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Distinguishing between type 1 and type 2 diabetes

BMJ 2020; 370 doi: https://doi.org/10.1136/bmj.m2998 (Published 11 August 2020) Cite this as: BMJ 2020;370:m2998

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Re: Distinguishing between type 1 and type 2 diabetes

Dear Editor
Distinguishing between newly diagnosed type 1 and type 2 diabetes can be challenging (1). As a nation, we are becoming more obese (thus predisposing to type 2 diabetes), and we are increasingly recognising type 1 diabetes in older adults (2,3). Not infrequently this blurs the lines between type 1 and type 2 diabetes, precluding a confident categorisation of newly diagnosed diabetes. All relevant factors contributing to the risk of type 1 or type 2 diabetes should be considered. A full and detailed family history of both type 2 and type 1 diabetes and other autoimmune conditions is essential - there is a large heritable component to both which may help when the diagnosis is in balance. Ethnicity may influence and support decisions regarding diabetes classification (4). Serial c-peptide measurements may help to assess the decline of insulin secretion and thus facilitate early intervention (5). Recognising and explaining this diagnostic uncertainty to patients is also important (6).

In this case, we would argue that this man has evolving type 1 diabetes. As noted in Table 2, around 20% of adults with a new presentation of type 1 diabetes have negative autoantibodies. We find the label/diagnosis of LADA to be unhelpful and confusing to patients; we prefer to include the phrase ‘type 1 diabetes’ when describing this variant e.g. ‘slow-burning type 1 diabetes’ or ‘evolving type 1 diabetes’ (https://www.healthline.com/diabetesmine/clarifying-lada-type-1-diabetes-...).

Furthermore, in some patients with newly diagnosed type 1 diabetes (and perhaps not recognised as such), it is possible to briefly maintain blood glucose levels within target range using oral hypoglycaemic agents; however, there is a significant risk that they will progress and require insulin within weeks-to-months. This man should have diabetes education, including sick day rules, and be enabled to undertake glucose and ketone monitoring and take meaningful action based on the results.

Lastly, we suggest extreme caution in prescribing SGLT2 inhibitors for people with evolving type 1 diabetes (or LADA) because of the risk of precipitating DKA (7). We would advise discussion with Diabetes Specialists in all cases where there is uncertainty over the early diagnosis and management of diabetes.

1. Butler AE, Misselbrook D. Distinguishing between type 1 and type 2 diabetes. BMJ. 2020;370:m2998. Published 2020 Aug 11
2. Yamaguchi H, Kanadani T, Ohno M, & Shirakami A. An Ultra-Elderly Case of Acute-Onset Autoimmune Type 1 Diabetes Mellitus. J Endocrinol Metab 2016;6:71-74
3. Jones AG, Shields BM, Dennis JM, Hattersley AT, McDonald TJ, Thomas NJ. The challenge of diagnosing type 1 diabetes in older adults [published online ahead of print, 2020 Feb 11]. Diabet Med 2020;10.1111/dme
4. Misra S, Kaur A, Walkey H, et al. The Extent of Diabetes Misclassification One Year after a Diagnosis of Type 1 Diabetes: Data from the After Diabetes Diagnosis Research Support System (ADDRESS-2) Cohort. 2017, 77th Scientific Sessions of the American-Diabetes-Association, Publisher: AMER DIABETES ASSOC, Pages: A411-A412
5. Jones AG, Hattersley AT. The clinical utility of C-peptide measurement in the care of patients with diabetes. Diabet Med 2013;30(7):803-817
6. Mason C. The production and effects of uncertainty with special reference to diabetes mellitus. Soc Sci Med 1985;21:1329-1334
7. Meyer EJ, Gabb G, Jesudason D. SGLT2 Inhibitor-Associated Euglycemic Diabetic Ketoacidosis: A South Australian Clinical Case Series and Australian Spontaneous Adverse Event Notifications. Diabetes Care 2018;41:e47-e49

Competing interests: No competing interests

12 September 2020
NE Hill
Consultant Diabetes & Endocrinology
NS Oliver
Imperial College Healthcare NHS Trust
Imperial College Healthcare NHS Trsut, London