medwireNews: UK researchers suggest raising the glycated hemoglobin (HbA1c) threshold that is used to identify individuals at high risk for developing type 2 diabetes within 5 years.
Lauren Rodgers (University of Exeter) and co-workers say that reducing the number of patients designated as high risk for diabetes on the basis of an HbA1c level “would allow limited intervention opportunities to be focused on those most likely to develop [type 2 diabetes].”
They therefore believe that their study findings on thresholds “have potential implications for clinical practice.”
The authors explain in BMC Medicine that there is currently no consensus on the optimal HbA1c threshold for prediabetes, with at-risk ranges including the ADA’s 5.7–6.4% (39–47 mmol/mol) and the higher range of 6.0–6.4% (42–47 mmol/mol) as used by the International Expert Committee (IEC) and the WHO.
To investigate the impact of altering HbA1c thresholds, they collated data from 4227 participants without diabetes in the Exeter 10,000/Peninsula Research Bank population cohort, all of whom were at least 40 years old and had an HbA1c level below the diagnostic threshold for diabetes of 6.5% (48 mmol/mol) at baseline and at follow-up 4 weeks later.
Overall, 3.4% of participants developed diabetes within 5 years, with a mean time to diagnosis of 45.6 months. When compared with individuals who did not develop diabetes, those with diabetes had an average 0.15% (1.7 mmol/mol) higher HbA1c level at baseline, were 3.7 years older, and their BMI was an average 0.8 kg/m2 higher.
The absolute 5-year risk of developing diabetes in the cohort was 4.2%. Over half (56%) of the participants met the ADA threshold for high risk, but these individuals had only a “modest” 7.1% absolute risk of developing diabetes over 5 years, the researchers say, rising to 14.9% among the 22% of participants who met the IEC criteria.
However, the absolute risk of diabetes rose to 26.4% when considering only individuals with an HbA1c of 6.2–6.4% (44–47 mmol/mol), the team reports.
“Future risk of developing diabetes was very strongly related to HbA1c value within the current ‘high-risk’ categories,” write Rodgers et al, noting that people within the lower ranges of the categories had a “low” absolute risk even when clinical risk factors were present.
They calculated that changing prevention program entry criteria from a HbA1c threshold of 5.7% to 6.0% would result in a 61% reduction in the number of individuals classified as being at high risk.
This would increase the positive predictive value from 5.8% to 12.4% while having a “negligible” effect on the negative predictive value, which would decrease from 99.6% to 99.1%, the authors say.
If the threshold was further increased to 6.2%, there would be a 59% decrease in the number of people classified as high risk, an increase in the positive predictive value to 23.2% and again a small decrease in the negative predictive value to 98.5%.
The researchers caution, however, that using a 6.2% threshold would decrease sensitivity, so that 38.9% of those who developed diabetes within 5 years would be missed.
“Increasing the risk threshold markedly reduces the number of people that would be classified as high-risk and entered into prevention programmes, although this must be balanced against cases missed,” conclude Rodgers et al.
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