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Glucose in Serum (Fasting) – Quantitative Measurement

Published: August 9, 2026Updated: August 16, 2026

This test measures your blood sugar level after you’ve gone without food for at least 8 hours. It helps your doctor check for diabetes, high blood sugar, or other metabolic conditions.

Quick summary

["A fasting glucose test helps assess your blood sugar control and identify potential diabetes or metabolic disorders."]

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

Key facts at a glance

LOINC
48076-4
Short code
GH 2.5h p Gc SerPl-aCnc
Synonyms
GH 2.5h p Gc SerPl-aCnc
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 during pregnancy (gestational diabetes screening) or if you have a family history of diabetes.

How the Test Works

A blood sample is taken from a vein in your arm. The lab analyzes a small amount of your serum (liquid part of blood after clotting) to measure glucose concentration using a highly sensitive method.

What to Expect Before the Test

You’ll need to fast (no food or drink except water) for 8–12 hours before the test. Avoid caffeine or sugary drinks. Let your doctor know about any medications you’re taking, as some may affect results.

What to Expect During the Test

You’ll sit comfortably while a healthcare provider inserts a small needle into your arm. A small amount of blood is drawn into a test tube. The process usually takes a few minutes, and you may feel a brief pinch or sting.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Fasting Serum Glucose

Frequently asked questions

High fasting glucose levels (above normal ranges) may indicate diabetes, prediabetes, or insulin resistance. Consistently low levels could suggest hormonal imbalances or other conditions requiring medical evaluation.
This test is a key part of routine health checks, especially for older adults or those with risk factors like obesity, high blood pressure, or a sedentary lifestyle.
How long will I need to fast for this test?
You’ll need to fast for at least 8 hours before the test, with water allowed. Some labs may specify a longer fast (10–12 hours) for more accurate results.
Can I take my usual medications on fasting day?
If your doctor prescribes medications for essential conditions (e.g., blood pressure, diabetes), ask if you should take them on fasting day. Otherwise, skip them unless instructed otherwise.
  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