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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 to 12 hours. It helps assess how well your body uses glucose for energy.

Quick summary

["A fasting glucose test checks your blood sugar levels when you’re not eating, helping detect diabetes or other metabolic conditions."]

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

Key facts at a glance

LOINC
68942-2
Short code
GH 130M p Exc SerPl-mCnc
Synonyms
GH 130M p Exc 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 to diagnose or monitor conditions like diabetes, prediabetes, or to check for signs of high blood sugar. It’s also used before certain treatments or surgeries to ensure stable blood sugar levels.

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.

How the Test Works

A small sample of your blood is taken and sent to a lab. The lab measures the amount of glucose (sugar) in your serum using a specialized method, often an enzymatic assay.

What the Results Mean

Results are typically reported in milligrams per deciliter (mg/dL). High levels may indicate diabetes or insulin resistance, while very low levels could signal hypoglycemia or other issues.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance: Fasting Serum Glucose is critical for diagnosing diabetes (fasting glucose ≥126 mg/dL on two separate tests) and monitoring metabolic health. Abnormal results may prompt further testing or lifestyle changes.

Short name

Fasting Serum Glucose

Frequently asked questions

What causes fasting serum glucose levels to be high?
High fasting glucose levels can result from diabetes, insulin resistance, certain medications (like steroids), chronic stress, or poor diet. Lifestyle factors like obesity or physical inactivity may also play a role.
What should I do if my fasting glucose test is abnormal?
If your results are outside the expected range, your doctor may recommend follow-up tests (like an oral glucose tolerance test) or adjustments to diet, exercise, or medications. They’ll guide you on next steps based on your overall health.
Can I eat or drink anything before my fasting serum glucose test?
No, you must fast for 8 to 12 hours before the test. Only water is allowed. Avoid caffeine, alcohol, or sugary drinks during this time.
  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