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Glucose, Plasma (Fasting) by Substance Concentration

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 identify risks for diabetes or other metabolic conditions.

Quick summary

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

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

Key facts at a glance

LOINC
101476-0
Short code
Glucose p fast BldV-sCnc
Synonyms
Glucose p fast BldV-sCnc
Category
glucose
Sample
whole-blood
Container
Lavender-top (EDTA)
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
3 mL
Stability
Room temperature: 4h, Refrigerated: 24h
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
4–24 hours
Order
routine

Why This Test Matters

Fasting means you shouldn’t eat or drink anything—except water—8 hours before your blood draw. This test is critical for diagnosing conditions like type 2 diabetes, where your body struggles to regulate blood sugar properly.

What to Expect During the Test

You’ll have a small needle inserted into your arm to draw blood from a vein. The process is quick and usually painless. Afterward, you can resume eating and drinking normally.

When You Might Need This Test

Your doctor may order this test if you have symptoms like excessive thirst, frequent urination, unexplained weight changes, or if you’re at higher risk for diabetes (e.g., due to family history, obesity, or high blood pressure).

How the Results Are Used

Your results help your healthcare provider determine if your blood sugar is within a healthy range or if you need lifestyle changes, medications, or further testing.

Reference range

Adult: 10-40 U/LN/A

Specimen: whole-blood

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.

Clinical Significance: Glucose Levels and Health

Short name

Fasting Plasma Glucose

Frequently asked questions

How long does it take to get my results?
Results are typically available within 1–3 business days, depending on your lab. Your doctor will discuss them with you during your follow-up visit.
What does a high or low fasting glucose level mean?
A high fasting glucose level may indicate diabetes or insulin resistance, while very low levels could signal hypoglycemia (low blood sugar), especially if you’re on diabetes medications or insulin.
Can I eat before my test if I’m not fasting?
No, fasting is required for this test. If you miss the fasting window, your results may not be accurate, and your doctor may need to reschedule.
  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