Public health

Single-sample testing would help detect undiagnosed diabetes


A diagnosis of type 2 diabetes could be made from a single blood sample rather than requiring repeat testing on two separate occasions as is currently advised in guidelines, US research suggests.

Researchers at Johns Hopkins Bloomberg School of Public Health have found evidence that elevated levels of fasting glucose (≥7.0 mmol/L and HbA1c (≥6.5%) from a single blood sample is a highly accurate predictor of diabetes and its major diabetes.

Current clinical guidelines recommend that an initial blood test result indicating elevated fasting levels of glucose or HbA1c be confirmed at a second doctor’s visit with another blood test, a practice that the researchers say is time-consuming, relatively expensive and which may lead to missed diagnoses.

Dr Elizabeth Selvin and colleagues in the Department of Epidemiology at the Bloomberg School of Public Health, Baltimore, hypothesized that positive results for both glucose and HbA1c in one blood sample might be an acceptable alternative to the current two-sample standard.

To examine this possibility they undertook a retrospective analysis of data from the long-running Atherosclerosis Risk in Communities (ARIC) Study of the health of more than 13,000 Americans.

The study was designed to find risk factors for atherosclerosis, but it also gathered data relevant to diabetes, including blood glucose and HbA1c test results.

Publishing their findings in Annals of Internal Medicine, the researchers said they identified 978 participants who had elevated levels of fasting glucose or HbA1c at baseline (1990 to 1992). Among these, 39% had both, which they deemed confirmed undiagnosed diabetes, whereas 61% had only one elevated measure, deemed ‘unconfirmed undiagnosed diabetes.

The confirmatory definition had moderate sensitivity (54.9%) but high specificity (98.1%) for identification of diabetes cases diagnosed during the first five years of follow-up, with specificity increasing to 99.6% by 15 years.

The 15-year positive predictive value for diabetes was 88.7% compared with 71.1% for unconfirmed cases.

Confirmed undiagnosed diabetes was significantly associated with cardiovascular and kidney disease and mortality, with stronger associations than unconfirmed diabetes.

“The results of our study suggest that the two tests from one blood sample can provide adequate confirmation of diabetes, potentially allowing a major simplification of current clinical practice guidelines,” said Dr Selvin

“Doctors are already doing these tests together—if a patient is obese, for example, and has other risk factors for diabetes, the physician is likely to order tests for both glucose and HbA1c from a single blood sample,” Dr Selvin added. “It’s just that the guidelines don’t clearly let you use the tests from that one blood sample to make the initial diabetes diagnosis.”

“The bottom line is that this combination of positive results from a single blood sample has a very high positive predictive value for a subsequent diagnosis of diabetes, and also indicates a high risk of typical diabetes complications,” Selvin says.

The study findings could lead to changes in the guidelines to make it possible for diabetes to be diagnosed more quickly based on the two positive results in one blood sample, she suggested.

“I’m hoping that these results will lead to a change in the clinical guidelines when they are revised in early 2019, which could make identifying diabetes a lot more efficient in many cases,” Dr Selvin said.

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