Fasting Blood Glucose (Serum) with Glucose Tolerance Test (Oral)
This test measures your blood sugar levels before and after drinking a sugary liquid to check how your body processes glucose. It helps diagnose conditions like diabetes or identify how your body responds to glucose.
["This test helps assess your blood sugar control and potential diabetes risk."]
Key facts at a glance
- LOINC
- 41604-0
- Short code
- Glucose p fast BldC Glucomtr-mCnc
- Synonyms
- Glucose p fast BldC Glucomtr-mCnc
- Category
- glucose
- Sample
- whole-blood
- Container
- Lavender-top (EDTA)
- Units
- N/A
- Ref low
- 10
- Ref high
- 40
- Critical range
- 50 N/A – 400 N/A
- Fasting
- true
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- glucometer
- CPT
- 84484
- SNOMED
- 302774002
- Specimen volume
- 3 mL
- Stability
- Room temperature: 4h, Refrigerated: 24h
- Hemolysis max
- 0
- Lipemia max
- 0
- Icterus max
- 0
- TAT
- 4–24 hours
- Order
- routine
Why This Test Is Done
Your doctor may order this test if you have symptoms of high or low blood sugar, a family history of diabetes, or if you’re at risk for metabolic issues. It’s also used to monitor existing diabetes or prediabetes.
How the Test Works
You’ll first fast for 8–12 hours. After fasting, a blood sample is drawn to measure your baseline glucose level. Then, you’ll drink a sugary solution, and blood samples will be taken at set intervals (e.g., 30 minutes, 1 hour, 2 hours) to track how your blood sugar rises and falls.
What to Expect Before the Test
Avoid eating or drinking anything except water for 8–12 hours before the fasting blood draw. If you’re pregnant, have kidney disease, or take certain medications, let your doctor know—these may affect results.
What to Expect During the Test
You’ll sit quietly while a healthcare provider takes blood samples from your arm. The process is quick and usually painless, though you may feel a slight pinch. The oral glucose challenge involves drinking a sweet liquid and additional blood draws afterward.
Reference range
Adult: 10-40 U/LN/A
Fasting for 8-12 hours required. Water is permitted. Avoid chewing gum and smoking before the test.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Abnormal results may indicate diabetes (high blood sugar) or impaired glucose tolerance. Low fasting glucose could signal hypoglycemia or other metabolic disorders. This test helps guide treatment plans, such as medication adjustments or lifestyle changes.
Short name
Fasting Blood Glucose + Glucose Tolerance Test
Frequently asked questions
How long does the fasting period last?
What should I eat or drink during the fasting period?
Will the oral glucose drink taste bad?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy