MODEL RELEASED. Insulin pen. Nurse preparing a flexpen, a pre-filled insulin pen used by diabetics, for use. She is turning the dial to set the correct dose of insulin for the patient. Diabetes is a metabolic disorder in which either the production of the hormone insulin, which regulates blood glucose levels, is reduced, or the sensitivity of body tissues to insulin is reduced. This causes unused sugars to accumulate in the blood and urine. Blood glucose levels must be carefully monitored. Treatment is with a strict diet and daily insulin injections to maintain the correct blood-sugar balance. Once all the insulin in the cartridge has been used, the device can be thrown away.