Can Diabetes Be Diagnosed With a Single Blood Sample?

Elizabeth Selvin, PhD, MPH; Mark Harmel, MPH


September 20, 2018

Current clinical practice guidelines recommend the use of fasting glucose, hemoglobin A1c, or 2-hour glucose for the diagnosis of diabetes.[1] According to the clinical guidelines, there is no preferred test; however, the guidelines explicitly state that a second test is needed to confirm the diagnosis of diabetes. Additionally, the same test in a second blood sample at a second point in time is recommended to confirm the diagnosis.

To make a diagnosis of diabetes, there needs to be an elevated fasting glucose, elevated hemoglobin A1c, or elevated 2-hour glucose at two separate time points in two separate blood samples. Whether we can make a diagnosis of diabetes using a single blood sample with two elevated test results in that same sample is unknown, but it could streamline the diagnosis of diabetes.

We conducted a prospective cohort study of over 13,000 people and assessed the prognostic validity of a confirmatory definition of diabetes using an elevated hemoglobin A1c and an elevated fasting glucose in a single blood sample.[2] We also evaluated whether that definition of diabetes was associated with prognosis for the future development of diabetes and with diabetic complications, such as kidney disease, heart disease, peripheral arterial disease, and all-cause mortality.

Our results show that this confirmatory definition of diabetes in a single blood sample is highly prognostic and has a high positive predictive value for the diagnosis of diabetes in a community-based population, suggesting that this could be a very efficient approach for the diagnosis of diabetes to complement current clinical practice guidelines. If only one test were elevated and the diagnosis was not confirmed in that single blood sample, the individual could be followed up with a second visit, consistent with current guidelines.

For primary care physicians, this approach can improve the diagnosis process, especially in patients for whom a second visit could be cumbersome, such as in cases where transportation is difficult. The ability to make the diagnosis using information obtained from a single office visit could be highly cost-efficient and help streamline the diagnosis of diabetes.


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