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Test Code C4 Complement C4, Serum

Reporting Name

Complement C4, S

Useful For

Investigating an undetectable total complement (CH50)

 

Confirming hereditary angioedema (with low C1 inhibitor)

 

Assessing disease activity in systemic lupus erythematosus, proliferative glomerulonephritis, rheumatoid arthritis, and autoimmune hemolytic anemia

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Specimen Type

Serum


Specimen Required


Collection Container/Tube:

Preferred: Serum gel

Acceptable: Red top

Submission Container/Tube: Plastic vial

Specimen Volume: 1 mL

Collection Instructions: Centrifuge and aliquot serum into a plastic vial.


Specimen Minimum Volume

0.5 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Serum Refrigerated (preferred) 7 days
  Frozen  28 days
  Ambient  72 hours

Reference Values

14-40 mg/dL

Test Classification

This test has been cleared, approved, or is exempt by the US Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.

CPT Code Information

86160

LOINC Code Information

Test ID Test Order Name Order LOINC Value
C4 Complement C4, S 4498-2

 

Result ID Test Result Name Result LOINC Value
C4 Complement C4, S 4498-2

Clinical Information

The complement system is an integral part of the immune defenses. It can be activated via immune complexes (classic pathway) or by bacterial polysaccharides (alternative pathway). The classic complement pathway consists of recognition, (C1q, C1r, C1s), activation (C2, C3, C4), and attack (C5, C6, C7, C8, C9) mechanisms with respect to their role in antibody-mediated cytolysis. C4 is one of the activation proteins of the classic pathway.

 

In the absence of C4, immune complexes will not be cleared by C3 activation peptides, but bacterial infections can still be defended via the alternative pathway.

 

C4 may be decreased in systemic lupus erythematosus, early glomerulonephritis, immune complex disease, cryoglobulinemia, hereditary angioedema, and congenital C4 deficiency.

Interpretation

C4 levels will be decreased in acquired autoimmune disorders, in the active phase of lupus erythematosus, and in rheumatoid arthritis.

 

An undetectable C4 level (with normal C3) suggests a congenital C4 deficiency.

 

Levels will be increased in patients with autoimmune hemolytic anemia.

Cautions

The results are dependent on appropriate specimen transport.

Clinical Reference

1. Willrich MAV, Braun KMP, Moyer AM, Jeffrey DH, Frazer-Abel A: Complement testing in the clinical laboratory. Crit Rev Clin Lab Sci. 2021 Nov;58(7):447-478. doi: 10.1080/10408363.2021.19072972

2. Wong EKS, Kavanagh D: Diseases of complement dysregulation-an overview. Semin Immunopathol. 2018 Jan;40(1):49-64. doi: 10.1007/s00281-017-0663-8

3. Prohaszka Z, Kirschfink M, Frazer-Abel A: Complement analysis in the era of targeted therapeutics. Mol Immunol. 2018 Oct;102:84-88. doi: 10.1016/j.molimm.2018.06.001

4. Brodszki N, Frazer-Abel A, Grumach AS, et al: European Society for Immunodeficiencies (ESID) and European Reference Network on Rare Primary Immunodeficiency, Autoinflammatory and Autoimmune Diseases (ERN RITA) Complement Guideline: Deficiencies, Diagnosis, and Management. J Clin Immunol. 2020 May;40(4):576-591. doi: 10.1007/s10875-020-00754-1

Method Description

C4 is measured by immunonephelometry. Antiserum to C4 is mixed with patient serum, the light scatter resulting from the antibody interaction with C4 is measured, and the signal is compared to standard concentrations of C4.(Instruction manual: Siemens Nephelometer II Operations. Siemens, Inc; Version 2.4, 07/2019; Addendum to the Instruction Manual 2.3, 08/2017)

Reject Due To

Gross hemolysis OK
Gross lipemia Reject
Gross icterus OK

Method Name

Nephelometry

Secondary ID

8171

Specimen Retention Time

14 days

Forms

If not ordering electronically, complete, print, and send a Renal Diagnostics Test Request (T830) with the specimen.

Day(s) Performed

Monday through Friday

Report Available

1 to 2 days