One of the most popular methods of diagnosing type 2 diabetes is the HbA1c test. HbA1c is a modified form of hemoglobin which is produced during periods of high blood sugar levels. A diagnosis of diabetes will often rely on a test of how elevated the levels of HbA1c are present in the blood.
A recent study however has called into question the reliability of this test. An international team of researchers undertook a genome-wide analysis of 160,000 people from a variety of different ethnic backgrounds.
Perhaps the most startling of their findings was the fact that amongst people with African-American ancestry, the level of HbA1c detected by the test was not a reliable indicator of whether someone had diabetes or not.
They discovered that about 11% of people of African American ancestry carry a variant of a gene called G6PD. This variant can shorten the lifespan of red blood cells (which carry the HbA1c protein) in the blood, and so lower the level of HbA1c present- no matter what the blood glucose level is. This genetic variant is very rare in any other ethnic groups.
The study estimated 650,000 African-Americans may have been incorrectly diagnosed as being free from type 2 diabetes if they were screened only using the HbA1c test.