Using the A1C test — a measure of long-term blood glucose control — as a screening test may help identify cases of undiagnosed diabetes more quickly, according to a new analysis published in the journal Diabetologia.
While A1C has long been used as a blood test to evaluate blood glucose control in people with diagnosed diabetes, it’s only in fairly recent years that it has been recommended as a diagnostic test — with an A1C level of 6.5% or higher indicating diabetes, and a level of 5.7% to 6.4% indicating prediabetes. Before 2018, all A1C testing methods approved for diagnosing diabetes involved processing blood samples in a central laboratory, but that year, the first rapid A1C test for diagnosis was approved — making it possible to diagnose diabetes more quickly than ever before. But using A1C as a diagnostic test — compared with longstanding methods like an oral glucose tolerance test (OGTT) or a fasting blood glucose test — isn’t without potential downsides. Research has shown that compared with other methods, A1C may miss some cases of diabetes. For reasons that aren’t entirely clear, A1C may be less reliable as a diagnostic test for people of African descent than for other racial or ethnic groups.
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For the latest analysis, researchers looked at data from nearly 180,000 people ages 40 to 70 who enrolled in a general health study called the UK Biobank. Participants had their A1C level measured at the time of enrollment, but this result wasn’t shared with participants or with their doctors. Just over 13,000 of these participants, or 7.3%, were already diagnosed with diabetes when they enrolled in the study, based on a review of their health records. Among the remaining roughy 167,000 participants without a diabetes diagnosis, the researchers compared A1C at the time of enrollment with whether participants were diagnosed with diabetes — outside of the study — within the next 10 years.
A1C test useful for detecting undiagnosed diabetes
Overall, 1.0% of participants without a diabetes diagnosis at the time of enrollment were found to have undiagnosed diabetes, based on their A1C level at the time of enrollment Among these participants, the median A1C level was 6.8% — slightly above the cutoff for a diabetes diagnosis. Relative to participants who were already diagnosed with diabetes, those with undiagnosed diabetes represented an additional 13.0% of diabetes cases — not a trivial number. For participants with undiagnosed diabetes, the median duration between enrollment in the study and finally receiving a diabetes diagnosis was 2.2 years — time in which people could have been working to control their diabetes, if they knew they had it. By the time they got a diagnosis, these participants’ median A1C level was 7.5%. But as noted in an article on the analysis at Healio, just 87.7% of participants with undiagnosed diabetes ended up receiving a diagnosis within 10 years — meaning that 12.3% of these participants had diabetes but didn’t receive a diagnosis for a decade or longer, and possibly never.
The researchers also found that using just age or body-mass index (BMI, a measure of body weight that takes height into account) to decide who should get screening for diabetes — and receive an A1C test — would miss more than 40% of undiagnosed diabetes cases. Using what’s known as validated risk scores — which estimate the risk for developing diabetes based on several available factors — did better, with the ADA Risk Score missing 23.3% of undiagnosed diabetes cases, the Leicester Risk Score missing 15.7% of undiagnosed cases, and the Finnish Diabetes Risk Score missing 7.8% of undiagnosed cases when the lowest potential cutoff score was used.
These findings “support the use of [A1C] screening to reduce the time for which individuals are living with undiagnosed diabetes,” the researchers concluded, while noting that there is still debate regarding who, exactly, should be screened for diabetes and when.
Want to learn more about A1C? Read “How to Lower A1C Levels Naturally,” “How to Lower Your A1C Levels: More Steps You Can Take” and “Getting Your A1C to Target.”
