Clinically meaningful and lasting HbA(1c) improvement rarely occurs after 5 years of type 1 diabetes: an argument for early, targeted and aggressive intervention following diagnosis

AIMS/HYPOTHESIS: Our objectives were to explore whether the phenomenon of HbA(1c) ‘tracking’ occurs in individuals with type 1 diabetes, how long after diagnosis does tracking take to stabilise, and whether there is an effect of sex and age at diagnosis on tracking. METHODS: A total of 4525 individuals diagnosed with type 1 diabetes between 1 January 1995 and 1 May 2015 were identified from The Health Improvement Network (THIN) database. Mixed models were applied to assess the variability of HbA(1c) levels over time with random effects on general practices (primary care units) and individuals within practices. RESULTS: 4525 individuals diagnosed with type 1 diabetes were identified in THIN over the study period. The greatest difference in mean HbA(1c) measurement (−7.0 [95% CI −8.0, −6.1] mmol/mol [0.6%]) was seen when comparing measurements made immediately after diagnosis (0–1 year since diagnosis) with those at 10 or more years (the reference category). The mean difference in HbA(1c) for the successive periods compared with 10 or more years after diagnosis declined and was no longer statistically significant after 5 years. In the stratified analysis using sex and age group there was considerable heterogeneity with adult onset type 1 diabetes appearing to track earlier and at a lower mean HbA(1c). CONCLUSIONS/INTERPRETATION: In individuals with type 1 diabetes, glycaemic control measured by HbA(1c) settles onto a long-term ‘track’ and this occurs on average by 5 years following diagnosis. Age at diagnosis modifies both the rate at which individuals settle into their track and the absolute HbA(1c) tracking level for the next 10 years. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s00125-018-4574-6) contains peer-reviewed but unedited supplementary material, which is available to authorised users.