Testing blood glucose levels once a year in patients with controlled type 2 diabetes would be more suitable than testing every six months, according to a new report by the NHS.
It states that six-monthly HbA1c tests for stable type 2 diabetics, as recommended by NICE, lead to a high rate of false positives and that an annual check by GPs would provide more meaningful information on changes to HbA1c, which for most people occur quite slowly.
The NHS Diabetes report was based on statistical modelling by University of Oxford researchers which showed that for patients whose HbA1c is currently 56mmol/mol, half-yearly monitoring would pick up 405 positive tests per 1,000 patients (i.e. HbAlc > 58.5 mmol/mol). Of those, 28 per cent would be due to measurement variation and not a real increase.
Meanwhile annual monitoring among the same group of patients would pick up 479 per 1,000 patients, but only 16 per cent would be false positives.
In other groups with lower starting HbA1c readings, the researchers found that most of the positive tests seen with six-monthly tests would be false positives.
They concluded: “For many people with diabetes, six-monthly monitoring is more likely to yield a false-positive test – attributable to the within-measurement variability of HbA1c – than a true-positive test, attributable to the change over time in glycaemic control.
“Annual monitoring gives more time for a meaningful change to occur in HbA1c.”
In addition, high rates of false-positive tests mean GPs base their medication prescribing decisions largely on a “chance finding rather than a true change”, the team added.
A spokesperson for NICE said it was currently in the process of updating its guidance on type 2 diabetes management, but stressed that until the update is published, “healthcare professionals should continue to follow the recommendations set out in the current guidelines”.

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