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Time-updated HbA1c more highly linked to MI than baseline HbA1c
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Two time-updated HbA1c metrics appear to demonstrate a stronger association with myocardial infarction compared with baseline HbA1c, according to recent findings.
In the study, Marita Olsson, PhD, of Chalmers University of Technology, and colleagues identified 101,799 patients with type 2 diabetes from the Clinical Practice Research Datalink in the United Kingdom. Patients eligible for the study were diagnosed between 1995 and 2011, and were followed up from the time of diagnosis until MI or the conclusion of the study. Based on time of diagnosis, the researchers identified two subcohorts: an early subcohort including those diagnosed between January 1997 and December 2003 and a recent subcohort including individuals diagnosed between January 2004 and December 2010. The conclusion of follow-up for the early cohort was July 31, 2006 and July 31, 2013 for the recent cohort.
Marita Olsson
The researchers created three HbA1c variables: baseline, updated latest and updated mean. Baseline was the recorded HbA1c value recorded within 90 days before and 30 days after diagnosis. Updated latest HbA1c and updated mean HbA2c were time-varying variables, which were recalculated each time a new HbA1c measurement was taken and chronicled during follow-up. Updated mean HbA1c was the mean of all available measurements of HbA1c.
The researchers used proportional hazard models to evaluate and compare the correlation between each HbA1c variable and MI. They also constructed a basis regression model adjusted for age, systolic blood pressure and MI history; this was fitted for each HbA1c variable.
The researchers found that overall, there was a risk increase for MI per 1% (10 mmol/mol) increase in HbA1c that was higher for updated latest HbA1c of 1.11 (95% CI, 1.09-1.13) and updated mean HbA1c of 1.15 (95% CI, 1.13-1.18) than for baseline HbA1c of 1.05 (95% CI, 1.03-1.06).
The analogous risk estimates in the early subcohort were higher than those in the recent subcohort. When the variables were classified to further explore the shape of the risk curves in relation to MI, the updated last variable showed an increased risk for HbA1c less than 6% (42 mmol/mol) in the recent subcohort (HR = 1.23; 95% CI, 1.08-1.4) but not in the early subcohort (HR = 1.01; 95% CI, 0.84-1.22).
According to the researchers, these findings will be valuable in designing future clinical trials, health-economic models and risk engines.
“In conclusion, the two-time updated HbA1c variables show stronger associations with risk of MI than baseline HbA1c, and the association between HbA1c and risk of MI has decreased over time,” the researchers wrote. “In recently diagnosed patients with type 2 diabetes, an increased risk of MI exists at a current HbA1c level of less than 6% (42 mmol/mol). Our results show that risk estimates of diabetes depend on both HbA1c metric type and temporal aspects of the cohort.” – by Jennifer Byrne
Disclosure: Olsson reports various financial ties with Abbot Scandanavia, AstraZeneca, DexCom, Medtronic, Novo Nordisk and Pfizer. Please see the full study for a list of all other authors’ relevant financial disclosures.
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