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 8–12 hours. It helps assess how well your body uses glucose for energy.

Quick summary

["Fasting glucose checks your blood sugar when you’re not eating, helping spot diabetes or metabolic issues early."]

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

Key facts at a glance

LOINC
33115-7
Short code
GA from HC.Merz88
Synonyms
GA from HC.Merz88
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
us-estimated-from-hc-merz
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 It Matters for Your Health

Your doctor may order this test to check for diabetes, prediabetes, or other conditions affecting blood sugar control. High or low levels can signal problems like insulin resistance or hormonal imbalances.

How the Test Works

A small blood sample is taken from your arm. The lab uses an automated method to measure glucose levels in your serum (liquid part of blood after clotting).

What to Expect Before the Test

You’ll need to fast (no food or drink except water) for 8–12 hours before the test. Avoid sugary drinks or snacks to get an accurate reading.

What the Results Mean

Results help determine if your blood sugar is within normal ranges or if further testing (like HbA1c) is needed. Your doctor will interpret the results based on your health history.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Fasting Serum Glucose

Frequently asked questions

Why did my doctor order this test?
Your doctor may recommend it if you have symptoms like frequent urination, excessive thirst, fatigue, or a family history of diabetes. It’s also part of routine check-ups for high-risk groups.
What if my fasting glucose is high?
If your results are above normal, your doctor might suggest lifestyle changes (like diet and exercise) or medications to manage blood sugar. Follow-up tests may be needed to monitor progress.
Can I eat or drink anything before the test?
No—fasting means no food or liquids (except water) for 8–12 hours before the test. Skipping this step could affect accuracy.
  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