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Serum or plasma mass concentration of complement component C3

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

This test measures the amount of C3 protein in your blood. C3 is part of your immune system and helps fight infections.

Quick summary

["C3 helps your immune system respond to infections and inflammation."]

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

Key facts at a glance

LOINC
30522-7
Short code
CRP SerPl HS-mCnc
Synonyms
CRP SerPl HS-mCnc
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
0
Ref high
3
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
high-sensitivity
CPT
86140
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

What Is C3?

C3 is a key protein in your complement system, which is a part of your immune response. It helps identify and destroy harmful substances, like bacteria and viruses, and signals other immune cells to take action. Low levels may suggest immune system issues or certain health conditions.

Why Might You Need This Test?

Your doctor may order a C3 test to check for problems with your immune system, such as infections, autoimmune diseases, or kidney issues. It can also help monitor conditions like lupus or other inflammatory disorders.

When Is This Test Done?

This test is usually done by taking a blood sample. The sample is sent to a lab where it is analyzed to measure the concentration of C3 protein.

What Does a Low or High Level Mean?

Results can vary based on your health and medical history. Low C3 levels may indicate immune system dysfunction, infections, or certain medications. High levels could be linked to inflammation or other conditions that stimulate the immune response.

Reference range

Normal: <3.0 mg/LN/A

Specimen: serum

For females: inform if menstrual cycle status. For certain tests, timing within menstrual cycle may matter.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance: C3 Levels and Health

Short name

C3 Protein Level

Frequently asked questions

What could cause abnormal C3 levels?
Abnormal C3 levels can be caused by infections (like pneumonia or sepsis), autoimmune diseases (such as lupus or rheumatoid arthritis), kidney problems, or certain medications that affect the immune system. Always discuss symptoms and test results with your healthcare provider.
How often should I get this test?
The frequency depends on your medical condition and treatment plan. Your doctor will determine how often you need retesting based on your specific situation.
Can I prepare for this test?
No special preparation is usually needed, but avoid heavy meals before the blood draw. Follow any specific instructions your doctor provides.
  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