Diagnosis of Type 1 Diabetes

The doctor will ask about your symptoms and health history. An exam will be done. These blood tests may be done:

Random Plasma Glucose Test

This test is taken at a random time, without regard to when food was last eaten. A sample of blood will be taken. The glucose level will be measured. A measure of 200 (mg/dl) [11.1 mmol/L] or higher is a sign of diabetes.

Two-hour Glucose Tolerance Test

This test is done after a fast of 8 to 16 hours. It is often done in the morning.

A blood sample will be taken to measure glucose levels. Then, a drink that has 75 grams of glucose will be given. Two hours later, another sample will be taken. In a person with diabetes, the glucose level will rise higher than normal and stay high for a much longer time. A measure of 200 mg/dl (7 mmol/L) or above at 2 hours is a sign of diabetes.

Hemoglobin A1c (HbA1c)

The HbA1c test measures blood glucose levels over the past 2 to 4 months. A fast is not needed before the test. A sample of blood will be taken. An HBA1c level of 6.5% or higher is a sign of diabetes.

Fasting Plasma Glucose Test

This test is done after a fast of at least 8 hours. A sample of blood will be taken to measure glucose levels. A measure of 126 milligrams per deciliter (mg/dl) (7 millimole per liter of blood [mmol/L]) or higher is a sign of diabetes.



American Diabetes Association. Standards of medical care in diabetes-2019. Diabetes Care. 2019. Jan; 42 (Suppl 1):S1-193.
Diabetes mellitus type 1. EBSCO DynaMed website. Available at: https://www.dynamed.com/condition/diabetes-mellitus-type-1-34. Updated June 28, 2019. Accessed November 22, 2019.
Type 1 diabetes. American Diabetes Association website. Available at: https://www.diabetes.org/diabetes/type-1. Accessed November 22, 2019.
Last reviewed September 2019 by EBSCO Medical Review Board James P. Cornell, MD
Last Updated: 12/8/2020

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