Longitudinal trends in HbA(1c) patterns and association with outcomes: A systematic review

BACKGROUND: This study aimed to review studies that identified patterns of longitudinal HbA(1c) trends in patients with diabetes and to summarize factors and outcomes associated with distinct trajectory patterns. METHODS: PubMed and Web of Science were systematically searched for studies examining HbA(1c) trends among patients with diabetes from database inception through September 2017. Articles were included if they met the following inclusion criteria: (a) longitudinal study of subjects with diabetes only, (b) use of serial measurements of HbA(1c), and (c) analysis of the trend of HbA(1c) using group‐based trajectory approaches. RESULTS: Twenty studies were included, 11 on type 1 diabetes and 9 on type 2 diabetes. These studies identified 2 to 6 HbA(1c) trajectory patterns. The most commonly identified patterns included stable HbA(1c) around 7.0% and at levels between 8.0% and 9.9%, which usually captured the HbA(1c) pattern among the majority of subjects in the study population. Unstable patterns identified included increasing HbA(1c) trend, decreasing HbA(1c) trend, and non‐linear patterns. These patterns were associated with differential risk of disease outcomes, over and beyond single‐point HbA(1c) measures. Age, gender, ethnicity, diabetes duration, disease management frequency, cardiovascular risk factors, insulin treatment, family environment, and psychosocial factors were the most frequently reported factors associated with membership of specific HbA(1c) pattern groups. CONCLUSION: Common patterns of longitudinal HbA(1c) trends were identified despite heterogeneity among the studies. A better understanding of what underlies these different patterns may provide opportunities to tailor therapies and care for these patients to reduce adverse outcomes.