How are type 1 and type 2 diabetes mellitus (DM) differentiated?

Updated: Jul 28, 2020
  • Author: Romesh Khardori, MD, PhD, FACP; Chief Editor: George T Griffing, MD  more...
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Answer

Type 1 versus type 2 diabetes

Determining whether a patient has type 1 or type 2 DM is an important diagnostic and therapeutic concern because patients with type 1 DM depend on continuous exogenous insulin for survival. A patient whose diabetes is controlled with diet or an oral antidiabetic agent clearly has type 2 DM. A lean patient who has had diabetes since childhood, who has always been dependent on insulin, or who has a history of diabetic ketoacidosis (DKA) almost certainly has type 1 DM.

Distinguishing the type of diabetes can be difficult in (1) patients who are treated with insulin and who are younger but clinically appear to have type 2 DM and (2) older patients with late-onset diabetes who nonetheless take insulin and seem to share characteristics of patients with type 1 DM. (This latter group is now said to have latent autoimmune diabetes of the adult [LADA].) It should be noted that for many patients, it will not be possible to fully distinguish type 1 DM from type 2.

When in doubt, treat the patient with insulin and close monitoring of glucose levels. It is not unusual for adolescents or young adults, particularly Hispanic or African-American patients, to present with DKA and subsequently be found to have type 2 DM.


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