ORIGINAL CONTRIBUTIONS |
Seasonal Patterns in Monthly Hemoglobin A1c Values
1 Center for Health Care Knowledge Management, Department of Veterans Affairs New Jersey Health Care System, East Orange, NJ
2 Department of Preventive Medicine and Community Health, University of Medicine and Dentistry of New Jersey-New Jersey Medical School, Newark, NJ
3 Department of Statistics, Rutgers University, New Brunswick, NJ
4 Health Services Research Institute for Health, Health Care Policy, and Aging Research, Rutgers University, New Brunswick, NJ
5 CTC Technologies, Inc., Short Hills, NJ
6 Department of Medicine, University of Medicine and Dentistry of New Jersey-New Jersey Medical School, Newark, NJ
7 Birmingham VA Medical Center, Birmingham, AL
Correspondence to Dr. Chin-Lin Tseng, Department of Veterans Affairs New Jersey Health Care System, East Orange VA Medical Center, 385 Tremont Avenue, #129, East Orange, NJ 07018 (e-mail: Tseng{at}njneuromed.org).
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.
diabetes mellitus; hemoglobin A, glycosylated; seasons; veterans
Abbreviations: A1c hemoglobin A1c
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