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 8–12 hours. It helps assess your blood sugar levels and overall risk for diabetes or other metabolic conditions.

Quick summary

["A fasting glucose test checks your blood sugar baseline to detect diabetes or prediabetes early."]

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

Key facts at a glance

LOINC
56981-4
Short code
GH 30M p resting SerPl-mCnc
Synonyms
GH 30M p resting 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 if they suspect diabetes, prediabetes, or another blood sugar-related condition. It’s also part of routine check-ups for people at higher risk.

What to Expect Before the Test

You’ll need to fast (not eat or drink anything except water) for 8–12 hours before the test. Avoid sugary drinks, coffee, or alcohol. Your blood will be drawn from a vein in your arm, similar to other blood tests.

What Happens During the Test

A healthcare professional will insert a small needle into your arm to collect a blood sample. You may feel a slight pinch, but it’s usually over quickly. The blood is sent to a lab for analysis.

What the Results Mean

Results are typically reported in milligrams per deciliter (mg/dL). A normal result is usually below a certain threshold, but your doctor will interpret it based on your health history and symptoms. High levels may indicate diabetes or insulin resistance, while very low levels could signal other conditions.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Fasting Serum Glucose

Frequently asked questions

How often should I get this test?
The frequency depends on your health status. If you have diabetes or are at risk, your doctor may recommend testing every 1–3 years or more often if needed. If you’re healthy, it’s usually part of a general health screening every few years.
What can affect my fasting glucose test results?
Skipping the fasting period, eating or drinking anything before the test, stress, illness, or certain medications can affect results. If you’re unsure, ask your doctor or lab technician for guidance.
Do I need to prepare differently if I’m pregnant?
Yes, if you’re pregnant, you may need to adjust fasting times or timing around meals. Always follow your healthcare provider’s specific instructions to ensure accurate results.
  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