The Transatlantic HbA gap: differences in glycaemic control across the lifespan between people included in the US T1D Exchange Registry and those included in the German/Austrian DPV registry.

Aim: To compare HbA levels across the lifespan in people with type 1 diabetes in the USA with those in Germany/Austria, and to examine potential differences in HbA levels between sexes, insulin delivery methods and minority status.

Methods: Data were extracted from the US T1D Exchange Registry (n=18 381 participants from 73 sites) and from the German/Austrian Prospective Diabetes Follow-up Registry, the DPV (n=32 643 participants from 362 sites). Mean HbA was calculated for each year of age for individuals aged ≤25 years, and at 2-year age intervals for individuals aged >25 years. Curves for mean HbA by age were estimated using locally weighted scatterplot smoothing. HbA differences between registries, sexes, insulin delivery methods, and minority status were assessed by age group using multiple linear regression.

Results: In both registries, mean HbA increased by ~11 mmol/mol (1.0%) between the ages of 9 and 18 years, although at quite different absolute levels: from 66 mmol/mol (8.2%) to 77 mmol/mol (9.2%) in the T1D Exchange Registry, and from 56 mmol/mol (7.3%) to 66 mmol/mol (8.2%) in the DPV. Sex differences were observed in the DPV only. In the T1D Exchange Registry, injection users had higher mean HbA than pump users across the lifespan, whereas in the DPV higher HbA levels in injection users were observed in the age groups 6 to <12 years, 12 to <18 years, and 30 to <50 years (P < 0.001). Minority status was significantly associated with higher HbA in most age groups in both registries.

Conclusions: Significant differences in HbA were noted between the USA and Germany/Austria, with disparities more pronounced in early childhood through to young adulthood. Further studies should identify causes for these disparities.