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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 how well your body uses sugar for energy.

Quick summary

["A fasting glucose test helps diagnose diabetes or prediabetes and assess blood sugar control."]

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

Key facts at a glance

LOINC
109396-2
Short code
GT1b Ganlg IgG Msmt Ser
Synonyms
GT1b Ganlg IgG Msmt Ser
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
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 This Test Is Done

Your doctor may order this test if you have symptoms like excessive thirst, frequent urination, unexplained weight loss, or fatigue. It’s also used during routine check-ups, especially for people at higher risk of diabetes, such as those with a family history or obesity.

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 to Expect During the Test

The process is quick and usually painless. You may feel a slight pinch or sting when the needle is inserted, but the blood sample is collected quickly. The site will be cleaned and bandaged afterward.

What the Results Mean

Results are interpreted by your doctor based on your medical history and other tests. High levels may indicate diabetes or insulin resistance, while low levels could signal conditions like hypoglycemia or poor absorption of nutrients.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Fasting serum glucose is a critical marker for diagnosing type 1 and type 2 diabetes. Elevated levels over time can damage blood vessels and nerves, leading to serious complications like heart disease, kidney problems, or nerve damage. Regular monitoring helps manage blood sugar and prevent long-term health issues.

Short name

Fasting Serum Glucose

Frequently asked questions

How long does it take to get my results?
Results are typically available within 1 to 3 business days, depending on your lab’s processing time. Your doctor will contact you with the final report once reviewed.
Can I eat or drink anything before the test?
No, you must fast for 8 to 12 hours before the test, excluding water. Avoid caffeine or sugary drinks to ensure accurate results.
Will I experience any side effects from the blood draw?
Most people experience only minor discomfort or bruising at the injection site. Rarely, there may be slight swelling or pain, but these usually resolve quickly.
  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