A test used to diagnose Type II diabetes and monitor blood sugar levels could be leaving hundreds of thousands of diabetic African Americans in the U.S. undiagnosed, according to a study published today in PLOS Medicine.

The test uses 60 genetic variants, according to a team of scientists, and one of those genetic variants is found only in African Americans. This particular genetic variant significantly reduces the accuracy of the blood test in question, the study reported.

The researchers suggested that healthcare workers screen for the particular genetic variant alongside the diabetes diagnostic test or simply use a different test in patient populations with African ancestry.

The study is the largest of its kind, the team touted, comprised of more than 200 scientists. The researchers were charged with investigating the genetic variants linked to a blood test used to diagnose and monitor Type II diabetes.

By studying genetic variants in 160,000 people from European, African, East Asian and South Asian ancestries, the team found 60 variants that influence the outcome of HbA1c tests.

One genetic variant particular significantly altered the results of the blood glucose test. The variant, found in the G6PD gene, is almost unique to people of African ancestry, the team reported – 11% of African Americans carry at least one copy of this genetic variant.

“The issue with the G6PD genetic variant is it artificially lowers the value of blood sugar in the HbA1c test, and can lead to under-diagnosis of people with Type II diabetes,” joint lead author Dr. Ines Barroso said in prepared remarks. “We estimate that if we tested all Americans for diabetes using the HbA1c test, we would miss Type II diabetes in around 650,000 African Americans. However, the HbA1c test remains a suitable test for diagnosing and monitoring diabetes for the majority of people.”

“The G6PD genetic variant shortens the three-month lifecycle of red blood cells. So in African Americans who have this variant, their red blood cells don’t live long enough to bind to the glucose in the blood,” joint first author Dr. Eleanor Wheeler added. “Therefore these people will have a lower level of HbA1c, which won’t show as a positive result for Type II diabetes.”

“We now need further studies involving people of diverse ancestries to assess how diagnostic tests for diabetes should be altered to account for genetic variation,” joint lead author Dr. James Meigs said. “In the meantime, an option would be to genetically screen African Americans for the G6PD variant alongside the HbA1c test in order to accurately diagnose Type II diabetes, or use other diagnostic tests such as fasting glucose measurements. We suggest moving towards precision medicine to take people’s genetics into account and improve diagnosis and monitoring for diabetes.”

See the best minds in medtech live at DeviceTalks Boston on Oct. 2.