other plausible biological risk factors, reflects the misrepresentation of race as a biological factor, rather than a social construct in medicine. They recommend that non-white expectant mothers ask their providers what tests they are prescribing and why, and whether their test results will be adjusted for race.

“We need an awareness that race-based corrections slink into medicine in many ways, and providers may not be aware they exist or that labs are making these corrections,” said UW senior author Dr. Shani Delaney in a statement. “While there are well established differences of medical outcomes by race, we can’t use race as a proxy for genetics or biology; instead we need to look at the underlying social determinants which lead to those outcomes.”

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