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Test Code C4FX C4 Complement, Functional, Serum

Reporting Name

C4 Complement, Functional, S

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Useful For

Diagnosis of C4 deficiency


Investigation of a patient with an undetectable total complement (CH50) level

Method Name

Automated Liposome Lysis Assay

Specimen Type

Serum Red

Advisory Information

The total complement assay (COM / Complement, Total, Serum) should be used as a screen for suspected complement deficiencies before ordering individual complement component assays. A deficiency of an individual component of the complement cascade will result in an undetectable total complement level.

Specimen Required

Patient Preparation: Fasting preferred

Supplies: Aliquot Tube, 5 mL (T465)

Collection Container/Tube: Red top

Submission Container/Tube: Plastic vial

Specimen Volume: 1 mL

Collection Instructions:

1. Immediately after specimen collection, place the tube on wet ice.

2. Centrifuge and aliquot serum into plastic vial.

3. Immediately freeze specimen.

Specimen Minimum Volume

0.5 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Serum Red Frozen 14 days

Reject Due To

Gross hemolysis OK
Gross lipemia Reject
Gross icterus OK

Reference Values

22-45 U/mL


Low levels of complement may be due to inherited deficiencies, acquired deficiencies, or due to complement consumption (eg, as a consequence of infectious or autoimmune processes).


Absent component 4 (C4) levels in the presence of normal C3 and C2 values are consistent with a C4 deficiency.


Normal results indicate both normal C4 protein levels and normal functional activity.


In hereditary angioedema, a disorder caused by C1 esterase inhibitor deficiency, absent or low C4 and C2 values are seen in the presence of normal C3 (due to activation and consumption of C4 and C2).

Day(s) and Time(s) Performed

Monday through Friday; 3 p.m.

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
C4FX C4 Complement, Functional, S 93978-5


Result ID Test Result Name Result LOINC Value
C4FX C4 Complement, Functional, S 93978-5