The primary objectives of the study were (a) to confirm that glucose 6-phosphate dehydrogenase (G6PD) deficiency affects HbA1c values in a sample of children and adolescents with type 1 diabetes (T1D) and (b) to quantify this effect so that a correction can be applied to the HbA1c values found in current clinical practice. The gene discussed is G6PD; the disease is G6PD deficiency.