Single blood sample can identify undiagnosed diabetes

June 19, 2018   /

By Will Boggs MD

NEW YORK (Reuters Health) - Fasting glucose and hemoglobin A1c (HbA1c) measured in a single blood sample can be used to identify individuals with undiagnosed diabetes, according to results from the Atherosclerosis Risk in Communities (ARIC) study.

"It is common for physicians to measure two laboratory tests - such as fasting glucose and HbA1c - in a single blood sample," said Dr. Elizabeth Selvin from Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, in an email to Reuters Health. "Our results suggest that a single-sample definition of diabetes is a streamlined process for diagnosis. Patients with single elevations in HbA1c or fasting glucose ('unconfirmed cases') should have their tests repeated at a second time point, consistent with current clinical practice guidelines."

American Diabetes Association guidelines recommend repeating one of these tests in a new blood sample at a different time to confirm the diagnosis of diabetes, but whether performing both tests in the same blood sample can provide adequate confirmation remains uncertain.

Dr. Selvin and colleagues used data from 13,346 ARIC participants to evaluate the prognostic performance of single-sample confirmatory definitions of undiagnosed diabetes. They defined confirmed undiagnosed diabetes as fasting glucose levels of 7 mmol/L (126 mg/dL) or higher and HbA1c levels of 6.5% or higher. Unconfirmed undiagnosed diabetes was defined as elevations in fasting glucose or HbA1c (not both).

Overall, 4% of the population had isolated fasting glucose elevation and 1% had isolated HbA1c elevation at baseline. Among the 978 individuals with elevations of fasting glucose or HbA1c, 39% had confirmed undiagnosed diabetes and 61% had unconfirmed undiagnosed diabetes, according to a report online June 18 in Annals of Internal Medicine.

The cumulative incidence of future diagnosed diabetes in the confirmed undiagnosed group was 42.0% at 5 years and 97.3% at 15 years, compared with only 9.9% and 71.7%, respectively, in the unconfirmed undiagnosed group.

Confirmed undiagnosed diabetes was also associated with high rates of chronic kidney disease, cardiovascular disease, peripheral artery disease, and mortality during follow-up.

In adjusted models, confirmed undiagnosed diabetes was associated with a 25-fold increased risk of diagnosed diabetes, whereas unconfirmed undiagnosed diabetes was associated with a 5.75-fold increased risk.

In the unconfirmed undiagnosed diabetes group, isolated elevated HbA1c levels were associated with higher absolute risks of a future diagnosis of diabetes, incident chronic kidney disease, incident cardiovascular disease, peripheral artery disease, and all-cause mortality, compared with isolated elevated fasting glucose levels.

"Our study demonstrates that two tests (HbA1c and fasting glucose) from the same blood sample provide adequate confirmation for diagnosis," Dr. Selvin said. "We hope that this research will impact guidelines for how diabetes is diagnosed in the U.S."

Dr. K. M. Venkat Narayan and Dr. Ram Jagannathan from Emory University, Atlanta, Georgia, who wrote an editorial related to this report, told Reuters Health in a joint email, "Even elevation of HbA1c or fasting plasma glucose (FPG) at a single time point is associated with increased risk of progression to overt diabetes and to complications. Therefore, anyone testing abnormal on any glucose test needs to be followed up with