Skip to content

Glucose in Serum (Fasting)

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

This test measures your blood sugar level after you’ve fasted for a set period, often used to assess how your body processes glucose.

Quick summary

["Fasting blood sugar helps diagnose diabetes or other metabolic conditions."]

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

Key facts at a glance

LOINC
15347-8
Short code
GH 30M p chal SerPl-mCnc
Synonyms
GH 30M p chal 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 other blood sugar-related disorders. It’s also used to monitor existing conditions like high blood sugar or to evaluate how your body responds to treatments.

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. Avoid sugary foods, drinks, or smoking. Bring any medications you’re taking to discuss with your healthcare provider.

During the Test

A healthcare professional will draw blood from a vein in your arm. You may feel a slight pinch, but it’s quick and usually not painful. The test itself takes only a few minutes.

What the Results Mean

Results are compared to standard reference ranges, but your doctor will interpret them in the context of your health history and symptoms. High or low readings may trigger further testing or lifestyle adjustments.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance: Glucose levels outside normal ranges can signal diabetes, insulin resistance, or other metabolic disorders. Persistently high or low levels may require medical management, including diet, exercise, or medication.

Short name

Fasting Serum Glucose

Frequently asked questions

How long does fasting last for this test?
Typically, you must fast for 8 to 12 hours before the test, including no food or liquids (except water) except during that period.
Can I take my usual medications before the test?
Some medications may need adjustment. Always inform your doctor or lab technician about all medications, including over-the-counter drugs or supplements, before the test.
What if I have diabetes and my blood sugar is already checked at home?
A fasting serum glucose test provides a more standardized measurement compared to home monitoring, especially useful for diagnosing diabetes or assessing treatment effectiveness. Follow your doctor’s guidance for the best approach.
  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