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Glucose in Serum (Fasting)

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

This test measures your blood sugar level after you haven’t eaten for at least 8 hours. It helps check for diabetes or other blood sugar issues.

Quick summary

["A fasting blood glucose test helps diagnose diabetes or monitor blood sugar levels over time."]

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

Key facts at a glance

LOINC
56982-2
Short code
GH 90M p resting SerPl-mCnc
Synonyms
GH 90M p resting SerPl-mCnc
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
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 check for diabetes, prediabetes, or high blood sugar. It’s also used to monitor existing diabetes treatment effectiveness or screen for conditions like hypoglycemia (low blood sugar).

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. Bring any medications you’re currently taking, as some may affect results. Wear comfortable clothing and plan to stay near the testing site for a short time.

How the Test Works

A healthcare professional will draw blood from a vein in your arm. The blood sample is sent to a lab to measure glucose levels using an automated analyzer. The test is quick and typically painless, though you may feel a slight pinch.

What the Results Mean

Results are compared to standard reference ranges, but your doctor will interpret them in the context of your health history. Abnormally high or low levels may trigger further testing or adjustments to treatment.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Fasting Blood Glucose

Frequently asked questions

How long does fasting last for this test?
You must fast for at least 8 hours before the test, meaning no food or drink (except water) for that period. Your doctor may specify a longer fast if needed for accuracy.
Can I take my medications before the test?
Yes, but check with your doctor first. Some medications (like insulin or certain diabetes drugs) may affect results, so they may advise adjusting timing or dosage.
What if I feel dizzy or weak before the test?
This could signal low blood sugar. If you experience symptoms, eat a small snack (like a glucose tablet or hard candy) and inform the phlebotomist immediately. They may pause the test or adjust the procedure.
  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