A non-diabetic subject will very rarely have a blood glucose level that exceeds 8 mmol/L. Above this level the glucose will leak into the urine, and the classic symptoms of increased urine production and thirst will ensue in both forms of diabetes.
Type II diabetes often has a 'subclinical' phase where the blood glucose levels oscillate between 8 and 14 mmol/L. This phase is dangerous, as it is in this phase that structural damage takes place. Often the presenting features of diabetes are the irreversible structural damage to the retina, kidneys, the nervous system and the heart.
Type I diabetes is also associated with dehydration. The major symptoms of type I diabetes are associated with the acute complications such as ketoacidosis (see section on complications of diabetes). Patients will often complain before a ketoacidotic attack of the following symptoms:
1) Visual blurring
2) Muscle cramps
3) General tiredness