Prevalence of Abnormal Hemoglobin A1c Values in Single Ventricle Patients Following Fontan Palliation.

Fontan palliation has improved survival in single ventricle patients. However, Fontan patients are subject to long-term morbidity. A few previous studies suggest Fontan patients have an increased risk of abnormal glucose metabolism without a clear mechanism. We aim to evaluate the prevalence and severity of abnormal hemoglobin A1c (HbA1c) values in Fontan patients and identify associated factors. Single-center retrospective cross-sectional cohort study including Fontan patients and documented HbA1c testing. Univariate demographic, anthropometric, and laboratory variable comparisons were completed and a stepwise selection multivariate regression model was attempted. The study included 414 Fontan patients, median age of 19 years (range 3-59 years). Of these, 190 patients (60.5% male) had at least one HbA1c. Abnormal HbA1c (> 5.6%) was found in 36% (n = 70) and diabetic-range HbA1c (≥ 6.5%) in 4.7% (n = 9). Factors associated with abnormal HbA1c included non-white race (63% vs 45%, p = 0.018), female sex (49% vs 34%, p = 0.050), elevated adult BMI [29.6 (± 8.4) vs 24.8 (± 4.8), p =  < 0.0001], elevated blood glucose [108.7 (± 47.3) vs 91.1 (± 17.9), p =  < 0.0001], and elevated triglycerides [101.5 (± 52.9) vs 84.1 (± 50.9), p = 0.029]. There were no significant differences found between the two HbA1c groups regarding cardiac diagnoses or surgical factors including type of stage 1 procedure, type of stage 3 procedure, or fenestration of Fontan. Patient age at time of initial Fontan procedure and time since initial Fontan showed no association with abnormal glucose metabolism. Obesity (BMI z-score ≥ 1.6 in children and BMI ≥ 30 in adults) was correlated with abnormal HbA1c (p = 0.008, 95%CI 0.069-0.45). There is a high prevalence of elevated HbA1c values in Fontan patients with modifiable associated factors, such as obesity and hypertriglyceridemia. Further investigation is needed to identify additional associated factors for abnormal glucose metabolism and determine its clinical significance. Lastly, we propose a new management protocol to screen for abnormal glucose metabolism.