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Glucose in Serum (Fasting, 8-Hour)

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

This test measures your blood sugar level after fasting for at least 8 hours. It helps assess how well your body uses glucose for energy.

Quick summary

["A fasting glucose test is crucial for diagnosing diabetes or other metabolic conditions."]

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

Key facts at a glance

LOINC
14751-2
Short code
Glucose 1.5h p 50 g Lac PO SerPl-sCnc
Synonyms
Glucose 1.5h p 50 g Lac PO 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?

Your healthcare provider may order this test to check for diabetes, prediabetes, or other blood sugar-related issues. It’s also used to monitor existing conditions like diabetes or to evaluate symptoms such as excessive thirst, frequent urination, or unexplained weight changes.

What to Expect Before the Test

You’ll need to fast for 8 hours before the test, meaning no food or drink (except water) for that time. Avoid smoking and excessive caffeine. Bring any medications you’re currently taking, as some may affect results.

During the Test

A healthcare professional will draw blood from a vein, usually in your arm. You may feel a slight pinch, but the process is quick. The blood sample will be sent to a lab for analysis.

What the Results Mean

The results help determine if your blood sugar is within a healthy range or if further testing or treatment is needed. High or low levels can indicate health risks that require medical attention.

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.

Elevated fasting glucose levels may signal diabetes or insulin resistance, while persistently low levels could indicate conditions like hypoglycemia or certain hormonal disorders. Regular monitoring is essential for managing metabolic health.

Short name

Fasting Serum 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) during that time. Your provider may specify a longer fast if needed.
Can I take my usual medications before the test?
Yes, but always check with your healthcare provider first. Some medications may affect your blood sugar, so they may advise adjusting timing or dosage.
What if I forget to fast?
If you don’t fast as directed, your results may not be accurate. Re-schedule the test and follow your provider’s instructions for proper fasting.
  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