成人第1 型糖尿病臨床特徵較不典型，誤診或延遲診斷的情況，並不少見。本文提出成 人發病之糖尿病三例，包括潛伏型成人自體免疫糖尿病(latent autoimmune diabetes in adults; LADA)，猛暴性，非自體免疫第1 型糖尿病(fulminant, non-autoimmune type 1 diabetes)，易 酮病型第2 型糖尿病(ketosis-prone type 2 diabetes)。我們建議，除了使用LADA 臨床風險分 數(LADA clinical risk score) 外，若有早期胰島衰竭的現象，如「發病到需胰島素治療時間」 (time to insulin) 小於3 年至6 年及消瘦，就應該進行胰島自體抗體及胰島功能測試，以便 及時診斷LADA。所有以酮酸中毒(DKA) 為初始表現的糖尿病人，應儘快檢驗糖化血色素 (glycated hemoglobin; HbA1c)，若HbA1c 值很接近正常，就有可能是猛暴性第1 型糖尿病； 需例行性測試胰島自體抗體及胰島功能，對於早期確認第1 型或2 型糖尿病很有幫助。胰島 自體抗體以GADA (glutamic acid decarboxylase antibody) 為首選，若為陰性，可再測IA-2A (insulinoma antigen-2 autoantibody)、IAA (insulin autoantibody) 或ZnT8A (zinc transporter 8 autoantibody) 等抗體，以提升其敏感度。胰島功能可以使用簡便的隨機採血檢驗非空腹C- 胜 肽(non-fasting random C-peptide)，或標準的昇糖素刺激試驗(glucagon stimulation test)。有些 LADA 可能需要在糖尿病發病後3 至5 年才能從C- 胜肽濃度鑑別診斷，因此追蹤及重覆測試 很重要。

Adult-onset type 1 diabetes have more atypical clinical features than childhood-onset type 1 diabetes. Not uncommonly, it is either misclassified as type 2 diabetes or diagnosed as type 1 diabetes only after some delay. We reported three cases of adult-onset diabetes, diagnosed respectively as LADA (latent autoimmune diabetes in adults), fulminant non-autoimmune type 1 diabetes, and ketosis-prone type 2 diabetes. We recommend that all adult diabetic patients should undergo assessment of islet cell autoimmunity and β cell function in addition to calculating the LADA clinical risk score if they exhibit signs indicating premature β cell failure, such as “time to insulin requirement less than 3 to 6 years” or unintended weight loss. Those with ketoacidosis as initial manifestation of diabetes should have HbA1c (glycated hemoglobin) measured as soon as possible to exclude fulminant type 1 diabetes, which is characterized by low, even near-normal, HbA1c levels. These patients also need routine measurement of islet autoantibodies and C-peptide levels, which are critical for early differentiation of type 1 from type 2 diabetes. The best single autoantibody screening test for autoimmune diabetes is GADA (glutamic acid decarboxylase antibody). If GADA is negative, IA-2A (insulinoma antigen-2 autoantibody), IAA (insulin autoantibody) or ZnT8A (zinc transporter 8 autoantibody) can be measured additionally to increase diagnostic sensitivity. A non-fasting random blood C-peptide level is a practical test to assess β cell function, which may also be formally assessed by a glucagon stimulation test. Because some LADA patients may still maintain insulin secretion for 3 to 5 years, repeat measurements of C-peptide and close follow-up are important during this period. (J Intern Med Taiwan 2016; 27: 274-279)