Glucose, 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 check how well your body uses sugar for energy.
["A fasting blood sugar test helps diagnose diabetes, prediabetes, or other blood sugar-related conditions."]
Key facts at a glance
- LOINC
- 1558-6
- Short code
- Glucose p fast SerPl-mCnc
- Synonyms
- Glucose p fast SerPl-mCnc
- Category
- glucose
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Ref low
- 10
- Ref high
- 40
- Critical range
- 50 N/A – 400 N/A
- Fasting
- true
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- CPT
- 84484
- SNOMED
- 302774002
- 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 evaluate your blood sugar levels, especially if you have symptoms like excessive thirst, frequent urination, unexplained weight loss, or fatigue. It can also be used during pregnancy (gestational diabetes screening) or to monitor chronic conditions like diabetes.
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 alcohol for at least 24 hours beforehand. Your blood will be drawn from a vein, usually in your arm, and you may feel a slight pinch or sting.
What Happens During the Test?
A healthcare provider will insert a small needle into your arm to collect a blood sample. The process takes only a few minutes, and you can resume normal activities afterward. The blood sample is sent to a lab for analysis.
What Does the Test Result Mean?
Results are typically reported in milligrams per deciliter (mg/dL). High or low results may indicate conditions like diabetes, hypoglycemia, or other metabolic issues. Your doctor will interpret the results in the context of your overall health.
Reference range
Adult: 10-40 U/LN/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.
Chronically high blood sugar (hyperglycemia) can damage blood vessels, nerves, and organs over time, increasing risks for heart disease, kidney problems, and nerve damage. Chronically low blood sugar (hypoglycemia) can cause dizziness, shakiness, or confusion. Fasting glucose tests are a key tool for early detection of blood sugar disorders.
Short name
Fasting Blood Sugar
Frequently asked questions
How long does it take to get my results?
What should I do if I have questions about my results?
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