In the early stages of type 2 diabetes mellitus, there are no symptoms until blood glucose levels exceed the "renal threshold" and glucose appears in the urine. Patients may first present with a complication such as neuropathy or retinopathy. People in high-risk groups, who are obese, who have a family history of type 2 diabetes, or who belong to high-risk ethnic groups (e.g. African American, native American, Hispanic, Pacific Islanders) should be screened for the disorder.
When the "renal threshold" for glucose (a blood glucose level of about 180 mg/dL), is exceeded for a significant portion of the day, the patient will have the classic symptoms of diabetes: excessive urination (polyuria) with consequent thirst and need to keep drinking (polydipsia). The loss of calories, due to the urinary glucose excretion, will lead to weight loss, and often a compensatory increase in appetite (polyphagia). The weight loss primarily is due to loss of muscle mass with conversion of amino acids into glucose, and causes weakness and fatigue.
Persistent hyperglycemia can draw water into the eyes and cause visual blurring. This may persist for several weeks after correcting the hyperglycemia because of the slow diffusion of glucose out of the eyes.
Neuropathy may present with numbness, tingling or burning pain, first involving the ends of the longest nerves, i.e. those to the feet. Motor neuropathies are rare but may be acute in onset, often associated with pain, and may involve any nerve including the cranial nerves such as the oculomotor nerve.