Glucose in Serum (Fasting)
This test measures the amount of glucose (sugar) in your blood after you’ve fasted for at least 8 hours. It helps check how well your body uses sugar for energy.
["A fasting blood glucose test helps assess your blood sugar levels and identify potential diabetes or insulin resistance."]
Key facts at a glance
- LOINC
- 45298-7
- Short code
- Glucose 2.5h p 50 g Lac PO SerPl-sCnc
- Synonyms
- Glucose 2.5h p 50 g Lac PO SerPl-sCnc
- Category
- glucose
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Ref low
- 70
- Ref high
- 100
- Critical range
- 50 N/A – 400 N/A
- Fasting
- true
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- CPT
- 82947
- SNOMED
- 260395008
- Specimen volume
- 5 mL
- Stability
- Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 4–24 hours
- Order
- routine
Why This Test Is Done
Your healthcare provider may order this test to diagnose or monitor conditions like diabetes, prediabetes, or to check for high blood sugar levels. It’s also used before certain treatments or surgeries to ensure stable blood sugar.
What to Expect Before the Test
You’ll need to fast (not eat or drink anything except water) for 8 to 12 hours before the test. Avoid smoking and excessive alcohol. Bring any medications you’re taking to your appointment.
How the Test Is Done
A healthcare professional will draw blood from a vein in your arm using a small needle. You may feel a brief pinch, but it usually doesn’t cause pain. The blood sample is sent to a lab for analysis.
What the Results Mean
The results provide a snapshot of your blood sugar level at the time of testing. While specific ranges vary by lab, higher or lower levels may signal concerns that need further evaluation by your doctor.
Reference range
Fasting: 70-100 mg/dLN/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.
Elevated fasting glucose levels may indicate diabetes or insulin resistance, while persistently low levels could suggest conditions like hypoglycemia or hormonal imbalances. Regular monitoring helps manage blood sugar and prevent long-term complications.
Short name
Fasting Blood Glucose
Frequently asked questions
How long does fasting last before this test?
Can I take my usual medications before the test?
What if I’m not sure if I’ve fasted long enough?
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