A1c Test Results Associated With Cardiovascular Death

A New Zealand linkage study examining the associations between glycosylated hemoglobin concentration and mortality regardless of the diagnosis of diabetes

To examine associations between glycosylated hemoglobin (HbA1c) concentration and mortality in a New Zealand population, participants during a Hepatitis Foundation screening campaign for hepatitis B were offered hbA1c testing.The participants were anonymously linked to the national mortality collection to 31st December 2004. Hazard ratios (HRs) and 95% confidence intervals (95%CI) adjusted for age, ethnicity, smoking and gender were estimated using Cox regression.
There were 47,904 participants (71% Mori, 12% Pacific, 5% Asian, 12% Other). HbA1c measurements were categorized as: <4.0% (n=142); 4.0–<5.0% (reference category; n=12,867); 5.0–<6.0% (n=30,222); 6.0–<7.0% (n=2,669); 7.0% (n=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 HbA1c reference category to the highest category (7.0%; HR 2.36, 95%CI 1.72–3.25).

As well as all cause mortality, HbA1c was associated with mortality from diseases of the circulatory system, endocrine, nutritional and metabolic and immunity disorders, and other and unknown causes’. Mortality was also elevated in those with a prior diabetes diagnosis (HR 5.19, 95%CI 3.67–7.35), but this was only partially explained by their elevated HbA1c levels.
This is the largest study to date of HbA1c levels and subsequent mortality risk. It confirms previous findings that HbA1c levels are strongly associated with subsequent mortality in both men and women without a prior diabetes diagnosis.

Diabetes Care, Feb 2007