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. 2015 Apr 8;10(4):e0122698.
doi: 10.1371/journal.pone.0122698. eCollection 2015.

Incidence of type 2 diabetes in pre-diabetic Japanese individuals categorized by HbA1c levels: a historical cohort study

Tetsuya Kawahara  1 , Ryuichiro Imawatari  2 , Chie Kawahara  3 , Tetsuya Inazu  4 , Gen Suzuki  5
Affiliations

Incidence of type 2 diabetes in pre-diabetic Japanese individuals categorized by HbA1c levels: a historical cohort study

Tetsuya Kawahara et al. PLoS One. .

Abstract

Objective: Reported incidence of type 2 diabetes estimated at the pre-diabetic stage differs widely (2.3-18.1% per year). Because clinicians need to know the risk of incident diabetes after a diagnosis of pre-diabetes, our objective was to estimate precise incidence of diabetes using baseline HbA1c levels.

Methods: A historical cohort study using electronic medical record data obtained between January 2008 and December 2013. A total of 52,781 individuals with HbA1c < 6.5% were assigned to one of six groups categorized by baseline HbA1c level: ≤ 5.5% (n=34,616), 5.6-5.7% (n=9,388), 5.8-5.9% (n=4,664), 6.0-6.1% (n= 2,338), 6.2-6.3% (n=1,257), and 6.4% (n=518). Participants were tracked until a subsequent diagnosis of diabetes or end of follow-up during a period of 5 years.

Results: During the follow-up period (mean 3.7 years), 4,369 participants developed diabetes. The incidence of diabetes in the first year was 0.7, 1.5, 2.9, 9.2, 30.4, and 44.0% in the six HbA1c groups, respectively. At five years the incidence was 3.6, 8.9, 13.8, 27.5, 51.6, and 67.8%, respectively (p < 0.0001 comparing the HbA1c ≤5.5% group to the other groups). After adjustment for confounding factors, the hazard ratios compared with the HbA1c ≤5.5% group were significantly elevated: 2.3 (95%CI 2.0-2.5), 3.4 (95%CI 2.9-3.7), 8.8 (95%CI 8.0-10.1), 26.3 (95%CI 23.3-30.1), and 48.7 (95%CI 40.8-58.1) in the five HbA1c groups (p < 0.0001).

Conclusion: By fractionating baseline HbA1c levels into narrower HbA1c range groups, accuracy of estimating the incidence of type 2 diabetes in subsequent years was increased. The risk of developing diabetes increased with increasing HbA1c levels, especially with the HbA1c level ≥ 6.2% in the first follow-up year.

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Conflict of interest statement

Competing Interests: RI is an employee of Kokura Medical Association of Health Testing Center, a unit of Kokura Medical Association and a member of Kitakyushu Medical Association Committee on Health Promotion, a unit of Kitakyushu Medical Association. Since Kokura ward is a subdivision of Kitakyushu city, Kokura Medical Association has affiliation with Kitakyushu Medical Association. This does not alter the authors' adherence to PLOS ONE policies on sharing data and materials.

Figures

Fig 1
Fig 1. Kaplan—Meier survival curves for incident diabetes during the 5-year study period, differentiated by baseline HbA1c levels.
Each curve had a significantly higher risk compared with the reference group, the curve for HbA1c ≤ 5.5% (log-rank P value <0.0001).
See this image and copyright information in PMC

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