According to the National Institute of Diabetes and Digestive and Kidney Diseases:
People over age 45 should be tested for prediabetes or diabetes. If the first blood glucose test is normal, they should be retested every 3 years.
People under age 45 should consider getting tested for prediabetes or diabetes if they have a body mass index (BMI) of greater than or equal to 25 kg/m2 and have 1 or more of the following risk factors:
Having a first-degree relative with diabetes (mother, father, or sibling)
Being a member of a high-risk ethnic group (African-American, Hispanic, Asian, Pacific Islander, or Native American)
Delivering a baby weighing more than 9 pounds, or having diabetes during pregnancy
Having blood pressure at or above 140/90 mm/Hg
Having abnormal blood fat levels, such as high-density lipoproteins (HDL) less than or equal to 35 mg/dL, or triglycerides greater than or equal to 250 mg/dL (mg/dL = milligrams of glucose per deciliter of blood)
Having a sedentary lifestyle
Having impaired glucose tolerance when previously tested for diabetes
Having polycystic ovarian syndrome
A diagnosis of diabetes is made when any 1 of these tests is positive. The result may be confirmed by a second positive test on a different day:
A1C greater than or equal to 6.5%
Fasting plasma glucose of greater than or equal to 126 mg/dL
Casual plasma glucose (taken at any time of the day) of greater than or equal to 200 mg/dL with the symptoms of diabetes
Oral glucose tolerance test (OGTT) value of greater than or equal to 200 mg/dL. The OGTT is obtained 2 hours after a drink containing glucose has been consumed, which occurs after fasting for at least 8 hours.
Gestational diabetes may be diagnosed with 1 of 2 approaches:
A 75-gram glucose screening test, which involves drinking a glucose drink followed by measurement of the blood sugar level after 2 hours. This test is done at 24 to 28 weeks gestation.
A 50-gram glucose screening test, which is followed by a diagnostic 100-gram glucose tolerance test in those women whose blood sugar equals or exceeds 130 mg/dL 1 hour after the initial screening test
Consult your doctor regarding your wish to be screened for gestational diabetes.