Glucose, Serum (Fasting)
This test measures the amount of glucose (sugar) in your blood after you haven’t eaten for at least 8 hours. It helps check for conditions like diabetes or how well your body uses sugar for energy.
["A fasting glucose test helps assess blood sugar control and identify potential diabetes or metabolic issues."]
Key facts at a glance
- LOINC
- 55352-9
- Short code
- Glucose 45M p 75 g Glc PO SerPl-sCnc
- Synonyms
- Glucose 45M p 75 g Glc 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 Is This Test Done?
Your doctor may order this test to diagnose or monitor diabetes, prediabetes, or other blood sugar-related conditions. It’s also used to check for signs of high blood sugar, such as 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 smoking and excessive caffeine. Let your healthcare provider know about any medications you’re taking, as some may affect results.
How the Test Is Performed
A healthcare professional will draw blood from a vein in your arm using a small needle. You may feel a slight pinch, but it usually doesn’t cause discomfort. The blood sample is sent to a lab for analysis.
What the Results Mean
Results are compared to general reference ranges, but your specific values will depend on your health and medical history. High or low results may signal underlying issues that need further evaluation.
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 may indicate diabetes or insulin resistance, while persistently low levels could signal conditions like hypoglycemia or hormonal imbalances. Regular monitoring helps manage long-term health risks, such as heart disease or nerve damage.
Short name
Fasting Serum Glucose
Frequently asked questions
How long does fasting last before this test?
Can I take my usual medications before the test?
What happens if my fasting glucose is outside the normal range?
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