Diabetes mellitus type 1 (Type 1 diabetes, T1D, T1DM, IDDM, juvenile diabetes) is a form of diabetes mellitus. Type 1 diabetes is an autoimmune disease that results in destruction of insulin-producing beta cells of the pancreas. Lack of insulin causes an increase of fasting blood glucose (around 70-120 mg/dL in nondiabetic people) that begins to appear in the urine above the renal threshold (about 190-200 mg/dl in most people), thus connecting to the symptom by which the disease was identified in antiquity, sweet urine. Glycosuria or glucose in the urine causes the patients to urinate more frequently, and drink more than normal (polydipsia). Classically, these were the characteristic symptoms which prompted discovery of the disease.
Type 1 is lethal unless treated with exogenous insulin. Injection is the traditional and still most common method for administering insulin; jet injection, indwelling catheters, and inhaled insulin has also been available at various times, and there are several experimental methods as well. All replace the missing hormone formerly produced by the now non-functional beta cells in the pancreas. In recent years, pancreas transplants have also been used to treat type 1 diabetes. Islet cell transplant is also being investigated and has been achieved in mice and rats, and in experimental trials in humans as well. Use of stem cells to produce a new population of functioning beta cells seems to be a future possibility, but has yet to be demonstrated even in laboratories as of 2008.
Type 1 diabetes (formerly known as "childhood", "juvenile" or "insulin-dependent" diabetes) is not exclusively a childhood problem; the adult incidence of type 1 is noteworthy—many adults who contract type 1 diabetes are misdiagnosed with type 2 due to confusion on this point.
There is currently no clinically useful preventive measure against developing type 1 diabetes, though a vaccine has been proposed and anti-antibody approaches are also being tested. Most people who develop type 1 were otherwise healthy and of a healthy weight on onset, but they can lose weight quickly and dangerously, if not promptly diagnosed. Although the cause of type 1 diabetes is still not fully understood, the immune system damage is characteristic of type 1.
The most definite laboratory test to distinguish type 1 from type 2 diabetes is the C-peptide assay, which is a measure of endogenous insulin production since external insulin has not (to date) included C-peptide. The presence of anti-islet antibodies (to Glutamic Acid Decarboxylase, Insulinoma Associated Peptide-2 or insulin), or lack of insulin resistance, determined by a glucose tolerance test, would also be suggestive of type 1. Many type 2 diabetics continue to produce insulin internally, and all have some degree of insulin resistance.
Testing for GAD 65 antibodies has been proposed as an improved test for differentiating between type 1 and type 2 diabetes as it appears that the immune system malfunction is connected with their presence.