Clinical Chemistry - Glucose Tolerance Test


This module includes video/animation, text, and self-assessment concerning the conduct and application of the GTT.


The diagnosis of diabetes must be made with care since it has far-reaching medical and social consequences. The World Health Organization has established guidelines for the diagnosis of Diabetes Mellitus on the basis of blood glucose results and the response to a glucose load. Response to an oral glucose load has been standardized as a timed diagnostic procedure and is referred to as the Oral Glucose Tolerance Test (or OGTT).

Author(s): Francis A. YeboahView Details of Author
Year: 2009
Keywords: glusoce tolerance test, glusoce test, gtt,
Licensing Condition:

cc-by-nc© 2009, KNUST

Unless otherwise noted, the content of this programme is licensed under the terms of a Creative Commons Attribution-NonCommercial 3.0 Unported License.



Any medical information in this material is intended to inform and to educate and is not a tool for self-diagnosis or a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional. You should speak to your physician or make an appointment to be seen if you have questions or concerns about this information or your medical condition.




Procedures in Clinical Chemistry

This site is intended as a compendium of programmes concerning procedures in clinical chemistry. Currently, the programme includes only a module on Glucose Tolerance Testing (GTT). This module includes video/animation, text, and self-assessment concerning the conduct and application of the GTT.




To understand the purpose of glucose tolerance test

To learn how to perform the glucose tolerance test and observe results

To be able to identify abnomalities in series of tests


Lesson Content


Performing the Oral Glucose Tolerance Test

The OGTT is performed after the patient has been on a normal diet for at least 3 days and then has has fasted overnight for at least 10 hours on the evening before the test..

A baseline blood sample (the fasting blood sugar, or FBS) is taken after the overnight fast. The patient then drinks about 300ml of water containing 75g of glucose within 5 minutes. Plasma glucose levels are then measured every 30 minutes for 2 hours.

Throughout the test, the patient should be sitting comfortably and should refrain from exercising or smoking.


Indications for the Oral Glucose Tolerance Test

Many OGTTs are performed unnecessarily. There are relatively few indications for the test.

These include:

• Borderline fasting or post-prandial blood glucose

• Persistent glycosuria

• Glycosuria in pregnant women

• Pregnant women with a family history of DM and those who previously had large babies or unexplained fetal loss.

It is important to note that the OGTT is of little value in hospitalized patients or in patients immediately after a severe illness.


What are the expected results in a normal individual?

Click for video


Can you identify the abnormalities in this series of abnormal tests in the video above?

Click to take the self-assessment quiz.




    References Concerning the Diagnosis of Diabetes and Pre-Diabetes

    You may review or copy the articles available from the links below or click to link to useful web sites.



    • WHO Consultation on the Diagnosis of Diabetes, 1999 (PDF)
    • Diagnosis of Diabetes, NIH Publication (USA) (PDF)

    Useful links




knust sealumich


Programme Developed by


Francis A. Yeboah,

Head, Department of Molecular Medicine,

School of Medical Sciences, KNUST,

Kumasi, Ghana


Cary Engleberg, M.D.,

Departments of Internal Medicine, and Microbiology & Immunology,

University of Michigan Medical School,

Ann Arbor, Michigan. (



This programme was produced with support from the following: