Quick Facts
- Sample: Blood
- Fasting: Fast for at least 8 hours before testing; only water is permitted. A fasting blood specimen is collected before drinking a 75 g glucose solution, followed by two additional blood draws at 1 and 2 hours.
- Turnaround: 1-2 business days. May take longer based on weather, holiday, or lab delays.
What This Test Measures
This test measures your glucose (blood sugar) levels at three separate points to assess how your body processes glucose over a 2-hour period. The first specimen is drawn while you are fasting, then you drink a 75g glucose solution at the lab, and two additional specimens are collected at 1 hour and 2 hours afterward.
By comparing these three timed glucose readings, this test shows how your glucose levels rise and then return toward baseline after a glucose challenge. It reflects your current glucose response at each specific time point rather than your average glucose levels over weeks or months.
Benefits
- Tracks how your body processes glucose over a 2-hour window.
- Captures fasting, 1-hour, and 2-hour glucose values in one visit.
- Provides timed data often used to help evaluate Type 2 Diabetes.
- Shows how glucose levels change after a standardized glucose challenge.
- Offers three data points instead of a single glucose reading.
Who Is This Test For?
- Individuals whose healthcare provider has recommended assessing glucose tolerance.
- People being evaluated for Type 2 Diabetes as part of a broader workup.
- Individuals who want timed glucose data beyond a single fasting result.
- Those following up on prior glucose test results with their provider.
- People who can commit to at least 2 hours for the full collection process.
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 10-12 hours is required before your appointment. Three days prior to testing, you should discontinue all nonessential medication that can affect glucose metabolism, and check with your physician before stopping any medications. Plan to spend at least 2 hours at the lab, since specimens are collected fasting, then 1 hour and 2 hours after drinking a glucose solution provided on site.
2. How quickly will I get results?
Results are generally available in 1-2 days. Turnaround may take longer based on weather, holidays, or lab delays.
3. What can my results tell me?
Comparing your three glucose readings can show how your body handles a glucose load over time, including whether your levels rise and return toward baseline as expected within the 2-hour window. This timed pattern is one piece of information a healthcare provider may use when evaluating glucose metabolism.
4. What factors can affect my results?
Not completing the required 10-12 hour fast can alter your fasting result and affect the accuracy of the entire test. Medications that influence glucose metabolism can also affect your readings if they are not discontinued as instructed beforehand. Timing matters as well, since the 1-hour and 2-hour specimens must be collected at the correct intervals after the glucose solution to reflect an accurate response.
5. How do I interpret the results?
Interpreting a 3-specimen, 2-hour glucose tolerance test depends on how your fasting, 1-hour, and 2-hour values compare to one another, along with your symptoms, medical history, and any other relevant laboratory findings. A single abnormal timed value does not by itself confirm diabetes, and a normal pattern does not by itself rule it out. Your healthcare provider is best positioned to place these results in context.
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?
Share your results with a qualified healthcare provider for review. An abnormal timed glucose value does not automatically mean a diagnosis or require treatment, and your provider can determine whether additional evaluation or testing is appropriate based on your full clinical picture.
Pre-test preparation
Fast for at least 8 hours before testing. During the fasting period, only water is permitted. This test requires three blood specimens. The first specimen will be collected while fasting, before you are given a 75 g glucose solution to drink. Two additional specimens will be collected at 1 and 2 hours after drinking the glucose solution. Please allow at least 2 hours for the collection process.
