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 to 12 hours. It helps doctors check for diabetes, prediabetes, or other blood sugar issues.

Quick summary

["A fasting glucose test helps assess your risk for diabetes and monitor blood sugar control."]

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

Key facts at a glance

LOINC
30252-1
Short code
Glucose 3.3h p Glc SerPl-sCnc
Synonyms
Glucose 3.3h p Glc SerPl-sCnc
Category
glucose
Sample
serum
Container
Red-top tube (SST)
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
CPT
82947
SNOMED
260395008
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?

Doctors order fasting serum glucose tests to diagnose conditions like type 1 or type 2 diabetes, prediabetes, or hypoglycemia (low blood sugar). It may also be used to monitor blood sugar levels in people with known diabetes or other metabolic disorders.

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. Your doctor or lab staff will provide instructions on how long to fast and what to avoid. Bring any medications you’re currently taking.

How the Test Is Done

A healthcare provider will draw blood from a vein in your arm. You may feel a small pinch, but it usually doesn’t cause significant discomfort. The blood sample will be sent to a lab for testing.

What the Results Mean

Results are typically reported in milligrams per deciliter (mg/dL). A fasting glucose level below 100 mg/dL is generally considered normal, while levels above 126 mg/dL may indicate diabetes. Your doctor will interpret the results in the context of your overall health.

Reference range

Fasting: 70-100 mg/dLN/A

Specimen: serum

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.

◆Associated findings1

Short name

Fasting Serum Glucose

Frequently asked questions

What does a fasting glucose test measure?
This test measures the amount of glucose (sugar) in your blood after you’ve fasted. It helps doctors check if your blood sugar is within a healthy range or if you have diabetes or another condition affecting sugar metabolism.
How long should I fast before this test?
You should fast for 8 to 12 hours before the test. This means no food or liquids (except water) for that time. Your doctor or lab will give you specific instructions to follow.
Can I take my medications before the test?
Yes, but check with your doctor first. Some medications may need to be adjusted or taken differently before fasting. Always follow your healthcare provider’s instructions.
  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