a1c test tube in front of bullseye; a1c test unreliable for diagnosis

A1c Test Found to be Unreliable to Diagnose Diabetes

Researchers from the City of Hope’s Diabetes and Metabolism Research Institute in Duarte, California have concluded that the A1c test commonly used to test for diabetes is not a reliable method of diagnosis on its own.

What is the A1c test?

The A1c test (also known as the HbA1c or glycated hemoglobin test) is used to measure a person’s average blood sugar level over the previous three months. Blood sugar levels can vary depending on the time of day, activity levels, hormonal changes, and the person’s dietary intake. For this reason, the A1c test is used frequently for diagnosis because it resists factors that could influence short-term tests. Another reason it is used frequently is because it does not require the patient to fast beforehand unlike other diabetes tests.


The study

Researchers tested 9,000 adults with no previous diabetes diagnosis using the A1c test and oral glucose tolerance test (OGTT). The results were alarming: the A1c test missed 73 percent of diabetes cases that were found using the oral glucose test.

Lead researcher Dr. Maria Mercedes Chang Villacreses said, “Our results indicated that the prevalence of diabetes and normal glucose tolerance defined solely by A1c is highly unreliable, with a significant tendency for underestimation of the prevalence of diabetes and overestimation of normal glucose tolerance.”

Influences of inaccurate testing

Although the A1c test is considered the most reliable way to diagnose diabetes due to its view of long-term blood sugar levels, there are several factors that can influence test results. Blood transfusions and heavy or chronic bleeding can create falsely low results, while anemia can create a falsely high result.

A person’s race can also influence test results, as indicated by the aforementioned study. Some people may have a hemoglobin variant that could create an inaccurate test result. This is most common in people of African, Mediterranean, and Southeast Asian descent. If you have a hemoglobin variant, your A1c test will need to be performed at a specialized lab to ensure accurate results.


What to make of your A1c test results

Your A1c levels should be tested as frequently as your doctor deems necessary, but those with type 2 diabetes will usually be tested twice per year, and those with type 1 diabetes will be tested about once every three months.

A1c test ranges:

  • Normal: 5.6% or below
  • Prediabetes: 5.7-6.4%
  • Diabetes 6.5% or higher

A1c levels above 8 percent suggest your diabetes is not properly controlled and you are at risk of developing diabetes complications like kidney, heart, and eye disease. Your doctor will work with you to determine your A1c goal, but many people with diabetes aim for 7 percent or less.

If you are concerned about inaccurate A1c test results, talk to your doctor about your concerns and ask if a secondary test is available.