Six-monthly monitoring of HbA1c among some patients with type 2 diabetes may be too frequent and cause unnecessary treatment changes, according to a study published by NHS Diabetes and Oxford University.
Current guidelines from the National Institute for Health and Clinical Excellence recommend six-monthly testing of HbA1c.
Researchers used study data to assess the proportion of tests that were “positive” – representing a clinically important change in observed HbA1c above 58.5 mmol/mol – compared to the proportion that would be “false positive” and the result of background variation.
They found that in patients whose HbA1c was currently 56mmol/mol, with six-monthly monitoring, the rate of positive tests would be 405 per 1,000 patients, and of these, 28% would be false positive.
With 12-monthly monitoring, the rate of positive tests would be 479 per 1,000 patients, of which 16% would be false positive.
Therefore, annual monitoring was likely to give the most accurate results, with the majority of results reflecting a true change in blood glucose control in all patients.
Lead researcher Andrew Farmer said: “False-positive tests correspond to the potential for prescribing decisions, such as a dose increase or an additional medication, being made in response to a chance finding rather than a true change.”
The study also investigated the HbA1c-lowering effects of metformin and sulfonylureas, using data from the General Practice Research Database on 100,000 people with type 2 diabetes in the UK.
The researchers found higher doses of metformin to be more effective at lowering HbA1c than lower doses, but the difference between doses was small compared to the main effect of metformin. For sulfonylureas they found no evidence for a greater effect at higher doses.
- Aronson J, et al. Optimal prescribing of glucose lowering therapy for patients with type 2 diabetes. University of Oxford 2012; Advance online publication