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Glucose, 4-hour postprandial (serum/plasma)

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

This test measures the amount of glucose (sugar) in your blood 4 hours after eating.

Quick summary

["Helps assess how your body handles sugar after meals."]

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

Key facts at a glance

LOINC
21309-0
Short code
Glucose 45M p chal SerPl-mCnc
Synonyms
Glucose 45M p chal SerPl-mCnc
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 Is This Test Done?

Doctors may order this test to check for conditions like diabetes, prediabetes, or to monitor how well your body processes sugar, especially if you have symptoms like frequent hunger, fatigue, or unexplained weight changes. It can also help evaluate how well medications for diabetes are working.

What to Expect Before the Test

You’ll likely need to fast for 8–12 hours before this test, but the 4-hour postprandial sample is taken after you’ve eaten a meal. Bring any medications you’re taking with you. If you’re pregnant, have diabetes, or have other health conditions, let your doctor know before fasting.

How the Test Is Done

A healthcare provider will draw blood from a vein in your arm. You may feel a small pinch, but it usually doesn’t cause much discomfort. The blood sample is sent to a lab to measure glucose levels.

What the Results Mean

Results help determine if your blood sugar is too high or too low after eating, which can indicate how your body manages glucose. Your doctor will compare these results to your overall health and other tests to make a diagnosis or treatment plan.

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

Frequently asked questions

What does a 4-hour glucose test measure?
It measures your blood sugar level 4 hours after eating, giving insight into how your body processes sugar over time—useful for assessing diabetes or metabolic health.
Can I eat before this test?
No, you must fast for 8–12 hours before fasting tests, but the 4-hour sample is taken after you’ve eaten a meal. Follow your doctor’s instructions carefully.
How often should I get this test?
Your doctor will determine how often you need this test based on your health status, such as whether you have diabetes, prediabetes, or other related conditions. Regular monitoring may be recommended for ongoing management.
  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