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Why a key diabetes test may work differently depending on your race

Jacqueline Howard, CNN | 6/29/2017, 5:18 p.m.
A test widely used to diagnose and monitor diabetes may vary in accuracy based on your race and other factors, ...
Diabetes Pixabay

(CNN) -- A test widely used to diagnose and monitor diabetes may vary in accuracy based on your race and other factors, potentially influencing how aggressively your doctor monitors and treats your diabetes.

The hemoglobin A1c test measures the average level of sugar, or glucose, attached to a protein in your red blood cells called hemoglobin. The test gauges that average over the previous three months or so.

Yet scientists have long speculated that hemoglobin A1c levels can vary depending on your race or genetics, which could interfere with your test results and lead health care providers to think your blood sugar is higher or lower than it really is.

People of African, Mediterranean or Southeast Asian descent are particularly at risk of interference, according to the National Institute of Diabetes and Digestive and Kidney Diseases. People who have family members with sickle cell anemia or an inherited blood disorder called thalassemia also can be at risk.

A new study of patients with type 1 diabetes looked into such interference, specifically for black patients. The study, published in the journal Annals of Internal Medicine on Monday, suggests that hemoglobin A1c levels can overestimate the average glucose concentration in black patients, compared with white patients.

This overestimate could lead a doctor to target a black patient's blood sugar levels aggressively, causing dangerously low blood sugar.

"I believe our study, for the first time, definitively shows there is a component of higher A1c that is due to biologic or genetic differences in glucose attaching to the red blood cell," said Dr. Richard Bergenstal, executive director of the International Diabetes Center in Minneapolis and lead author of the study.

The study notes that race only partially explains the hemoglobin A1c differences, and more research is needed to identify social and economic factors that may influence blood sugar levels in various groups of people.

For black patients in America, who have traditionally faced a history of barriers and disadvantages in health care, those factors might also include having limited access to care or medications.

Bergenstal offered one specific question that concerned patients could ask their doctors: "Are we depending just on the hemoglobin A1c to measure how my diabetes control is doing, or are we actually looking at the blood sugars to get a little better reflection of my blood sugars?"

He added that "the A1c, you know, is kind of an average marker, and no patient is average. One of our take-home messages is, it's probably time to be looking at blood sugars and personalizing therapy for each individual a little more than just this average blood sugar test."

Many US adults who have diabetes don't know it

Diabetes is a disease in which your blood sugar levels are above normal, which could cause health problems. With type 1 diabetes, your pancreas does not make insulin, a hormone that helps glucose get into your cells to give them energy. Type 2 diabetes results primarily from your body's ineffective use of insulin.

Globally, the number of people with type 1 and type 2 diabetes has climbed from 108 million in 1980 to 422 million in 2014, according to the World Health Organization.