medwireNews: Variability in glycated hemoglobin (HbA1c) may be more important than the average level for predicting mortality in people with type 2 diabetes, an analysis of UK primary care data shows.
Julia Critchley and colleagues from St George’s University of London in the UK note, however, that the highest average HbA1c levels were also associated with increased mortality, while both high average HbA1c and increasing HbA1c variability predicted hospital admission.
They therefore write in Diabetes Care that treatment “[t]argets should focus on both stability and absolute level of HbA1c.”
The study included 58,832 patients (mean age 68 years, 55.3% men) with type 2 diabetes who had their HbA1c average (mean of annual means), variability (coefficient of variation [CoV]), and trajectory (annual regression slope) estimated during a 4-year period (2006–2009).
During this run-in period, patients provided a mean 7.9 HbA1c measurements, with a mean level of 7.4% and a slight downward trend over time (0.01% per year).
The researchers found that in models adjusted for HbA1c variability, average, and trajectory, the risk for mortality increased with increasing HbA1c variability.
Specifically, the hazard ratio (HR) for death was 1.32 for individuals in the 25th–50th percentile for variability (CoV >4.71–7.33) relative to those in the 10th percentile (CoV 0–3.14), but increased to 1.93 for individuals in the 90th percentile for variability (CoV >16.61).
The association was attenuated after accounting for hypoglycemia, to a HR of 1.67 in the 90th percentile, but Critchley and co-authors say that “variability still maintained a stronger and more consistent association with mortality than average HbA1c.”
Indeed, the impact of HbA1c on mortality was only significant in the top and bottom 10%, with HRs of 1.14 and 1.35, respectively, when compared with the 10th–25th percentile group.
By contrast, HbA1c trajectory had no independent effect on mortality.
Critchley and co-investigators observed similar patterns for first emergency hospitalizations
One exception to the pattern for both mortality and hospitalization was observed, however. For coronary artery disease and ischemic stroke, increasing average HbA1c rather than variability was more strongly associated with hospitalization for or death from these causes.
Critchley et al conclude: “Current guidelines promote both lower levels of HbA1c and stability of HbA1c, but tend to prioritize the former, while our analyses generally suggest that more importance should be given to stability for many patients.”
They add: “Measurements of variability could be incorporated into primary care consultations to guide risk assessment also.”
By Laura Cowen
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