Random (non-fasting) blood glucose level -- diabetes is suspected if higher than 200 mg/dL and accompanied by the classic symptoms of increased thirst, urination, and fatigue (this test must be confirmed with a fasting blood glucose test).
Oral glucose tolerance test -- diabetes is diagnosed if glucose level is higher than 200 mg/dL after 2 hours.
References:
Rao G. Insulin resistance syndrome. Am Fam Physician. 2001 Mar 15;63(6):1159-63, 1165-6.