Variability in test interval is linked to glycated haemoglobin (HbA1c) trajectory over time in people with diabetes

ABSTRACT

Introduction: Frequency of HbA1c testing links to outcome in terms of HbA1c control in diabetes. The influence of the variability of test-retest interval on HbA1c change needs to be determined. Methods: HbA1c results were collected from laboratory records on 3,872 people HbA1c results at baseline and 5 years( ± 3 months) later with at least 6-tests during this period. We calculated the standard deviation (SD) of test interval for each individual. We then examined the link between deciles of SD of test interval/HbA1c level, stratified by baseline HbA1c. Results: In general, less variability in testing frequency = more consistent monitoring associated with better diabetes control over a 5-year period. This was most evident with moderately raised baseline HbA1c levels(54-75mmol/ mol[7.0-9.0%]). For example, in those with a starting HbA1c of 54-58mmol/ mol[7.0-7.5%], the lowest SDdecile associated with little change in HbA1c over 5 years, while for the highest SDdecile, HbA1c rose by 4-6mmol/ mol[0.4-0.6%], (p < 0.0001, standard beta 0.09-0.10). Multivariate analysis showed that the association was independent of age/sex/hospital site. Stratification by age suggested that the effect was most pronounced in those aged <65 years with baseline HbA1c 54-58mmol/ mol[7.0- 7.5%] (p < 0.0001, standard beta = 0.12). We also observed a 6.7-fold variation in the proportion of people in the top three SDdeciles across general practices. Conclusion/Interpretation: These findings indicate that consistency of testing interval, not just numbers of tests/year, is important in maintaining diabetes control, especially in those with moderately raised HbA1c. This suggests the need for developing systems to improve the regularity of HbA1c testing, especially given the recent impact of covid-19 on diabetes monitoring.