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Serum/plasma glucose concentration (fasting)

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

This test measures the amount of glucose (sugar) in your blood after you’ve fasted for 8 to 12 hours. It helps assess how well your body uses sugar for energy and can indicate diabetes or other metabolic conditions.

Quick summary

["A fasting blood sugar test checks your body’s ability to manage glucose levels."]

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

Key facts at a glance

LOINC
30253-9
Short code
Glucose 3.6h p Glc SerPl-sCnc
Synonyms
Glucose 3.6h 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?

Your healthcare provider may order this test to check for diabetes, prediabetes, or other blood sugar-related conditions. It’s also used to monitor treatment for existing 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 provider will give you specific instructions. Bring your appointment details and any medications you’re taking.

How the Test Is Performed

A healthcare professional will draw blood from a vein in your arm using a small needle. You may feel a slight pinch, but it usually doesn’t cause much discomfort. The blood sample is sent to a lab for analysis.

What the Results Mean

The results help determine if your blood sugar is too high or too low. While exact ranges depend on your health and medical history, abnormal results may trigger further testing or adjustments to your treatment plan.

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 Blood Sugar

Frequently asked questions

What does a normal fasting blood sugar level mean?
A normal fasting blood sugar level is typically within the range your healthcare provider specifies. If your results fall outside this range, you may need additional testing or follow-up to understand why.
How long does it take to get my results?
Results are usually available within 1 to 3 business days, depending on your lab and healthcare provider. Follow-up instructions will be provided once you receive your results.
Can I eat or drink anything before this test?
No, you must fast for 8 to 12 hours before the test, excluding water. Avoid caffeine, alcohol, or sugary drinks during this time to ensure accurate results.
  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