Diabetes Type 1 Diagnosis: What Tests Will the Doctor Order to Determine the Type of Diabetes You Have?

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About Type 1 Diabetes

Type 1 diabetes is an autoimmune disease in which the immune system attacks and destroys the β-cells of the pancreas. Patients with a diabetes type 1 diagnosis will often display destruction of up to 90 percent of these cells. The β-cells are the cells responsible for the production and secretion of insulin in response to elevated levels of blood glucose following a meal. In healthy individuals, insulin is secreted and helps glucose exit the bloodstream and enter metabolically active tissues for energy. Type 1 diabetics do not produce enough insulin due to the destruction of the insulin-secreting β-cells. They require regular doses of insulin to manage their blood glucose levels and prevent the long-term complications associated with diabetes.

Diabetes type 1 diagnosis occurs through blood screenings. The first test detects the condition of diabetes mellitus. Later blood tests are performed in order to determine the specific type of diabetes from which a patient is suffering.

Glycated Hemoglobin (A1c) Test

Hemoglobin (Hb) is the compound in the red blood cells that binds oxygen and carries it through the bloodstream. The life-span of a hemoglobin molecule is about 120 days. In patients who exhibit long-term high blood glucose levels (hyperglycemia), the hemoglobin binds some of this glucose and is said to be glycated; following glycosylation, the hemoglobin remains that way until it reaches the end of its life-span.

A blood test is performed, and the sample is sent to a laboratory. The test results come back as a percentage called the estimated average glucose (eAG). The eAG is determination of how much blood sugar the hemoglobin has been exposed to during its life-span; this displays the average level of blood glucose over a one to three month period. Healthy individuals usually display between four and six percent A1c. Diabetic patients will display above 6.5 percent.

This test should not be used to diagnose diabetes in pregnant women, patients with severe bleeding or a recent blood transfusion, patients with kidney or liver disease and patients with blood disorders.

Random Blood Sugar

At any time, a physician may order a blood sugar test. Blood sugar tests are determined by the concentration of glucose in the blood as milligrams per deciliter (mg/dL). A random blood sugar measurement of greater than 200 mg/dL is indicative of diabetes, especially when coupled with other symptoms of the disease.

Fasting Blood Glucose

If diabetes is suspected, your physician may order a fasting blood glucose test. You will be required to fast for several hours prior to the test. A blood sample will be drawn and the blood glucose measured. Measurements over 126 mg/dL on two separate occasions indicates diabetes.

Oral Glucose Tolerance Test

Your physician may order an oral glucose tolerance test, usually at the same time as a fasting blood glucose. It will be the first part of the test and then the patient will drink a glucose solution. Blood glucose measurements will be taken at predetermined intervals. Two measurements at the two-hour mark of over 200 mg/dL indicates diabetes.

Differential Diagnosis

After a diagnosis of diabetes mellitus, the physician must determine which type of diabetes is affecting his or her patient. In patients with type 1 diabetes, one or more of several types of autoantibodies will be present in blood samples. The presence of these antibodies provides a differential diagnosis of type 1 versus type 2 diabetes.

Another criteria for diabetes type 1 diagnosis is the presence of ketones in the patient’s urine (ketonuria). Ketones are waste products from the use of fats as fuel, as opposed to glucose, which build up in the bloodstream; some are expelled in the urine. These compounds are toxic in high amounts and result in the development of a dangerous condition called ketoacidosis.


Mayo Clinic: Type 1 Diabetes: Tests and Diagnosis

National Diabetes Information Clearinghouse: Diagnosis of Diabetes

MedlinePlus Medical Encyclopedia: Type 1 Diabetes

University of Maryland Medical Center: Diabetes-Type 1-Diagnosis

Lab Tests Online: A1c and eAG: The Test

Lab Tests Online: Glucose Tests: The Tests

Lab Tests Online: Diabetes-related Autoantibodies: The Test