A New Zealand Linkage Study Examining the Associations Between A1C Concentration and Mortality

Abstract

OBJECTIVE -To examine associations between A1C concentration and mortality in a New Zealand population. (1999 -2001), participants were offered A1C testing. The participants were anonymously linked to the national mortality collection to 31 December 2004. Hazard ratios (HRs) and 95% CIs adjusted for age, ethnicity, smoking, and sex were estimated using Cox regression. RESEARCH DESIGN AND METHODS -During a HepatitisFoundation screening campaign for hepatitis BRESULTS -There were 47,904 participants (71% Mâori, 12% Pacific, 5% Asian, and 12% other). A1C measurements were categorized as Ͻ4.0% (n ϭ 142), 4.0 to Ͻ5.0% (reference category; n ϭ 12,867), 5.0 to Ͻ6.0% (n ϭ 30,222), 6.0 to Ͻ7.0% (n ϭ 2,669), and Ն7.0% (n ϭ 1,596); there were also 408 participants with a previous diabetes diagnosis. During the follow-up period, 815 individuals died. In those without a prior diabetes diagnosis, there were steadily increasing HRs from the A1C reference category to the highest category (Ն7.0%; HR 2.36 [95% CI 1.72-3.25]). As well as all-cause mortality, A1C was associated with mortality from diseases of the circulatory system; endocrine, nutritional, metabolic, and immunity disorders; and other and unknown causes. Mortality was also elevated in those with a prior diabetes diagnosis (5.19 [3.67-7.35]), but this was only partially explained by their elevated A1C levels.CONCLUSIONS -This is the largest study to date of A1C levels and subsequent mortality risk. It confirms previous findings that A1C levels are strongly associated with subsequent mortality in both men and women without a prior diabetes diagnosis.

Continuous relationships between non-diabetic hyperglycaemia and both cardiovascular disease and all-cause mortality: the Australian Diabetes, Obesity, and Lifestyle (AusDiab) study

“…Several studies reported a consistent graded relationship between HbA 1c and both all-cause mortality [16,18,37,38] and fatal and/or non-fatal CVD [16,18]. In contrast, Selvin et al [7] found that the risk of coronary heart disease only increased above an HbA 1c of 4.6%.…”

No evidence of an increased mortality risk associated with low levels of glycated haemoglobin in a non-diabetic UK population

“…There is broad evidence for hyperglycaemia as a risk factor for cardiovascular disease [15,16], extended very recently by results of a large collaborative meta-analysis of 102 studies on fasting glucose concentrations [17], but data on the low range of glycaemia are inconsistent. In addition to the ARIC study and NHANES, four earlier studies reported mortality risk for categories of glycated haemoglobin in non-diabetic populations, with one study suggesting a potentially increased risk [8] and three studies suggesting no increased risk with low levels of glycated haemoglobin [6,7,9]. However, low numbers of events, particularly in the low range of glycated haemoglobin (below~5.0%), limit an accurate risk estimation in these studies.…”

“…Most previous studies examining the association of glycated haemoglobin with all-cause mortality in nondiabetic populations have had limited statistical power to test the nature of the association at the low end of the distribution [6][7][8][9]. Therefore, in order to test the shape of association and explore potential underlying mechanisms, we analysed the association of glycated haemoglobin with all-cause and cause-specific mortality in men and women in a UK population-based study.…”

HbA1c as predictor of all-cause mortality in individuals at high risk of diabetes with normal glucose tolerance, identified by screening: a follow-up study of the Anglo–Danish–Dutch Study of Intensive Treatment in People with Screen-Detected Diabetes in Primary Care (ADDITION), Denmark

“…Some studies have demonstrated that HbA 1c is a risk factor for all-cause mortality in individuals with no prior diagnosis of diabetes [4][5][6][7][8]. In stepwise screening for type 2 diabetes mellitus, HbA 1c is often measured.…”