Journal Article

Seasonal Patterns in Monthly Hemoglobin A<sub>1c</sub> Values

Chin-Lin Tseng, Michael Brimacombe, Minge Xie, Mangala Rajan, Hongwei Wang, John Kolassa, Stephen Crystal, Ting-Cheng Chen, Leonard Pogach and Monika Safford

in American Journal of Epidemiology

Published on behalf of Johns Hopkins Bloomberg School of Public Health

Volume 161, issue 6, pages 565-574
Published in print March 2005 | ISSN: 0002-9262
Published online March 2005 | e-ISSN: 1476-6256 | DOI:
Seasonal Patterns in Monthly Hemoglobin A1c Values

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The purpose of this study was to investigate seasonal variations in population monthly hemoglobin A1c (A1c) values over 2 years (from October 1998 to September 2000) among US diabetic veterans. The study cohort included 285,705 veterans with 856,181 A1c tests. The authors calculated the monthly average A1c values for the overall population and for subpopulations defined by age, sex, race, insulin use, and climate regions. A1c values were higher in winter and lower in summer with a difference of 0.22. The proportion of A1c values greater than 9.0% followed a similar seasonal pattern that varied from 17.3% to 25.3%. Seasonal autoregressive models including trigonometric function terms were fit to the monthly average A1c values. There were significant seasonal effects; the seasonal variation was consistent across different subpopulations. Regions with colder winter temperatures had larger winter-summer contrasts than did those with warmer winter temperatures. The seasonal patterns followed trends similar to those of many physiologic markers, cardiovascular and other diabetes outcomes, and mortality. These findings have implications for health-care service research in quality-of-care assessment, epidemiologic studies investigating population trends and risk factors, and clinical trials or program evaluations of treatments or interventions.

Keywords: diabetes mellitus; hemoglobin A, glycosylated; seasons; veterans; A1c    hemoglobin A1c

Journal Article.  7008 words.  Illustrated.

Subjects: Public Health and Epidemiology

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