Glucose in Whole Blood (Fasting)
This test measures your blood sugar level after you’ve gone without food for 8 to 12 hours. It helps check how well your body uses glucose for energy.
["A fasting blood glucose test helps diagnose diabetes or other blood sugar issues."]
Key facts at a glance
- LOINC
- 2356-4
- Short code
- G6PD RBC Ql
- Synonyms
- G6PD RBC Ql
- Category
- glucose
- Sample
- whole-blood
- Container
- Lavender-top (EDTA)
- Units
- N/A
- Ref low
- 4.2
- Ref high
- 5.9
- Critical range
- 2 N/A – 7 N/A
- Fasting
- true
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- CPT
- 85041
- SNOMED
- 900000000000003001
- 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 Matters
Your doctor may order this test to check for diabetes, prediabetes, or other conditions that affect blood sugar. It’s also used to monitor blood sugar levels in people already diagnosed with diabetes.
When You Might Need It
You’ll typically need to fast (not eat or drink anything except water) for 8 to 12 hours before this test. Your doctor will schedule it during a routine blood draw, usually in the morning.
What to Expect During the Test
A healthcare professional will insert a small needle into your arm to draw a small amount of blood. You may feel a slight pinch, but it usually doesn’t cause pain. The blood is then sent to a lab for testing.
What the Results Mean
Results are usually reported in milligrams per deciliter (mg/dL). While exact ranges vary by lab, higher than normal levels may indicate diabetes or insulin resistance, while lower levels could suggest hypoglycemia (low blood sugar).
Reference range
Adult males: 4.2-5.9; Females: 3.8-5.1 x 10^12/LN/A
No special preparation required. Stay well hydrated.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Elevated fasting blood glucose levels are a key indicator of diabetes mellitus. It helps identify whether you have prediabetes (blood sugar levels higher than normal but not yet diabetic) or full-blown diabetes. Regular monitoring is important for managing blood sugar, especially if you have risk factors like obesity, a family history of diabetes, or high blood pressure.
Short name
Fasting Blood Glucose
Frequently asked questions
How long does it take to get my results?
What should I do if my fasting blood glucose is high?
Can I drink water before the test?
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 17, 2026. · Read our editorial policy