Diabetes mellitus

Diabetes mellitus is a chronic metabolic disorder defined by persistently elevated blood glucose (hyperglycemia) caused by inadequate insulin secretion, resistance to insulin's action, or a combination of the two. Insulin normally moves glucose from the bloodstream into cells; when that signal fails, glucose accumulates in the blood while tissues are starved of fuel.

Type 1 diabetes is autoimmune destruction of the pancreatic beta cells, producing absolute insulin deficiency. It typically presents younger, and patients require insulin for life; without it they are prone to diabetic ketoacidosis. Type 2 diabetes — far more common — combines insulin resistance with progressive beta-cell dysfunction and is strongly associated with obesity and metabolic syndrome. Gestational diabetes appears during pregnancy. Classic symptoms include polyuria, polydipsia, and polyphagia; diagnosis rests on criteria such as fasting glucose, an oral glucose tolerance test, or hemoglobin A1c, which reflects average glycemia over roughly three months.

The disease's significance lies largely in its complications. Chronic hyperglycemia damages small vessels — retinopathy, nephropathy, and neuropathy — and accelerates large-vessel atherosclerosis, raising the risk of myocardial infarction, stroke, and peripheral arterial disease. These microvascular and macrovascular sequelae make diabetes a leading cause of blindness, kidney failure, and amputation.

Diabetes mellitus is tested across health-professional exams: USMLE Step 1 emphasizes pathophysiology, diagnostic criteria, and complications; the CCMA exam covers ICD-10 coding of diabetes and the medical assistant's role in endocrine testing and care; and the NPTE-PTA tests diabetes within endocrine and metabolic system disorders relevant to rehabilitation.