Diagnosis of Type 1 Diabetes
The doctor will ask about your symptoms and medical and family history. A physical exam will be done. The doctor will also do a few tests. There are four main tests used to diagnose diabetes. The American Diabetes Association (ADA) recommends the following tests for diagnosis:
Fasting Plasma Glucose Test
You will need to eat nothing for at least eight hours before the test. A sample of your blood will be taken. The blood glucose level will be measured. A measure of 126 milligrams per deciliter (mg/dl) (7 millimole per liter of blood [ mmol/L]) or higher on two separate occasions indicates a diagnosis of diabetes.
Symptoms and Results of Random Plasma Glucose Test
Symptoms typical of diabetes include excessive thirst and hunger, frequent urination, and weight loss. Your doctor will make the diagnosis based on your symptoms and the results of the random plasma glucose test. This test is taken any time of day, without regard to when you have last eaten. A sample of your blood will be taken. The blood glucose level will be measured. A measure of 200 (mg/dl) [11.1 mmol/L] or higher indicates the presence of diabetes.
Two-hour Glucose Tolerance Test
This starts with a three-day intake of a diet consisting of at least 150 grams of carbohydrates. You will then be asked to fast overnight (between 8-16 hours). The test is generally done in the morning, in your doctor's office.
A blood sample will be obtained from you to measure blood sugar. Then, you will consume a drink that contains 75 grams of glucose dissolved in water. Two hours later, another blood sample will be obtained to measure blood sugar. If you have diabetes, your blood sugar level will rise higher than normal and remain high for a much longer time than is normal. A measure of 200 mg/dl (7 mmol/L) or above at two hours is considered a positive test.
Hemoglobin A1c (HbA1c)
The HbA1c test is a good indicator of your average blood sugar levels over the previous 2-4 months. This test usually does not require any dietary restrictions. A blood sample will be taken. If your HBA1c level is 6.5% or higher, this indicates a diagnosis of diabetes.
After the diagnosis of diabetes is confirmed, your doctor will most likely order the following tests:
- Urine microalbumin—to see if there is any damage to your kidneys by measuring protein in your urine
- Thyroid function tests
- Blood lipids (cholesterol) levels (total, LDL, and HDL cholesterol, triglycerides)
- Kidney function tests including serum creatinine, BUN, and potassium
Less commonly ordered tests may include:
- Glutamic acid decarboxylase (GAD) antibodies
- Plasma insulin levels
- Islet cell antibodies
- Plasma C-peptide
- Insulin antibodies
American Diabetes Association website. Available at: http://www.diabetes.org/home.jsp .
Diabetes type 1. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed/what.php. Updated January 2010. Accessed February 23, 2010.
Diagnosis and classification of diabetes mellitus. Daibetes Care . 2005;28(Suppl 1):S37-42.
Diagnosis of type 2 diabetes. EBSCO Health Library website. Available at: http://www.ebscohost.com/thisTopic.php?marketID=15topicID=81. Updated February 2010. Accessed February 23, 2010.
National Institute of Diabetes & Digestive & Kidney Diseases website. Available at: http://www.niddk.nih.gov/.
Last reviewed December 2009 by
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