Type 1 diabetes mellitus occurs when the beta cells in the pancreas are destroyed, which causes them to be unable to produce insulin. Type 2 diabetes mellitus occurs when persistent high blood glucose and insulin levels leave the tissues and organs no longer sensitized to insulin, which prevents glucose from being taken up by the cells. Type 1 diabetes is diagnosed after more than 80% of the beta cells have been destroyed, so very little insulin is being produced. However, the insulin that is produced is not faulty, there is just not enough of it. Patients with type 1 diabetes do not produce too much endogenous glucose through gluconeogenesis.