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Test Code C4 C4 Complement, Antigen, Serum or Plasma

Additional Codes

Epic Order Code: LAB151
Sunquest Order Code: C4

Specimen Required

Container Type:


Inpatient: Mint

STAT: Mint

Outpatient: Gold

Acceptable: Red Top or Green Lithium Heparin.


Optimal Collection Volume: 

4.5 mL; Full Tube

Collection Instructions:

Gently invert sample 5-6 times after collection.

Processing Instructions: 

1. Allow serum sample to clot for 30 minutes.

2. Centrifuge specimen within 2 hours of collection.

3. Specimen tubes without a gel barrier should have the serum or plasma aliquoted to a false bottom container after centrifugation.

4. Keep serum/plasma refrigerated until testing can be performed.

Useful For

This assay is useful in assessing disease activity in a number of inflammatory processes such as systemic lupus erythematosus (SLE), proliferative glomerulonephritis, or rheumatoid arthritis.

Method Name

Immunoturbidimetric assay

Stability Information

Specimen Type Temperature Time
Serum* Refrigerated 8 days
  Ambient  2 days
  Frozen  3 months

*Note: Heparinized plasma in gel separator tubes is less stable than serum and is only suitable for add-on testing up to 2 days following sample collection. 

Rejection Due To

Hemolysis Mild OK; Moderate OK; Gross Reject
Lipemia Mild OK; Moderate OK; Gross Reject
Icterus Mild OK; Moderate OK; Gross Reject
Other N/A


Post Processing Specimen Type

Preferred: Serum

Alternate: Plasma

Specimen Minimum Volume

Collecting minimum volumes can result in a need for sample recollection, and/or a delay in results. Minimum volumes are subjective and cannot account for all aspects of specimen and testing needs. Refer to the Specimen Required section for optimal volumes for laboratory specimens. Contact the Bronson Laboratory if complex collection exceptions occur that require more information.


Minimum Volume: 0.5 mL whole blood, 0.25 mL serum or plasma
Neonate Volume: 1 microtainer (400-600 uL)

Performing Laboratory

Bronson Laboratory, Chemistry - Kalamazoo

Day(s) Performed


Reference Values

 Test ID   Reference Range    Units      
C4 10-40 mg/dL

LOINC Code Information


CPT Code Information


Sample Retention Time

7 days