Diabetes test may result in incorrect reading

Author: Tamar Kahn

Source: Business Day

PEOPLE of African descent may mistakenly get the all-clear from a widely used type 2 diabetes test – called HbA1c – according to an international study published in PLOS Medicine. Scientists found 42 new genetic variants that influence a person’s HbA1c measurements, including one that could lead to Africans and African-Americans being underdiagnosed with type 2 diabetes.

University of the Witwatersrand endocrinologist, Alisha Wade, said the findings have important implications, as they suggest that using this test as the sole means to diagnose diabetes would do harm. She said recent World Health Organisation recommendations cite HbA1c as a method for the diagnosis of diabetes in addition to more conventional methods of testing blood sugar in a fasted state or after an oral glucose challenge. There is substantial debate about use of HbA1c for diagnosis as there are known ethnic variations in the relationship between HbA1c and blood sugar, and the majority of studies to date have been done in populations of European origin.

Wade said this study provides a genetic explanation for why we should continue to be cautious about a wholesale shift to HbA1c for diabetes. The Society for Endocrinology, Metabolism and Diabetes of SA’s guidelines recommend HbA1c for diagnosing type 2 diabetes only if there are no haemoglobin abnormalities, but screening for these abnormalities is not routinely done in SA, Wade said.

The HbA1c test is used to diagnose type 2 diabetes and assess blood sugar control in patients who have already been diagnosed. A person’s level of HbA1c, or glycated haemoglobin, depends on both blood glucose levels and characteristics of their red blood cells. The scientists found a variant in the G6PD gene, which encodes an enzyme related to the life-span of red blood cells, and lowers HbA1c levels no matter the blood glucose level. Their analysis included almost 160 000 individuals of European, African, East Asian and South Asian ancestry, 33 000 of whom went on to develop type 2 diabetes. They found about 11 percent of African-Americans carried at least one copy of this G6PD variant, while almost no one of any other ancestry did. It means the test would miss about 650 000 African-Americans because of their genetically lowered HbA1c levels if it were given to all Americans, according to the study’s lead authors. The research, which identified 60 genetic variants that influence a person’s HbA1c measurement found people who had more genetic variants that change HbA1c levels through effects on blood glucose levels were at increased risk of developing diabetes over time.