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A widely used blood test for diabetes can give variable results depending on a person's race and other factors. This means diabetes can sometimes be misdiagnosed or managed poorly, as NPR's Richard Harris reports.
RICHARD HARRIS, BYLINE: Blood sugar levels rise and fall all the time, so it can be tricky to look at a single exam to diagnose diabetes or manage the disease in people who have it. But one test gets around this problem. Dr. Anthony Bleyer at the Wake Forest School of Medicine says the A1C test takes the long view.
ANTHONY BLEYER: And it actually gives us an average of the blood glucose over the past three months. So this has turned out to be an incredibly powerful test both for the diagnosis and the treatment of diabetes.
HARRIS: And the assumption is that everybody is pretty much the same, right? And is that true?
BLEYER: That's the problem - no. That's the problem - is everybody is not the same, and it's a little more complicated than that.
HARRIS: People with anemia, for example, get different readings on the test. And a few years ago, scientists realized that African-American readings don't match those from whites.
BLEYER: So the test was really standardized more based on white individuals, and there were just a small number of African-American individuals in that study.
HARRIS: And while the difference isn't large, it can matter for borderline readings, which are fairly common. It can also be misleading for people whose treatment is guided by the test because doctors may be too aggressive in managing blood sugar based on a too-high reading.
Now there's a study that looks more closely at how much the test can vary among people who carry a common genetic pattern - sickle cell trait. About 10 percent of African-Americans carry one copy of the sickle cell gene, giving them the trait but not the disease.
MARY LACY: And so we thought maybe sickle cell trait could be explaining part of the difference.
HARRIS: Mary Lacy is a graduate student at Brown University and lead author of the new report in JAMA. She and her colleagues examined two large studies to compare African-Americans with and without the sickle cell trait. The studies use certain A1C tests that had previously been shown to give low readings for people with a sickle cell trait. Lacy and colleagues were surprised to find how big a difference it made.
About 4 percent of the people in the study who carried the sickle cell trait had readings indicative of diabetes, but they expect the real number, correcting for the test, could be about 7 percent, nearly twice as many people.
LACY: We were really shocked by that, honestly. That's huge.
HARRIS: The lesson here is doctors should be cautious when interpreting a patient A1C results, especially for African-Americans.
MARA DARSOW: Doctors generally take the test fairly literally.
HARRIS: Mara Darsow is at the American Diabetes Association. Taking results literally can be a mistake.
DARSOW: How much this impacts care and the interpretation of A1C results I think is variable.
HARRIS: Doctors who read the fine print in her organization's guidelines know that these test readings can be skewed for African-Americans and people with sickle cell trait and similar variants. So instead of making a snap diagnosis, doctors could run some more traditional blood sugar tests. They aren't influenced by race and sickle cell status.
DARSOW: Information together from all of these tests can be really much more powerful than when they're taken in isolation.
HARRIS: The Diabetes Association would ultimately like to come up with more concrete treatment guidelines. But for now, the word to doctors is, be aware this is an issue, and use your best judgment. Richard Harris, NPR News.
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