Type 2 diabetes mellitus in adults

Type 2 diabetes mellitus is a chronic, progressive metabolic disorder characterized by hyperglycemia resulting from a combination of insulin resistance and relative insulin deficiency.

Comorbidities commonly associated with type 2 diabetes include obesity, hypertension, heart failure (HF) and sleep disorders, as well as other conditions associated with macrovascular complications (coronary artery, cerebrovascular, and peripheral vascular disease) and microvascular complications (nephropathy, retinopathy, and neuropathy).

Type 2 diabetes therapy for all patients hinges around a personalized self-management program, usually developed with the patient and their care team made up of physicians, diabetes education nurses, and/or nutritionists.

Glycemic goals and treatment choices should be individualized. Due to the progressive nature of the condition, escalation/combination therapy is often required.

Lifestyle changes plus metformin are initial antihyperglycemic therapy for most patients, although for individuals with atherosclerotic cardiovascular disease (ASCVD) or at high risk of ASCVD, HF, or chronic kidney disease, sodium-glucose cotransporter-2 (SGLT2) inhibitors or glucagon-like peptide-1 (GLP-1) receptor agonists should be prioritized for their cardiorenal protective effects. For patients with overweight or obesity, weight management should be considered as a therapeutic target in addition to glycemia, and drugs chosen that both promote weight loss and lower glucose. This particularly includes GLP-1 receptor agonists and dual glucose-dependent insulinotropic polypeptide (GIP)/GLP-1 receptor agonists.

In addition to antihyperglycemic therapy, management of blood pressure and lipids, smoking cessation, and antiplatelet therapy (where indicated) are essential to reduce the risk of macrovascular and microvascular complications.

Type 2 diabetes mellitus is a progressive disorder defined by deficits in insulin secretion and action that lead to abnormal glucose metabolism and related metabolic derangements.[1]Meigs JB, Muller DC, Nathan DM, et al. The natural history of progression from normal glucose tolerance to type 2 diabetes in the Baltimore Longitudinal Study of Aging. Diabetes. 2003 Jun;52(6):1475-84. https://diabetes.diabetesjournals.org/content/52/6/1475.full http://www.ncbi.nlm.nih.gov/pubmed/12765960?tool=bestpractice.com Although the etiologies of type 1 and type 2 diabetes differ dramatically, both lead to hyperglycemic states, and both share common macrovascular (coronary heart, cerebrovascular, and peripheral vascular disease) and microvascular (retinopathy, nephropathy, and neuropathy) complications.

Type 2 diabetes is most often diagnosed following routine screening. It is preceded by a state of prediabetes, which is defined by a single fasting plasma glucose (FPG) of 100-125 mg/dL (5.6 to 6.9 mmol/L), or plasma glucose of 140-199 mg/dL (7.8 to 11.0 mmol/L) 2 hours after 75 g oral glucose, or a hemoglobin A1c (HbA1c) of 5.7% to 6.4% (39-47 mmol/mol) in the absence of diabetes.[2]American Diabetes Association. Standards of care in diabetes - 2025. Diabetes Care. 2025 Jan 1;48(suppl 1):S1-336. https://diabetesjournals.org/care/issue/48/Supplement_1 In the absence of unequivocal hyperglycemia, diabetes diagnosis is based on two confirmed values of: FPG ≥126 mg/dL (≥7.0 mmol/L), plasma glucose ≥200 mg/dL (≥11.1 mmol/L) 2 hours after 75 g oral glucose, or HbA1c of ≥6.5% (≥48 mmol/mol).[2]American Diabetes Association. Standards of care in diabetes - 2025. Diabetes Care. 2025 Jan 1;48(suppl 1):S1-336. https://diabetesjournals.org/care/issue/48/Supplement_1 Alternatively, diabetes can be diagnosed with a single random plasma glucose of ≥200 mg/dL (≥11.1 mmol/L) plus symptoms of hyperglycemia or hyperglycemic crisis.[2]American Diabetes Association. Standards of care in diabetes - 2025. Diabetes Care. 2025 Jan 1;48(suppl 1):S1-336. https://diabetesjournals.org/care/issue/48/Supplement_1 A single blood sample is sufficient to establish a diabetes diagnosis if assays of both HbA1c and FPG meet criteria for diabetes diagnosis.[2]American Diabetes Association. Standards of care in diabetes - 2025. Diabetes Care. 2025 Jan 1;48(suppl 1):S1-336. https://diabetesjournals.org/care/issue/48/Supplement_1

Diabetes management, once centered mainly on glycemia, has shifted towards a disease-modifying approach. See Diabetic kidney disease and Diabetic cardiovascular disease for specifics of glycemic management in the setting of these comorbidities.