Diabetes mellitus type 1 diabetes (formerly known as insulin-dependent diabetes, childhood diabetes, or juvenile-onset diabetes) is most commonly diagnosed in children and adolescents, but can occur in adults, as well.

It is characterized by β-cell destruction, which usually leads to an absolute deficiency of insulin. Most cases of type 1 diabetes are immune-mediated characterized by autoimmune destruction of the body’s β-cells in the Islets of Langerhans of the pancreas, destroying them or damaging them sufficiently to reduce insulin production. However, some forms of type 1 diabetes are characterized by loss of the body’s β-cells without evidence of autoimmunity.

Type 1 diabetes is treated with insulin injections, lifestyle adjustments, and careful monitoring of blood glucose levels using blood test kits. Insulin delivery is also available by an insulin pump, which allows the infusion of insulin 24 hours a day at preset levels, and the ability to program push doses (bolus) of insulin as needed at meal times. The treatment must be continued indefinitely. During lifetime treatment that does not impair normal activities if carried out systematically with discipline, the average glucose level for the type I diabetic patient must be at 110 mg/dl–140 mg/dl as normal, although 150 mg/dl is acceptable. Some people prefer an average above 150 mg/dl. 200–250 mg/dl is the middle-range of high blood glucose when discomfort by a need to urinate begins at 170 mg/dl, though this is dependent on the individual’s target range. 300–350 mg/dl requires a ketone analysis as well as insulin injections immediately. 350 mg/dl and above can lead to ketoacidosis if not treated with sugar-free liquids or water ideally consumed.