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Glucose, Plasma (Fasting)

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

This test measures the amount of glucose (sugar) in your blood after you’ve fasted for at least 8 hours. It helps assess your blood sugar levels and supports diabetes screening or monitoring.

Quick summary

["A fasting plasma glucose test helps check for high blood sugar, which can indicate diabetes or prediabetes."]

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

Key facts at a glance

LOINC
63382-6
Short code
Glucose p fast Ur-mCnc
Synonyms
Glucose p fast Ur-mCnc
Category
glucose
Sample
urine
Container
Sterile urine container
Units
N/A
Ref low
10
Ref high
40
Critical range
50 N/A – 400 N/A
Fasting
true
Population
adult
Sex
all
Age range
18–65 years
CPT
84484
SNOMED
302774002
Specimen volume
10 mL
Stability
Room temperature: 2h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
4–24 hours
Order
routine

Why Is This Test Done?

Your healthcare provider may order this test to diagnose or monitor conditions like diabetes, prediabetes, or metabolic disorders. It’s also used during pregnancy to check for gestational diabetes or other blood sugar-related risks.

What to Expect Before the Test

You’ll need to fast (not eat or drink anything except water) for at least 8 hours before the test. Your blood will be drawn from a vein, usually in your arm, by a phlebotomist.

What Happens During the Test?

A small needle will be inserted into your arm to collect a blood sample. The process is quick and typically painless. The blood is then sent to a lab for analysis.

What Are the Results?

Results are usually reported in milligrams per deciliter (mg/dL). Your provider will interpret the results in relation to your medical history and symptoms.

Reference range

Adult: 10-40 U/LN/A

Specimen: urine

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.

High fasting plasma glucose levels (above normal ranges) may signal diabetes or insulin resistance. Repeatedly low levels (rare) could indicate conditions like hypoglycemia or hormonal imbalances. Regular monitoring helps manage blood sugar and prevent long-term complications.

Short name

Fasting Plasma Glucose

Frequently asked questions

What causes fasting plasma glucose to be abnormal?
Fasting plasma glucose can be affected by undiagnosed diabetes, insulin resistance, certain medications (like steroids), infections, stress, or poor nutrition. Genetics, obesity, or physical inactivity may also play a role.
How can I prepare for this test correctly?
Follow your provider’s instructions strictly: fast for at least 8 hours before testing, avoid alcohol, and don’t smoke. Wear comfortable clothing if you’ll need to sit or lie down during blood draw.
What if I have questions about my results?
Ask your healthcare provider to explain your results in detail. They can help clarify any concerns, especially if you have symptoms like fatigue, frequent urination, or blurred vision, which may relate to blood sugar levels.
  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