Using the hemoglobin A1c to diagnose diabetes tends to underestimate the prevalence of the disease, suggests a study presented at ENDO 2019, the Endocrine Society’s annual meeting in New Orleans, Louisiana.
In the study, 9,000 adults without a diabetes diagnosis were randomized to an A1c test and an oral glucose tolerance test (OGTT). Comparison of the results showed that using A1c as a diagnostic test missed about 73% cases of diabetes that were detected by OGTT. Race and ethnicity were found to have a significant impact on the accuracy of the test. A1c was more likely to detect abnormal glucose levels in non-Hispanic whites than in non-Hispanic blacks or Hispanics.
As per the authors of the study, A1c, when used solely to define diabetes is a highly unreliable test and significantly underestimates the prevalence of diabetes. A1c should be used along with OGTT for improved accuracy of detection.
The American Diabetes Association recommends measuring HbA1c to diagnose prediabetes and diabetes due to its “greater convenience (fasting not required), greater preanalytical stability and less day-to-day perturbations during stress and illness.” HbA1c value of ≥6.5% has been established as the diagnostic figure associated with diabetes.
However, A1c has lower sensitivity to diagnose diabetes. A1c can give false results in some people.
- People of African, Mediterranean, or Southeast Asian descent, or people with family members with sickle cell anemia or a thalassemia are particularly at risk of interference. People in these groups may have a less common type of hemoglobin, known as a hemoglobin variant that can interfere with some A1c tests.
- A falsely low A1c result may be seen in people with anemia, heavy bleeding.
- A falsely high A1c result is seen in individuals who are very low in iron, e.g., those with iron deficiency anemia.