Routine HbA1c monitoring and cardiovascular outcomes in diabetes: Evidence from a large Spanish cohort.

Abstract

Glycated hemoglobin (HbA_1c) is a key indicator of diabetes control. However, the risk of missing HbA_1c values in clinical records is unknown. We aimed to analyze the relationship between missing HbA_1c values and the occurrence of major cardiovascular events or death from all causes. Retrospective cohort study based on a national database of primary care electronic medical records in Spain (BIFAP). We included people aged 30 years and older with an incident diagnosis of diabetes mellitus. Follow-up started on the date of diabetes diagnosis between 2005 and 2019, and ended on occurrence of composite endpoint (major cardiovascular events and/or death from all causes), or December 31st, 2019. The baseline exposure variable was HbA_1c (< 7 %, 7 %-8 %, > 8 %, missing). Cox models were fitted. Our analysis included 303,199 people with diabetes, with an average age of 62.2 years and 44.7 % were women. The mean follow-up was 5.7 years, and 10.2 % of patients had missing HbA_1c values. The cardiovascular risk was 1.18 (95 %CI: 1.14-1.22) in the HbA_1c 7 %-8 % group, 1.41 (95 %CI: 1.36-1.46) in HbA_1c > 8 %, and 2.95 (95 %CI: 2.89-3.05) in HbA_1c missing, compared with HbA_1c < 7 %. In this large cohort of people with newly diagnosed diabetes, missing HbA1c values was associated with a significantly higher risk of major cardiovascular events or death, more than double the risk observed in people with the worst glycemic control. These findings underscore the clinical importance of routinely recording and monitoring HbA1c at diagnosis, not only as a marker of metabolic control but also as a potential prognostic indicator. The lack of HbA1c may act as an indicator of suboptimal clinical follow-up.