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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 a set period, helping your healthcare provider check for diabetes or other blood sugar issues.

Quick summary

["A fasting blood sugar test helps assess your risk for diabetes or metabolic problems."]

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

Key facts at a glance

LOINC
46412-3
Short code
GH 105M p Arg SerPl-mCnc
Synonyms
GH 105M p Arg SerPl-mCnc
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
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 used to monitor blood sugar levels in people with diabetes or prediabetes.

What to Expect Before the Test

You’ll need to fast for 8–12 hours before the test, meaning no food or drink (except water) after midnight. Bring your fasting schedule with you to confirm.

How the Test Works

A healthcare provider will draw blood from a vein in your arm. The sample is sent to a lab to measure glucose concentration in your serum.

What the Results Mean

Results are compared to standard reference ranges to identify abnormal levels. High or low readings may signal conditions like diabetes, hypoglycemia, or other metabolic disorders.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

This test is critical for diagnosing and managing diabetes, detecting prediabetes, and evaluating conditions affecting blood sugar regulation. It helps prevent long-term complications like nerve damage or heart disease.

Short name

Fasting Serum Glucose

Frequently asked questions

Will I feel any pain or discomfort during the test?
You may feel a slight pinch or sting when the needle is inserted, but it usually goes away quickly. Most people don’t feel pain afterward.
How long will I need to fast before the test?
Follow your doctor’s instructions, typically 8–12 hours of fasting (no food or liquids except water) before the test.
Can I take my diabetes medications on the day of the test?
Check with your doctor first, as some medications may affect your fasting blood sugar results. Never stop taking them without approval.
  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