What happens with a lack of insulin?

In diabetic cats the pancreas can no longer produce enough insulin. Without insulin, glucose is no longer able to leave the bloodstream to be used as energy by the body's cells. Hence the glucose in the blood will rise to an abnormally high level. The level will become so high that glucose overflows into the urine and your cat's urine will contain glucose.

The body's cells cannot utilise the glucose they depend upon for energy. In order to compensate for this, other ‘abnormal' energy producing processes start up which do not depend on glucose (such as fat break-down). Unfortunately, these processes eventually create toxic by-products that can make your cat very sick.