Quick Facts
- Sample: Blood
- Fasting: Fasting for 10–12 hours is required; check with your physician before stopping medications. Two blood draws are taken: fasting and 2 hours after drinking a glucose solution. Allow at least 2 hours for testing.
- Turnaround: 1-2 business days. May take longer based on weather, holiday, or lab delays.
What This Test Measures
This test measures your blood glucose level at two separate points using the oral WHO protocol. The first sample is drawn after a 10- to 12-hour fast, and the second is drawn two hours after you drink a solution containing 75 grams of glucose. Together, these two specimens show how your blood sugar responds to a glucose challenge over a defined two-hour period.
Because the test relies on two timed specimens rather than a single reading, it captures how your body processes glucose over time, not just your glucose level at one moment. This distinguishes it from a single fasting or random glucose measurement, since it tracks the rise and fall of blood sugar across the full two-hour window.
Benefits
- Measures blood glucose response over a defined two-hour window
- Captures both fasting and post-glucose blood sugar levels
- Uses a standardized 75-gram oral glucose challenge
- Supports tracking of glucose-related treatment progression
- Provides two timed specimens for a fuller glucose response picture
Who Is This Test For?
- Individuals whose healthcare provider wants to assess glucose response over time
- People being evaluated for how their body processes a glucose challenge
- Individuals being monitored for changes in glucose-related treatment
- People whose provider has recommended a two-specimen glucose tolerance test
How It Works
- Order Your Test Online
- Visit a Local Lab
- Get Results Online
FAQ
1. Do I need to fast or prepare for this test?
Fasting for 10 to 12 hours is required before your first blood draw. During the fast, you may drink water and take medications, but three days prior to testing you should discontinue any nonessential medication that can affect glucose metabolism, after checking with your physician. Plan to spend at least two hours at the lab, since the test requires a fasting sample followed by a second sample two hours after drinking a glucose solution.
2. How quickly will I get results?
Results are typically available in 1 to 2 days, though this timeframe may be extended due to weather, holidays, or other lab delays. Your specific turnaround may vary depending on the testing lab you visit.
3. What can my results tell me?
Comparing your fasting glucose level to your two-hour glucose level shows how your blood sugar rises and returns toward baseline after a glucose challenge. This pattern can help a healthcare provider track glucose-related treatment progression or evaluate how your body responds to glucose. A single set of results reflects that one testing session rather than a complete, ongoing picture of your glucose metabolism.
4. What factors can affect my results?
Not completing the full 10 to 12 hour fast can affect your fasting result, and inconsistent timing of the two-hour draw can affect how the response is measured. Medications that influence glucose metabolism may also alter your results if they are not discontinued beforehand as directed by your physician. Because the test depends on two precisely timed specimens, any deviation from the fasting window or the two-hour collection interval can change how the results are interpreted.
5. How do I interpret the results?
Interpreting glucose tolerance results depends on comparing your fasting value to your two-hour value and considering your overall clinical picture, including any medications or health conditions that may affect glucose metabolism. A result outside the expected range does not by itself confirm or rule out a specific diagnosis. Discuss your specific values and what they may mean with a qualified healthcare provider.
Disclaimer: Reference ranges may vary by laboratory. Listed ranges are general guidelines and may differ from those used by the performing lab. Always consult your healthcare provider for interpretation.
6. What should I do if my results are abnormal?
Bring your results to a qualified healthcare provider for review in the context of your overall health. Do not stop prescribed medication unless instructed by your healthcare provider. Your provider may consider additional evaluation or testing based on your results and individual circumstances.
Pre-test preparation
Fasting for 10-12 hours is required before this test. Three days prior to testing, discontinue all nonessential medication that can affect glucose metabolism, and check with your physician before stopping any medications. This test is collected as 2 specimens: a fasting sample, and a second sample taken 2 hours after drinking a glucose solution at the lab. Please schedule at least 2 hours of time for your collection.
