Survival in Diabetes Tied to HbA1c Levels
HbA1c is used for diagnosing diabetes, identify pre-diabetes, and to measure how well people are doing to keep their blood glucose levels under control. A new study in the journal Lancet suggests that too tight control of blood glucose in type 2 diabetes may be as bad for survival as not controlling it.
The A1C is also called the Glycohemoglobin or Hemoglobin A1c test. It is measured in terms of percentages and reflects the average blood glucose control for the two- to three-month period before the test.
An HbA1c of 6% or less is considered normal. Persons with diabetes have been encouraged to try to keep their HbA1c level at or below 7%.
Craig J. Currie, PhD and colleagues used the UK General Practice Research Database to identify patients aged 50 years and older with type 2 diabetes between November 1986 to November 2008. They identified two groups: 27,965 patients whose treatment had been intensified from oral monotherapy to combination therapy with oral blood-glucose lowering agents, and 20,005 who had changed to regimens that included insulin.
The study looked at all-cause mortality as the primary outcome. Age, sex, smoking status, cholesterol, cardiovascular risk, and general morbidity were identified as important confounding factors. Cox survival models were used to adjust for these factors accordingly.
The study turned up a U-shaped link between all-cause mortality and glycosylated hemoglobin levels in which those at a median of 7.5% carried the lowest risk. Those with really tight glucose control (HbA1c 6.4%) were at 52% greater risk of dying from any cause during the study period. Those with poor glucose control (HbA1c 10.5%) had a 79% greater risk of dying.
The authors state “Low and high mean HbA1c values were associated with increased all-cause mortality and cardiac events. If confirmed, diabetes guidelines might need revision to include a minimum HbA1c value.”
Survival as a function of HbA1c in people with type 2 diabetes: a retrospective cohort study; The Lancet, Volume 375, Issue 9713, Pages 481 - 489, 6 February 2010, doi:10.1016/S0140-6736(09)61969-3; Dr Craig J Currie PhD, et al