Regarding the debate on tight glycemic control published in the June issue of Canadian Family Physician,1 I think it might be worthwhile to look at the hemoglobin (HbA1c) levels the studies referred to actually achieved and reported, rather than what their targets were.
The achieved levels of HbA1c for the UKPDS (United Kingdom Prospective Diabetes Study) follow-up were 8.5% (conventional) versus 7.9% (intensive) in the insulin-sulphonylurea group and 8.9% (conventional) versus 8.4% (intensive) in the metformin group. There were better cardiovascular outcomes in the intensive groups, meaning those who achieved HbA1c levels of 8.4% in the metformin group or 7.9% in the insulin-sulphonylurea group. This does not mean that going below 7.9% will result in better outcomes—we simply do not know.
The HbA1c levels achieved in the ADVANCE (Action in Diabetes and Vascular Disease: Preterax and Diamicron MR Controlled Evaluation) study were 6.5% versus 7.3%. The decrease in end points was mainly driven by improvements in nephropathy.
In the VADT (Veterans Affairs Diabetes Trial), achieved HbA1c levels were 6.9% versus 8.4%. There were no differences in outcomes between the 2 groups.
In the ACCORD (Action to Control Cardiovascular Risk in Diabetes) study, levels were 6.4% versus 7.5%. There was increased mortality in the tight control group.
These studies seem to indicate that better glycemic control improves outcomes—up to a point. Where that point is is open to debate. The average HbA1c level in those studies seems to indicate that an appropriate HbA1c level is somewhere between 7% and 8%. The current average HbA1c level for my practice is 7.5%; if I systematically target patients with levels above 7% for intensification, I will drive my average down. I do not think any of the studies above tell me to do that for my practice. It seems to me that I should make a systematic effort to reduce HbA1c levels in the individual patient level to below 8%; at the practice level, the average level should be between 7% and 8%. I would have to target patients with the highest levels of HbA1c, as they will benefit the most—perhaps leaving those with levels between 7% and 8% alone—to get to results similar to those of the UKPDS.
We can now start to translate evidence from individual patient care to care of a practice population, which is a different way of looking at evidence-based medicine. I do not think clinicians should go beyond the evidence, and right now evidence does not seem to support a goal of having an overall HbA1c practice average of 7% or less. What that means in terms of individual patient goals needs to be reviewed.
We need a very clear and evidence-based definition of what “tight glycemic control” is; authors of guidelines might wish to revisit their current recommendations.
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