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Serum/plasma concentration of glucose (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 your doctor check how well your body uses glucose for energy.

Quick summary

["A fasting blood sugar test helps assess your blood glucose control, especially if you have diabetes or risk factors for it."]

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

Key facts at a glance

LOINC
73359-2
Short code
glyBURIDE ind plt IgG SerPl Ql FC
Synonyms
glyBURIDE ind plt IgG SerPl Ql FC
Category
hematology
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
flow-cytometry
CPT
82784
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’s Done

Your doctor may order this test to diagnose diabetes, monitor diabetes management, or check for conditions like hypoglycemia (low blood sugar). It’s also used to evaluate how your body processes glucose over time.

What to Expect

You’ll fast (no food or drink except water) for the specified period before the test. A healthcare provider will draw blood from a vein, usually in your arm. The process takes a few minutes.

How It Works

Blood is collected and sent to a lab, where it’s analyzed to measure the amount of glucose present. The test detects glucose levels in your serum or plasma, depending on the sample type used.

What the Results Mean

Results help determine if your blood sugar is within a healthy range or if adjustments to diet, medication, or lifestyle are needed. Your doctor will interpret the results in the context of your overall health.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Fasting Blood Sugar

Frequently asked questions

How long does fasting last before the test?
You’ll need to fast for 8 to 12 hours before the test. This means avoiding food and liquids (except water) from midnight the night before, unless your doctor specifies otherwise.
Can I take my diabetes medication before the test?
If you’re taking diabetes medication, check with your doctor first. Some medications may need to be adjusted or skipped before the test, depending on your specific treatment plan.
What if I feel dizzy or lightheaded before the test?
If you experience dizziness or lightheadedness, inform the healthcare provider before the test. They may provide you with a quick-sugar snack or adjust your fasting instructions to ensure your safety.
  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