The frequency of testing for glycated hemoglobin, HbA1c, is linked to the probability of achieving target levels in patients with sub-optimally controlled diabetes mellitus

Introduction: We previously showed, in patients with diabetes, that >50% of monitoring tests for glycated hemoglobin (HbA1c) are outside recommended intervals and that this is linked to diabetes control. Here, we examined the impact of tests/year on achievement of commonly-utilised HbA1c targets and on HbA1c changes over time. Subjects & Methods: Data on 20,690 adults with diabetes with a baseline HbA1c of >53 mmol/mol (7%) were extracted from Clinical Biochemistry Laboratory records at three UK hospitals. We examined the impact of HbA1c tests/year on: (i) probability of achieving targets of ≤53mmol/mol (7%) and ≤48mmol/mol (6.5%) in a year using multi-state modelling and (ii) changes in mean HbA1c using a linear mixed-effects model. Results: The probabilities of achieving ≤53mmol/mol (7%) and ≤48mmol/mol (6.5%) targets within 1 year were 0.20 (95% confidence interval:0.19-0.21) and 0.10 (0.09-0.10), respectively. Compared with 4 tests/year, having 1 test or >4 tests/year were associated with lower likelihoods of achieving either target; 2-3 tests/year gave similar likelihoods to 4 tests/year. Mean HbA1c levels were higher in patients who had 1 test/year compared to those with 4 tests/year (mean difference: 2.64mmol/mol [0.24%], p