Glucose in Serum (Fasting)
This test measures the amount of glucose (sugar) in your blood after you’ve fasted for 8 to 12 hours. It helps doctors assess your blood sugar levels and check for conditions like diabetes.
["A fasting glucose test helps diagnose or monitor blood sugar control."]
Key facts at a glance
- LOINC
- 1518-0
- Short code
- Glucose 2h p 75 g Glc PO SerPl-mCnc
- Synonyms
- Glucose 2h p 75 g Glc PO SerPl-mCnc
- 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 check for diabetes or prediabetes, evaluate blood sugar levels before treatments, or monitor existing diabetes management. It’s also used in some screening programs for heart disease or kidney problems.
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. Your blood will be drawn from a vein, usually in your arm. The process takes a few minutes, and you may feel a slight pinch.
What Happens During the Test?
A healthcare provider will clean the area with an antiseptic, insert a small needle into your vein, and collect a blood sample into a tube. The needle will be removed once the sample is taken, and you’ll be given pressure to stop any bleeding.
How the Results Are Used
Results are compared to standard reference ranges to determine if your blood sugar is within normal limits, low, or high. High levels may indicate diabetes or insulin resistance, while low levels could signal hypoglycemia or other health issues.
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.
Abnormally high fasting glucose levels often signal diabetes or prediabetes, which can increase risks for heart disease, nerve damage, kidney problems, and vision issues. Consistently low levels may require medical attention to prevent dangerous drops in blood sugar, especially if you’re diabetic or taking medications that affect glucose.
Short name
Fasting Serum Glucose
Frequently asked questions
How long does it take to get my results?
What if my fasting glucose is higher than normal?
Can I eat or drink anything 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 16, 2026. · Read our editorial policy