Serum/plasma glucose concentration (fasting)
This test measures the amount of glucose (sugar) in your blood after you’ve fasted for 8–12 hours. It helps doctors assess how well your body uses sugar for energy and check for conditions like diabetes.
["A fasting blood sugar test helps diagnose diabetes or prediabetes and monitor blood sugar control."]
Key facts at a glance
- LOINC
- 14752-0
- Short code
- Glucose 1.5h p Glc SerPl-sCnc
- Synonyms
- Glucose 1.5h p Glc 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 if you have symptoms like excessive thirst, frequent urination, unexplained weight changes, fatigue, or recurring infections. It’s also used to screen for diabetes, especially if you have risk factors like obesity, a family history of diabetes, or high blood pressure.
When Should You Fast?
You must fast (not eat or drink anything except water) for 8–12 hours before the test. Avoid caffeine, nicotine, or chewing gum during this time. Your doctor will provide specific instructions if you’re unsure.
What to Expect During the Test
A healthcare provider will draw blood from a vein in your arm. You may feel a small pinch, but it usually doesn’t cause discomfort. The blood sample is sent to a lab for analysis.
What Do Results Mean?
Results help determine if your blood sugar is too high or too low. High levels may indicate diabetes or insulin resistance, while very low levels could signal hypoglycemia (low blood sugar). Your doctor will discuss results with you in detail.
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.
This test plays a critical role in diagnosing diabetes and managing blood sugar levels. Abnormally high or low results may prompt further testing, such as an oral glucose tolerance test or hemoglobin A1c, to get a full picture of your metabolic health.
Short name
Fasting Blood Sugar
Frequently asked questions
What if I’m Pregnant or Have Diabetes?
Do I Need to Take Any Special Steps Before the Test?
Can I Drink Water 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