Disparities in Hemoglobin A1c Testing During the Transition to Adulthood and Association With Diabetes Outcomes in Youth-Onset Type 1 and Type 2 Diabetes: The SEARCH for Diabetes in Youth Study

OBJECTIVE To identify correlates of hemoglobin A1c (HbA1c) testing frequency and associations with HbA1c levels and microvascular complications in youth-onset diabetes. RESEARCH DESIGN AND METHODS The SEARCH for Diabetes in Youth study collected data from individuals diagnosed with diabetes before age 20 at 8 years (n = 1,885 type 1, n = 230 type 2) and 13 years (n = 649 type 1, n = 84 type 2) diabetes duration. We identified correlates of reporting ≥3 HbA1c tests/year using logistic regression. We examined associations of HbA1c testing with HbA1c levels and microvascular complications (retinopathy, neuropathy, or nephropathy) using sequentially adjusted linear and logistic regression. RESULTS For type 1 diabetes, odds of reporting ≥3 HbA1c tests/year at 8 and 13 years diabetes duration decreased with older age at diagnosis (odds ratio [OR] 0.91 [95% CI 0.88–0.95]), longer duration of diabetes (OR 0.90 [0.82–0.99]), not having a personal doctor (OR 0.44 [0.30–0.65]), and lapses in health insurance (OR 0.51 [0.27–0.96]). HbA1c testing ≥3 times/year over time was associated with lower HbA1c levels (OR −0.36% [−0.65 to −0.06]) and lower odds of microvascular complications (OR 0.64 [0.43–0.97]) at 13 years' duration, but associations were attenuated after adjustment for HbA1c testing correlates (OR −0.17 [−0.46 to 0.13] and 0.70 [0.46–1.07], respectively). For type 2 diabetes, not seeing an endocrinologist decreased the odds of reporting ≥3 HbA1c tests/year over time (OR 0.19 [0.06–0.63]), but HbA1c testing frequency was not associated with HbA1c levels or microvascular complications. CONCLUSIONS We observed disparities in HbA1c testing frequency predominately by health care–related factors, which were associated with diabetes outcomes in type 1 diabetes.