TY - JOUR T1 - Importance of applying treatment data to ascertain type 1 diabetes cases in health registries JF - BMJ Open Diabetes Research & Care JO - BMJ Open Diab Res Care DO - 10.1136/bmjdrc-2021-002280 VL - 9 IS - 1 SP - e002280 AU - Mitra Mosslemi AU - Nathan D Wong Y1 - 2021/04/01 UR - http://drc.bmj.com/content/9/1/e002280.abstract N2 - We read with great interest the article by Casagrande and colleagues concerning the comparison of the survey-based algorithms to ascertain type 1 diabetes (T1D) in the National Health and Nutrition Examination Survey (NHANES) and the National Health Interview Survey (NHIS).1 Emphasizing the recent updates about the distribution of age at T1D onset is a great point in their work; however, an evidence-based comparison between the algorithms’ accuracy would have been useful to the reader.We had previously developed a treatment-based algorithm for identifying diabetes type in the NHANES after evaluating the magnitude of misclassification for each of the potential criteria for the classification from the epidemiologic evidence.2 We excluded age at the diabetes diagnosis criterion because of its high rate of misclassification in the ascertainment of T1D.3 4 Instead, we used ‘No use of oral hypoglycemic medication’, ‘Current insulin use’, and ‘Started taking insulin within a year after the diagnosis’ criteria.2 We agree with Casagrande et al that ‘No use of oral hypoglycemic medication’ alone is not enough … ER -