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Serum or plasma concentration of a substance related to immune response (e.g., complement factor C4)

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

This test measures the amount of a protein in your blood that plays a key role in your immune system. It helps check for conditions affecting your immune function.

Quick summary

["This test helps diagnose and monitor immune-related disorders."]

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

Key facts at a glance

LOINC
38915-5
Short code
Zic4 Ab Ser Ql
Synonyms
Zic4 Ab Ser Ql
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 Is This Test Done?

Your doctor may order this test to evaluate symptoms like frequent infections, swelling, or autoimmune conditions. It can also help monitor treatment for diseases like lupus or other immune disorders.

What Does the Test Involve?

You’ll provide a blood sample, either from a vein (usually in your arm) or a fingerstick. The lab then analyzes the sample to measure the protein level.

What Are Common Conditions Monitored?

High levels may suggest certain immune system responses or reactions to medications, while low levels can indicate autoimmune diseases, infections, or kidney problems.

What Should You Know Before Testing?

Avoid certain medications (like steroids) that may affect protein levels for a few days before testing. Fast for 8–12 hours if instructed.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

C4 Protein Level

Frequently asked questions

What does a low or high C4 protein level mean?
Low levels may signal immune system overactivity (e.g., autoimmune diseases) or kidney issues. High levels could indicate a temporary immune response or certain medications. Your doctor will interpret results in the context of your symptoms and other tests.
Do I need to fast before this test?
Check with your doctor—some tests require fasting, but others do not. Follow their instructions to ensure accurate results.
How long will I have to wait for 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.
  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