Diagnosis of Type 1 Diabetes

The onset of T1D is typically during childhood or puberty, and symptoms develop suddenly. Individuals with T1D can usually be recognized by the abrupt appearance of polyuria (frequent urination), polydipsia (excessive thirst), and polyphagia (excessive hunger), often triggered by physiologic stress such as an infection. These symptoms are usually accompanied by fatigue and weight loss.

The diagnosis is confirmed by a FBG ≥126 mg/dl (normal is 70–99). [Note: Fasting is defined as no caloric intake for at least 8 hours.] A FBG of 100–125 mg/dl is categorized as an impaired FBG. Individuals with impaired FBG are considered prediabetic and are at increased risk for developing T2D. Diagnosis can also be made on the basis of a nonfasting (random) blood glucose level >200 mg/dl or a glycated hemoglobin (see p. 340) concentration ≥6.5 mg/dl (normal is <5.7) in an individual with symptoms of hyperglycemia. [Note: The oral glucose tolerance test, in which blood glucose is measured 2 hours after ingestion of a solution containing 75 g of glucose, also is used but is less convenient. It is most typically used to screen pregnant women for gestational diabetes .]
When blood glucose is >180 mg/dl, the ability of renal sodium-dependent glucose transporters (SGLT) to reclaim glucose is impaired, and glucose “spills” into urine. The loss of glucose is accompanied by the loss of water, resulting in the characteristic polyuria (with dehydration) and polydipsia of diabetes.