Skip to content

Glucose in Serum (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 your doctor check for diabetes or other blood sugar issues.

Quick summary

["A fasting blood sugar test helps assess whether your body processes sugar normally."]

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

Key facts at a glance

LOINC
11935-4
Short code
GA from HL
Synonyms
GA from HL
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-hl
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 if you have symptoms like excessive thirst, frequent urination, unexplained weight changes, or fatigue. It’s also part of routine check-ups for people at higher risk of diabetes.

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 doctor or lab technician will draw blood from a vein, usually in your arm.

What the Results Mean

Results are typically reported in milligrams per deciliter (mg/dL). A reading above a certain threshold may indicate prediabetes or diabetes, prompting further evaluation.

Common Reasons for Testing

Doctors may check fasting glucose levels if you have symptoms of high blood sugar, a family history of diabetes, or during pregnancy (gestational diabetes screening).

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

This test is critical for diagnosing conditions like type 1 or type 2 diabetes, prediabetes, or hypoglycemia (low blood sugar). Abnormal results may guide treatment plans, such as lifestyle changes or medication.

Short name

Fasting Serum Glucose

Frequently asked questions

What happens if my fasting blood sugar is high?
A high fasting glucose level may mean you have prediabetes or diabetes. Your doctor will likely recommend follow-up tests, such as an oral glucose tolerance test, to confirm and plan next steps.
Can I eat or drink anything before the test?
No, you must fast for 8 to 12 hours before the test. Only water is allowed. Avoid caffeine or sugary drinks, as they can affect results.
How long will it take to get my results?
Results are usually available within 1 to 3 business days, depending on your lab. Your doctor will discuss them with you during your follow-up visit.
  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