Glycated Hemoglobin

Importance: Type 2 diabetes involves progressive loss of insulin secretion from pancreatic β cells in the setting of insulin resistance and manifests clinically as hyperglycemia. Type 2 diabetes accounts for 90% to 95% of all cases of diabetes globally, with estimates ranging from 589 million to 828 million people worldwide. In the US, type 2 diabetes affects approximately 1 in 6 adults.

Observations: Risk factors for type 2 diabetes include older age, family history, overweight or obesity, physical inactivity, gestational diabetes, Hispanic ethnicity, and American Indian or Alaska Native, Asian, or Black race. Diabetes is diagnosed if fasting plasma glucose is greater than or equal to 126 mg/dL, hemoglobin A1C is greater than or equal to 6.5%, or 2-hour glucose during 75-g oral glucose tolerance testing is greater than or equal to 200 mg/dL. Approximately one-third of adults with type 2 diabetes have cardiovascular disease and 10.1% have severe vision difficulty or blindness. The prevalence of type 2 diabetes is 39.2% among patients with kidney failure. Although weight management is an important component of treatment for type 2 diabetes, no specific diet has been proven to be most effective for improving health outcomes. Physical activity can reduce hemoglobin A1C by 0.4% to 1.0% and improve cardiovascular risk factors (ie, hypertension and dyslipidemia). Randomized clinical trials have reported absolute reductions in microvascular disease (3.5%), such as retinopathy and nephropathy, myocardial infarction (3.3%-6.2%), and mortality (2.7%-4.9%), with intensive glucose-lowering strategies (hemoglobin A1C <7%) vs conventional treatment 2 decades after trial completion. First-line medications for type 2 diabetes include metformin and, in patients with cardiovascular or kidney comorbidities or at high cardiovascular risk, glucagon-like peptide-1 receptor agonists (GLP-1RAs) or sodium-glucose cotransporter 2 inhibitors (SGLT2is). Common add-on medications include dual glucose-dependent insulinotropic polypeptide (GIP)/GLP-1RAs, dipeptidyl peptidase-4 inhibitors, sulfonylureas, and thiazolidinediones. Approximately one-third of patients with type 2 diabetes require treatment with insulin during their lifetime. Several randomized clinical trials have demonstrated benefits of specific SGLT2i and GLP-1RA medications compared with placebo for atherosclerotic cardiovascular disease (12%-26% risk reduction), heart failure (18%-25% risk reduction), and kidney disease (24%-39% risk reduction) over 2 to 5 years. Most trial participants with type 2 diabetes were taking metformin. High-potency GLP-1RA and dual GIP/GLP-1RA medications result in weight loss of greater than 5% in most individuals with type 2 diabetes, and weight loss may exceed 10%.

Conclusions: Type 2 diabetes affects up to 14% of the global population and is associated with preventable long-term complications, such as cardiovascular disease, kidney failure, vision loss, and increased mortality. In addition to lifestyle modifications including diet, exercise, and weight management, metformin is generally first-line therapy for attainment of hemoglobin A1C targets. For individuals with type 2 diabetes and cardiovascular or kidney disease or at high cardiovascular risk, guidelines recommend early treatment with SGLT2i and/or GLP-1RA medications.