Patient Preparation Adequate meal or 75-gram glucose load two hours before two-hour postprandial glucose, as specified by the patient's physician. Patient is allowed usual meal (breakfast or lunch). Patient must complete meal within 15 to 20 minutes. Collection Collect specimen two hours from the beginning of meal. Separate serum or plasma from cells within 45 minutes of venipuncture. Gray-top tubes only, may be submitted without centrifugation. Label tube with patient's name and collection time. Only a minority of patients with diabetes mellitus have the classic symptoms of polyuria, polyphagia, polydipsia, and weight loss. The two-hour postprandial glucose is extensively used to establish the diagnosis of diabetes mellitus. It may be used along with FBS to follow patients with impaired glucose tolerance. Follow up women who had gestational diabetes, of whom most revert after delivery to normal glucose tolerance (up to half ultimately become diabetic). It is used as part of the work-up for hypertriglyceridemia, neuropathy, retinopathy, glycosuria and for certain types of renal diseases. Work-up of vulvovaginitis, blurred vision, fatigue, and some instances of urinary tract infections. Causes of postprandial hypoglycemia include alimentary type (commonly secondary to prior gastrointestinal surgery); reactive hypoglycemia without prior gastrointestinal surgery—alimentary or spontaneous, functional, idiopathic, indeterminate; some prediabetics; leucine-induced; fructose-induced; galactosemia; indeterminate group.