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Fasting Plasma Glucose (Fasting Blood Glucose)

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 supports diabetes management or screening.

Quick summary

["A fasting glucose test helps detect high blood sugar, which may indicate diabetes or prediabetes."]

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

Key facts at a glance

LOINC
40285-9
Short code
Glucose 75M p Glc SerPl-sCnc
Synonyms
Glucose 75M p Glc SerPl-sCnc
Category
glucose
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
70
Ref high
100
Critical range
50 N/A – 400 N/A
Fasting
true
Population
adult
Sex
all
Age range
18–65 years
CPT
82947
SNOMED
260395008
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 routine check-ups, especially for people at higher risk of diabetes.

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. 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 analyzed to measure glucose concentration. The result helps determine if your blood sugar is within a healthy range or if further action is needed.

What the Results Mean

Results are typically reported in milligrams per deciliter (mg/dL). A reading below the reference range usually means your blood sugar is normal, while higher levels may signal potential issues like diabetes.

Reference range

Fasting: 70-100 mg/dLN/A

Specimen: serum

Fasting for 8-12 hours required. Water is permitted. Avoid chewing gum and smoking before the test.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Fasting Blood Sugar

Frequently asked questions

How often should I get this test?
Fasting glucose tests are often recommended annually for adults aged 45+ or those with risk factors (e.g., obesity, family history of diabetes). Your doctor may adjust frequency based on your health status.
Can I eat or drink anything before the test?
No, you must fast for 8–12 hours. Only water is allowed. Skipping this step can affect accuracy.
What if my blood sugar is high or low?
High results may prompt further testing (e.g., HbA1c) or lifestyle changes. Low results are less common but may require medical evaluation to rule out conditions like hypoglycemia.
  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