Hemoglobin A1C Levels Strongly Linked to Subsequent Mortality in Diabetes CME/CE
News Author: Laurie Barclay, MD
CME Author: Laurie Barclay, MD
Authors and Disclosures
CME/CE Released: 06/09/2008; Valid for credit through 06/09/2009
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June 9, 2008 Hemoglobin A1C (A1C) levels are strongly associated with subsequent mortality in both men and women without a previous diabetes diagnosis, according to the results of the largest study to date of A1C levels and subsequent mortality risk, reported in the June issue of
Diabetes Care.
"Only a few prospective studies have examined the associations between A1C among subjects initially free of diabetes and subsequent risk of mortality," write Naomi Brewer, MMedSci, from the Centre for Public Health Research, Massey University in Wellington, New Zealand, and colleagues. "Each of these studies found associations with subsequent mortality. A1C levels have also been associated with mortality in patients with type 1 diabetes and nondiabetic chronic kidney disease and with incident cardiovascular disease."
The goal of this study was to evaluate the association between A1C concentration and mortality rate in a New Zealand population. From 1999 to 2001, participants were offered A1C testing during a Hepatitis Foundation screening campaign for hepatitis B. These participants were anonymously linked to the database for national mortality through December 31, 2004. Cox regression was used to estimate hazard ratios (HRs) adjusted for age, ethnicity, smoking, and sex.
Of 47,904 participants, 71% were Mâori, 12% Pacific, 5% Asian, and 12% other. A1C was less than 4.0% in 142 participants, 4.0% to less than 5.0% (reference category) in 12,867, 5.0% to less than 6.0% in 30,222, 6.0% to less than 7.0% in 2669, and 7.0% or higher in 1596 participants. In addition, 408 participants had a previous diagnosis of diabetes.
During follow-up, there were 815 deaths. For participants without a previous diagnosis of diabetes, HRs for all-cause mortality steadily increased from the A1C reference category to the highest category (≥ 7.0%; HR, 2.36; 95% confidence interval [CI], 1.72 - 3.25). In addition, A1C was associated with mortality from circulatory, endocrine, nutritional, metabolic, and immune diseases as well as from other and unknown causes. Although mortality rate was also increased in participants with a previous diagnosis of diabetes, this was only partially explained by their increased A1C levels.
"This is the largest study to date of A1C levels and subsequent mortality risk," the study authors write. "It confirms previous findings that A1C levels are strongly associated with subsequent mortality in both men and women without a prior diabetes diagnosis."
Limitations of this study include lack of anthropometric data and information on other cardiovascular risk factors; short follow-up time; inability to exclude the possibility that diabetes at the time of the A1C test might have led to increased glucose levels; misclassification of specific causes of death; and participants being enrolled in an intensive population-based hepatitis B screening program, which may prevent generalizability of the findings to the overall population.
"The excess mortality risk was from a range of causes but was particularly strong for endocrine, nutritional, and metabolic and immunity disorders and for cardiovascular disease," the study authors conclude. "However, A1C levels only partially accounted for the excess mortality risk in participants with a previous diagnosis of diabetes."
The Health Research Council of New Zealand supported the Centre for Public Health Research and the Research Centre for Mâori Health and Development. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC Section 1734 solely to indicate this fact.
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