Fasting Blood Glucose Test
A fasting blood glucose test measures the amount of sugar (glucose) in your blood after you have not eaten or drunk anything except water for 8-12 hours. This simple blood test helps your doctor see how well your body manages blood sugar and is commonly used to screen for diabetes and prediabetes.
{"Measures blood sugar level after fasting","Used to diagnose diabetes and prediabetes","Normal range is typically 70-100 mg/dL","Requires 8-12 hours of fasting before the test","Higher levels may indicate diabetes or prediabetes"}
Key facts at a glance
- LOINC
- 1554-5
- Short code
- Fasting Glucose
- Synonyms
- —
- Category
- glucose
- Sample
- plasma
- Container
- Gray Top Tube (sodium fluoride/potassium oxalate) or Green Top Tube (sodium heparin)
- Units
- mg/dL
- Ref low
- 70
- Ref high
- 99
- Critical range
- 40 mg/dL – 250 mg/dL
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- ≥ 18 years
- Method
- hexokinase
- CPT
- 82947
- SNOMED
- 271252004
- Specimen volume
- 2-3 mL
- Stability
- Room temperature: 24-72 hours, Refrigerated (2-8°C): 7 days, Frozen (-20°C or below): several months. Protect from light.
- Hemolysis max
- 50
- Lipemia max
- 300
- Icterus max
- 20
- TAT
- 1–2 hours
What is this test?
The fasting blood glucose test, also known as fasting plasma glucose (FPG), is a simple blood test that measures the amount of glucose (sugar) in your blood after you have fasted for 8 to 12 hours. This test is one of the most common ways to check how your body manages blood sugar and is primarily used to screen for and diagnose diabetes and prediabetes.
Why is this test important?
This test is crucial because it helps healthcare providers detect diabetes early, before complications develop. It is also used to monitor blood sugar levels in people who have already been diagnosed with diabetes. Regular monitoring can help prevent serious health problems related to diabetes, such as heart disease, kidney damage, and vision problems.
How is the test performed?
A healthcare professional will draw a blood sample from a vein in your arm using a small needle. The blood is collected into a test tube or vial. You may feel a slight sting or pinch when the needle is inserted. The procedure typically takes only a few minutes, and the sample is sent to a laboratory for analysis.
How to prepare for the test?
To ensure accurate results, you should fast (not eat or drink anything except water) for 8 to 12 hours before the test. It is important to inform your healthcare provider about any medications you are taking, as certain drugs can affect blood glucose levels. Avoid smoking, drinking coffee, or chewing gum before the test, as these can also impact results.
Reference range
Normal fasting glucose: 70-100 mg/dL (3.9-5.6 mmol/L). Prediabetes (Impaired Fasting Glucose): 100-125 mg/dL (5.6-6.9 mmol/L). Diabetes: ≥126 mg/dL (≥7.0 mmol/L) on two separate occasions. Results should be interpreted in clinical context.mg/dL
Although fasting is not strictly required for this test, an 8-12 hour fast is recommended for most accurate interpretation. Patient should avoid smoking, caffeine, and vigorous exercise before specimen collection. Inform physician of current medications as certain drugs (corticosteroids, beta-blockers, diuretics) may affect glucose levels.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
The fasting blood glucose test results are interpreted as follows: Normal fasting glucose is less than 100 mg/dL (5.6 mmol/L). Prediabetes (impaired fasting glucose) is indicated by levels between 100-125 mg/dL (5.6-6.9 mmol/L). Diabetes is diagnosed when fasting glucose is 126 mg/dL (7.0 mmol/L) or higher on two separate occasions. These results help healthcare providers determine appropriate treatment plans and lifestyle modifications.
Short name
FBS
Part of panels
Frequently asked questions
Can I drink water before the test?
What if my results show prediabetes?
How often should I have this test?
Does stress affect fasting blood glucose?
Sources
- 1
- 2
- 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 10, 2026. · Read our editorial policy