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Glucose in Whole Blood (Fasting)

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

This test measures your blood sugar level after you’ve fasted for 8 to 12 hours. It helps check how well your body uses glucose, an important energy source.

Quick summary

["A fasting blood glucose test helps diagnose diabetes or prediabetes and monitor blood sugar control."]

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

Key facts at a glance

LOINC
49502-8
Short code
G6PD Bld Qn
Synonyms
G6PD Bld Qn
Category
glucose
Sample
whole-blood
Container
Lavender-top (EDTA)
Units
N/A
Fasting
true
Population
adult
Sex
all
Age range
18–65 years
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

Your doctor may order this test if you have symptoms like excessive thirst, frequent urination, unexplained weight changes, or fatigue. It’s also used during routine check-ups, especially for people at higher risk of diabetes.

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. Bring any medications you take daily with you, as some doctors may ask you to temporarily stop them.

How the Test Works

A healthcare provider will take a small blood sample from your arm using a needle. The sample is sent to a lab to measure glucose levels. The test is quick and usually done in a doctor’s office or lab.

What the Results Mean

Results are compared to a reference range, but exact values can vary by lab. High levels may indicate diabetes or insulin resistance, while low levels could signal hypoglycemia or other conditions.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Fasting Blood Glucose

Frequently asked questions

What causes high blood glucose?
High blood glucose can result from diabetes (either type 1 or type 2), poor diet, stress, illness, or certain medications. Regular monitoring helps manage the condition and prevent complications like nerve damage or heart disease.
How often should I get this test?
Frequency depends on your health status. People with diabetes may need tests every 3 to 6 months, while others with risk factors might get them annually. Follow your doctor’s recommendations.
Can I eat or drink anything before the test?
No, you must fast for 8 to 12 hours before the test. Only water is allowed. If you have questions about timing, ask your healthcare provider.
  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