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Test ID: 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

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.


C4 levels will be decreased in acquired autoimmune disorders, in 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

Report Available

1 to 2 days

Day(s) Performed

Monday through Friday

Clinical Reference

1. Ross SC, Densen P: Complement deficiency states and infection: epidemiology, pathogenesis, and consequences of neisserial and other infections in an immune deficiency. Medicine 1984;63:243-273

2. Frank MM: Complement in the pathophysiology of human disease. N Engl J Med 1987;316:1525-1530

3. Tiffany TO: Fluorometry, nephelometry, and turbidimetry. In Textbook of Clinical Chemistry. Edited by NW Tietz. Philadelphia, WB Saunders Company, 1986, pp 79-97

Method Name


Specimen Type


Specimen Required


Preferred: Serum gel

Acceptable: Red top

Specimen Volume: 1 mL

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


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


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

Mayo Clinic Laboratories | Neurology Catalog Additional Information:

mml-Cerebrovascular, mml-Headache, mml-Demyelinating-Diseases, mml-Neuroimmunology, mml-Neuromuscular, mml-Pediatric, mml-Spinal-Cord