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Glucose, Fasting Blood Draw (Serum or Plasma)

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 or other blood sugar issues.

Quick summary

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

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

Key facts at a glance

LOINC
76629-5
Short code
Glucose p fast Bld-sCnc
Synonyms
Glucose p fast Bld-sCnc
Category
glucose
Sample
whole-blood
Container
Lavender-top (EDTA)
Units
N/A
Ref low
10
Ref high
40
Critical range
50 N/A – 400 N/A
Fasting
true
Population
adult
Sex
all
Age range
18–65 years
CPT
84484
SNOMED
302774002
Specimen volume
3 mL
Stability
Room temperature: 4h, Refrigerated: 24h
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
4–24 hours
Order
routine

Why Is This Test Done?

Doctors order this test to diagnose diabetes, prediabetes, or other conditions affecting blood sugar. It may also be used during pregnancy, before surgery, or if you have symptoms like extreme thirst, fatigue, or unexplained weight changes.

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 blood will be drawn from a vein, usually in your arm, by a healthcare professional.

What Happens During the Test?

A small needle is inserted into your arm to draw a blood sample. The process takes a few minutes, and you may feel a brief pinch. The blood is then sent to a lab for testing.

What Are the Results Meaning?

Results are typically reported as a single number representing your blood sugar concentration. High or low levels may signal diabetes, insulin resistance, or other health concerns that need further evaluation.

Reference range

Adult: 10-40 U/LN/A

Specimen: whole-blood

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.

This test plays a critical role in diagnosing diabetes and managing blood sugar levels. Abnormally high or low results may prompt additional testing, such as an oral glucose tolerance test or hemoglobin A1c, to better understand your condition.

Short name

Fasting Blood Glucose

Frequently asked questions

How long does fasting last before this test?
You should fast for 8 to 12 hours before your test, meaning no food or liquids (except water) for that time.
Will I feel any pain during the blood draw?
You may feel a slight pinch or discomfort for a few seconds, but most people describe it as mild. The area may also feel tender afterward.
What if I miss my fasting window?
If you don’t fast properly, your results may not be accurate. Let your healthcare provider know if you accidentally eat or drink anything before your test.
  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