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Glucose in Blood (Fasting)

Published: August 9, 2026Updated: August 16, 2026

This test measures the amount of glucose (sugar) in your blood after you’ve fasted for a set period. It helps doctors check how well your body uses sugar for energy.

Quick summary

["A fasting blood glucose test helps diagnose diabetes or other blood sugar issues."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
41653-7
Short code
Glucose BldC Glucomtr-mCnc
Synonyms
Glucose BldC Glucomtr-mCnc
Category
glucose
Sample
whole-blood
Container
Lavender-top (EDTA)
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
Method
glucometer
CPT
82947
SNOMED
260395008
Specimen volume
3 mL
Stability
Room temperature: 4h, Refrigerated: 24h
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
4–24 hours
Order
routine

Why This Test Matters

Fasting means you shouldn’t eat or drink anything—except water—8 to 12 hours before your blood draw. This helps give the most accurate reading of your blood sugar levels when your body is resting.

How the Test Works

A small sample of your blood is taken from a vein, usually in your arm. The lab then measures the glucose concentration using an enzymatic method, which detects sugar levels precisely.

What to Expect Before the Test

You’ll likely be asked to arrive early to fast. Wear comfortable clothing and bring any medications you take daily. If you have a medical condition or concerns, let your provider know.

Possible Results & Next Steps

Results may be used to diagnose conditions like diabetes, prediabetes, or hypoglycemia. Your doctor will discuss findings with you and may recommend follow-up tests or lifestyle changes.

Reference range

Fasting: 70-100 mg/dLN/A

Specimen: whole-blood

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 is critical for diagnosing diabetes, monitoring blood sugar control in people with diabetes, or identifying prediabetes. Abnormally high or low levels can indicate metabolic disorders or other health risks.

Short name

Fasting Blood Glucose

Frequently asked questions

What does a normal fasting blood glucose level mean for me?
A normal fasting blood glucose level is typically below a certain threshold (varies by lab and clinical context). Your doctor will interpret results based on your overall health and medical history.
How long does it take to get my results?
Results are usually available within 1 to 3 business days, depending on your lab. Your doctor will contact you once they’re ready for discussion.
Can I eat or drink anything before this test?
No, you must fast for 8 to 12 hours before the test, excluding water. Avoid caffeine, sugary drinks, or snacks to ensure accurate results.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

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.

Medical Disclaimer

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