A chronic disorder, Type 1 diabetes results from a complete or partial lack of insulin. Without insulin, glucose can’t enter the cells. Thus, the cells starve while high levels of glucose remain in the bloodstream. The body, sensing a lack of glucose in the cells, tries to increase its availability by breaking down fat and protein sources and glycogen stores to produce glucose. In another attempt to compensate, the body secretes counterregulatory hormones (glucagon, epinephrine, growth hormone, and cortisol) to increase blood glucose levels. But without insulin, these increases in glucose only contribute further to hyperglycemia.When the amount of glucose filtered by the kidneys surpasses the amount the kidneys can reabsorb, glucose appears in the urine. The glucose acts as an osmotic diuretic, causing the patient to produce increased amounts of urine. Elevated blood glucose levels also increase the osmotic pull of the blood, which causes water to move from the cells in the tissues into the bloodstream. This intracellular dehydration, along with the dehydration caused by increased urination, produces excessive thirst. Because the cells lack the glucose they need for energy, the person is continually hungry.

As the person burns fat and proteins for energy, fatigue and weight loss result. As body fats continue to break down, toxic levels of ketones are produced. Ketones can’t be used efficiently as energy, and as they accumulate in the blood, the pH drops, and metabolic acidosis develops. As the kidneys filter ketones, ketonuria develops. Insulin replacement is necessary to prevent DKA. The signs and symptoms of DKA include nausea, vomiting, electrolyte imbalances, a fruity breath odor, weight loss, and muscle wasting. Without treatment, DKA can progress to coma and death.

After being diagnosed with Type 1 diabetes, many patients experience a remission during which little or no insulin therapy is needed to control blood glucose levels. This honeymoon period can last up to a year, but once it ends, blood glucose levels rise, and insulin requirements increase.

Even when the disease is treated with exogenous insulin, it progresses, producing long-term complications. These complications can be classified as microvascular, macrovascular, and neuropathic. Microvascular complications include retinopathy, which can lead to blindness, and nephropathy, which can lead to renal failure. Macrovascular complications include coronary artery disease, cerebrovascular disease, and peripheral vascular disease. Neuropathies can lead to conditions including impotence and a loss of sensation in the arms and legs. Among patients with Type 1 diabetes, renal disease is the most common cause of death, followed by cardiovascular disease.