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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) list the following test as options for diagnosis:

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 sample of your blood will be obtained 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 sample of your blood will be taken. If your HBA1c level is 6.5% or higher, this indicates a diagnosis of diabetes.

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.

Other Tests

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 low-density lipoprotein [LDL] and high-density lipoprotein [HDL] cholesterol, triglycerides)
  • Kidney function tests including serum creatinine, blood urea nitrogen (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

Revision Information

  • Arnold JG, McGowan HJ. Delay in diagnosis of diabetes mellitus due to inaccurate use of hemoglobin A1C levels. J Am Board Fam Med. 2007;20(1):93-96.

  • Diabetes causes. National Institute of Diabetes & Digestive & Kidney Diseases website. Available at: http://diabetes.niddk.nih.gov/dm/pubs/causes/index.aspx. Accessed December 31, 2012.

  • Diabetes type 1. EBSCO DynaMed website. Available at: https://dynamed.ebscohost.com/about/about-us. Updated December 28, 2012. Accessed December 31, 2012.

  • Type 1 diabetes. American Diabetes Association website. Available at: http://www.diabetes.org/diabetes-basics/type-1/?loc=DropDownDB-type1. Accessed December 31, 2012.

  • 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. Diabetes Care. 2010;33(Suppl 1):S62-S69.