Prognostic Implications of Single-Sample Confirmatory Testing for Undiagnosed Diabetes A Prospective Cohort Study

Background:

Current clinical definitions of diabetes require repeated blood work to confirm elevated levels of glucose or hemoglobin A_1c (HbA_1c) to reduce the possibility of a false-positive diagnosis. Whether 2 different tests from a single blood sample provide adequate confirmation is uncertain.

Objective:

To examine the prognostic performance of a single-sample confirmatory definition of undiagnosed diabetes.

Design:

Prospective cohort study.

Setting:

The ARIC (Atherosclerosis Risk in Communities) study.

Participants:

13 346 ARIC participants (12 268 without diagnosed diabetes) with 25 years of follow-up for incident diabetes, cardiovascular outcomes, kidney disease, and mortality.

Measurements:

Confirmed undiagnosed diabetes was defined as elevated levels of fasting glucose (≥7.0 mmol/L [≥126 mg/dL]) and HbA_1c (≥6.5%) from a single blood sample.

Results:

Among 12 268 participants without diagnosed diabetes, 978 had elevated levels of fasting glucose or HbA_1c at baseline (1990 to 1992). Among these, 39% had both (confirmed undiagnosed diabetes), whereas 61% had only 1 elevated measure (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 5 years of follow-up, with specificity increasing to 99.6% by 15 years. The 15-year positive predictive value 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.

Limitation:

Lack of repeated measurements of fasting glucose and HbA_1c.

Conclusion:

A single-sample confirmatory definition of diabetes had a high positive predictive value for subsequent diagnosis and was strongly associated with clinical end points. Our results support the clinical utility of using a combination of elevated fasting glucose and HbA_1c levels from a single blood sample to identify undiagnosed diabetes in the population.

Primary Funding Source:

National Institute of Diabetes and Digestive and Kidney Diseases and National Heart, Lung, and Blood Institute.

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