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Glucose in Serum (Fasting)

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

This test measures your blood sugar level after you’ve fasted for 8–12 hours. It helps assess your blood sugar control and identify conditions like diabetes or prediabetes.

Quick summary

["A fasting blood sugar test checks if your body processes glucose normally."]

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

Key facts at a glance

LOINC
33104-1
Short code
GA from GSD.Daya91
Synonyms
GA from GSD.Daya91
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
us-estimated-from-gsd-daya
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 This Test Matters

Your doctor may order this test to diagnose or monitor diabetes, check for high blood sugar, or evaluate how your body responds to medications. It’s also used in screening for conditions like hypoglycemia (low blood sugar) or metabolic disorders.

What to Expect Before the Test

You’ll need to fast (no food or drink except water) for 8–12 hours before the test. Avoid smoking, caffeine, or strenuous activity during this time. Bring your doctor’s instructions to confirm fasting guidelines.

How the Test Is Performed

A healthcare provider will draw blood from a vein in your arm using a small needle. You may feel a brief pinch, but the procedure is quick and usually painless. The blood sample is sent to a lab for analysis.

What the Results Mean

Results are compared to a reference range, but your doctor will interpret them based on your health history and other factors. High or low results may trigger further testing or lifestyle adjustments.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Fasting Serum Glucose

Frequently asked questions

What causes elevated or low fasting glucose?
Elevated fasting glucose is often linked to diabetes, insulin resistance, or poor diet. Low fasting glucose (hypoglycemia) can result from medications, certain foods, or metabolic issues. Both conditions may require medical attention to prevent complications.
How often should I get this test?
Frequency depends on your health status. People with diabetes typically check every 3–6 months, while others may need it less often. Follow your doctor’s recommendations for follow-up testing.
Can I eat or drink anything before the test?
No, you must fast for 8–12 hours before the test. Only water is allowed. Check with your doctor if you have questions about specific dietary restrictions.
  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