Quick Facts
- Sample: Venous blood (3 draws)
- Fasting: 10–12 hours required
- Turn-around: 1-2 business days. May take longer based on weather, holiday or lab delays.
Benefits
- Comprehensive glucose assessment - Three timepoints reveal how your body processes sugar over time
- Early detection advantage - Identifies prediabetes and diabetes before symptoms develop
- Gold standard accuracy - More sensitive than single glucose tests or A1C alone
- Convenient direct access - Order online without doctor's prescription at 3,000+ locations
- Cost-effective screening - Avoid multiple provider visits while getting clinical-grade results
- Proactive health monitoring - Take control of your metabolic health with WHO-standardized testing
Who Is This Test For?
- Adults 35+ following updated CDC screening guidelines
- Individuals with diabetes risk factors (family history, overweight, high blood pressure)
- People from high-risk ethnicities (African American, Latino, Native American, Asian American, Pacific Islander)
- Those with borderline results on previous glucose tests
- Anyone experiencing diabetes symptoms (increased thirst, frequent urination, fatigue)
- Health-conscious individuals wanting comprehensive metabolic baseline data
How It Works – Just 3 Steps
- Fast & arrive - Fast 10-12 hours, then visit your chosen lab location
- Drink & wait - Give fasting blood sample, drink glucose solution, remain at lab
- Complete testing - Provide blood samples at 1-hour and 2-hour intervals
FAQ
What makes this test different from a regular blood glucose test? The 3-specimen GTT tracks how your body processes glucose over time, providing comprehensive insights that single-point tests miss.
How long does the entire test take? Plan for 2-3 hours at the lab — you'll need to remain there for all three blood draws.
Can I take medications before the test? Discontinue non-essential medications affecting glucose for three days prior, but consult your physician first.
What should I eat before fasting? Consume a mixed diet with at least 150g carbohydrates daily for three days before your test.
When will I get my results? Results are typically available in 1-2 business days and delivered securely to your online account.
More Details
What is the purpose of this test?
The 2-hour Glucose Tolerance Test measures how efficiently your body processes glucose over time, providing a comprehensive assessment of your metabolic health. Unlike single-point glucose tests, this three-specimen approach tracks your body's glucose response at fasting, 1-hour, and 2-hour intervals after consuming a standardized 75g glucose solution. This method is considered the gold standard for diagnosing diabetes and prediabetes (Mayo Clinic 2024).
The test reveals crucial information about insulin function and glucose metabolism that other tests might miss. Research shows that fasting plasma glucose alone has only 58.14% sensitivity compared to the complete GTT (PubMed 2023).
Who would benefit from this test?
This test is particularly valuable for adults with diabetes risk factors, including family history, overweight/obesity, high blood pressure, or certain ethnicities (African American, Latino, Native American, Asian American, Pacific Islander). Current guidelines recommend screening for all adults starting at age 35 (ADA 2024).
Individuals who have had borderline results on other glucose tests, those experiencing symptoms like increased thirst or frequent urination, and anyone planning significant lifestyle changes who wants baseline metabolic data will find this test especially informative.
When should I order this test?
Consider ordering when you have risk factors for diabetes but no symptoms yet, you've received borderline results on other glucose tests, you're planning significant lifestyle changes and want baseline data, or it's been 3+ years since your last screening and you're over 35. Updated screening guidelines have made an additional 12-14 million US adults eligible for glucose testing (CDC 2024).
The test is also recommended if you're experiencing unexplained fatigue, increased thirst, frequent urination, or other symptoms that might suggest glucose metabolism issues.
How do I interpret the results?
Your results will show glucose levels at three timepoints. Here's how to interpret them:
Fasting
- Normal: <100 mg/dL
- Prediabetes: 100–125 mg/dL
- Diabetes: ≥126 mg/dL
1-hour
- Normal: <180 mg/dL
- Prediabetes: N/A
- Diabetes: N/A
2-hour
- Normal: <140 mg/dL
- Prediabetes: 140–199 mg/dL
- Diabetes: ≥200 mg/dL
The 1-hour value of ≥155 mg/dL may indicate increased future diabetes risk even if other values are normal.
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.
Pre-test preparation
Fast for 10-12 hours before your appointment (water is permitted). Consume a mixed diet with at least 150g of carbohydrates daily for three days before the test. Discontinue non-essential medications that affect glucose metabolism for three days prior, but consult your physician first.
Schedule a morning appointment when possible and bring entertainment for waiting periods. Plan to remain at the lab for the entire 2-3 hour duration.
How often should I get tested?
- Normal results: Every 3 years
- Risk factors present: Every 1–2 years
- Prediabetes diagnosis: Annually
- Diabetes indications: Immediate follow-up with healthcare provider
Why early detection matters
More than 98 million Americans have prediabetes, and 81% don't know they have it (CDC 2023). The economic burden of prediabetes reached $43.4 billion in 2017, costing $500 annually per person (AMA 2024).
Early detection through comprehensive testing like the GTT enables lifestyle interventions that can prevent or delay diabetes development. Even 5-7% weight loss in prediabetic individuals can significantly reduce progression to diabetes.
Related tests you may consider
Hemoglobin (Hb) A1c Blood Test - Calculates the average blood glucose levels over 2-3 months, making it an ideal diagnostic tool for diabetes management.
Comprehensive Metabolic Panel (CMP-14) with eGFR Blood Test - Evaluates nutrient levels, liver, and kidney function.
Insulin Response Blood Test, 3 Specimens - Measures insulin levels in response to glucose to help screen for hypoglycemia and suspected insulin resistance.
