Glucose in Serum (Fasting)
This test measures the amount of glucose (sugar) in your blood after you’ve gone without food for at least 8 hours. It helps doctors check how well your body is using sugar for energy and can help detect diabetes or other metabolic conditions.
["A fasting glucose test helps assess blood sugar control and identify potential diabetes or other health risks."]
Key facts at a glance
- LOINC
- 39478-3
- Short code
- Glucose Vitf-sCnc
- Synonyms
- Glucose Vitf-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 Is This Test Done?
Doctors order fasting serum glucose tests to diagnose diabetes, monitor blood sugar levels in people with diabetes, or check for conditions like hypoglycemia (low blood sugar). It may also be used during pregnancy (gestational diabetes) or before certain treatments.
What to Expect Before the Test
You’ll need to fast (not eat or drink anything except water) for 8–12 hours before the test. Avoid alcohol and strenuous activity. Bring any medications you’re taking to discuss with your provider.
How the Test Is Done
A healthcare professional will draw blood from a vein in your arm. You may feel a slight pinch, but it’s usually over quickly. The blood sample is sent to a lab for analysis.
What the Results Mean
Results are reported in milligrams per deciliter (mg/dL) or millimoles per liter (mmol/L). High results may indicate diabetes or insulin resistance, while very low results could signal hypoglycemia. Your doctor will interpret results in the context of your overall health.
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.
High fasting glucose levels (above normal ranges) are a key diagnostic marker for type 2 diabetes. Repeatedly elevated results may prompt further testing, like an A1C or oral glucose tolerance test. Low levels can cause fatigue, dizziness, or confusion, requiring medical attention.
Short name
Fasting Serum Glucose
Frequently asked questions
What causes fasting serum glucose to be high?
What should I do if my fasting glucose is high?
Can I eat or drink anything before my fasting 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 16, 2026. · Read our editorial policy