The frequency of testing for glycated haemoglobin, HbA1c, is linked to the probability of achieving target levels in patients with suboptimally controlled diabetes mellitus.

Abstract

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<0.001).

Conclusions:
We showed that =80% of patients with sub-optimal control are not achieving commonly recommended HbA1c targets within 1 year, highlighting the major challenge facing healthcare services. We also demonstrated that, while appropriate monitoring frequency is important, 6-monthly testing is as effective as quarterly testing, supporting international recommendations. We suggest that the importance HbA1c monitoring frequency is being insufficiently recognised in diabetes management.