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Test Code C1QFX C1q Complement, Functional, Serum

Reporting Name

C1Q Complement, Functional, S

Useful For

Diagnosis of C1 deficiency

 

Investigation of a patient with an absent total complement level

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Specimen Type

Serum Red


Ordering Guidance


The total complement (CH50) 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 CH50.



Specimen Required


Patient Preparation: Fasting preferred

Supplies: Sarstedt 5 mL Aliquot Tube (T914)

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

Reference Values

34-63 U/mL

Day(s) Performed

Monday through Friday

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 US Food and Drug Administration.

CPT Code Information

86161

LOINC Code Information

Test ID Test Order Name Order LOINC Value
C1QFX C1Q Complement, Functional, S 87722-5

 

Result ID Test Result Name Result LOINC Value
C1QFX C1Q Complement, Functional, S 87722-5

Clinical Information

Complement proteins are components of the innate immune system. There are 3 pathways to complement activation: 1) the classical pathway, 2) the alternative (or properdin) pathway, and 3) the lectin (or mannan binding lectin) pathway. The classical pathway of the complement system is composed of a series of proteins that are activated in response to the presence of immune complexes. A single IgM molecule or 2 IgG molecules are sufficient to trigger activation of the recognition complex initiated by C1q. The activation process triggers a cascade that includes an amplification loop. The amplification loop is mediated by C3, with cleavage of a series of proteins, and results in 3 main end products: 1) anaphylatoxins that promote inflammation (C3a, C5a), 2) opsonization peptides that are chemotactic for neutrophils (C3b) and facilitate phagocytosis, and 3) the membrane attack complex, which promotes cell lysis.

 

C1 is composed of 3 subunits designated as C1q, C1r, and C1s. C1q recognizes and binds to immunoglobulin complexed to antigen and initiates the complement cascade. Congenital deficiencies of any of the early complement components (C1-C4) result in an inability to generate the peptides that are necessary to clear immune complexes and to attract neutrophils or generate lytic activity. These patients have increased susceptibility to infections with encapsulated microorganisms. They may also have symptoms that suggest autoimmune disease in which complement deficiency may be an etiologic factor.

 

Inherited deficiency of C1 is rare. Just over 40 cases have been reported for C1q deficiency, and another 20 cases have been described for C1s and C1r deficiency. C1 deficiency is associated with increased incidence of immune complex disease (systemic lupus erythematosus [SLE], polymyositis, glomerulonephritis, and Henoch-Schonlein purpura), with SLE the most common manifestation of C1 deficiency. The SLE associated with C1 deficiency is similar to SLE without complement deficiency, but the age of onset is often prior to puberty.

 

Low C1 levels have also been reported in patients with abnormal immunoglobulin levels (Bruton and common variable hypogammaglobulinemia and severe combined immunodeficiency), and this is most likely due to increased catabolism.

 

Complement levels can be detected by antigen assays that quantitate the amount of the protein. For most of the complement proteins a small number of cases have been described in which the protein is present but is nonfunctional. These rare cases require a functional assay to detect the deficiency.

Interpretation

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).

 

The measurement of C1q activity is an indicator of the amount of C1 present. Absent C1q levels in the presence of normal C3 and C4 values are consistent with a C1 deficiency. Low C1q levels in the presence of low C4 but normal C3 may indicate the presence of an acquired inhibitor (autoantibody) to C1 esterase inhibitor.

Cautions

Absent (or low) C1q functional levels in the presence of normal C1q antigen levels should be replicated with a new serum specimen to confirm that C1q inactivation did not occur during shipping.

Report Available

2 to 4 days

Reject Due To

Gross hemolysis OK
Gross lipemia Reject
Gross icterus OK

Method Name

Automated Liposome Lysis Assay