Ehehalt S, Gauger N, Blumenstock G, Feldhahn L, Scheffner T, Schweizer R, Neu A for the DIARY-Group Baden-Wuerttemberg. Hemoglobin A1c is a reliable criterion for diagnosing type 1 diabetes in childhood and adolescence. Background: Little is known about the use of the hemoglobin A1C (HbA1c) test for the diagnosis of diabetes in childhood and adolescence. The aim is to investigate sensitivity and specificity of HbA1c at onset of childhood type 1 diabetes. Methods: A total of 184 children and adolescents with blood glucose levels above 200 mg/dL (11.1 mmol/L) were included: 84.8% (n = 156, mean age 9.0 yr) with new onset of type 1 diabetes, 15.2% (n = 28, mean age 6.1 yr) with transient hyperglycemia. HbA1c was measured using the Bayer DCA2000 analyzer. Results: Patients with new onset of type 1 diabetes (n = 156) had HbA1c values between 6.6% and > 14% (mean (SD) 11.4 (2.0)%; IQR, interquartile range 9.8-13.3%). All patients suffered from typical symptoms of hyperglycemia, i.e., polyuria and polydipsia. In the patient group with transient hyperglycemia (n = 28), HbA1c values were between 4.5 and 6.1% (mean (SD) 5.3 (0.4)%; IQR 5.0-5.6%). None of these patients reported typical symptoms of diabetes. All patients with HbA1c values greater than 6.35% had new onset of type 1 diabetes. Sensitivity of HbA1c at the onset of childhood type 1 diabetes was calculated to be 100%. In patients with HbA1c values less than 6.35%, the diagnosis of type 1 diabetes could be excluded. Thus, specificity of HbA1c as diagnostic criterion was 100%. Conclusions: Childhood type 1 diabetes can be diagnosed and excluded with high reliability by means of HbA1c testing. [ABSTRACT FROM AUTHOR]