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HelpTest Code C2FXN C2 Complement, Functional, Serum
Reporting Name
C2 Complement, Functional, S, NRUseful For
Investigation of a patient with a low (absent) hemolytic complement
Performing Laboratory
Mayo Clinic Laboratories in Rochester
Specimen Type
SerumOrdering Guidance
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.
To evaluate for complement C2, C3, and C4 in one orderable, consider ordering C2 / C2 Complement, Functional, with Reflex, Serum.
Specimen Required
Patient Preparation:
Fasting: 12 hours, preferred but not required
Supplies: Sarstedt Aliquot Tube, 5 mL (T914)
Collection Container/Tube:
Preferred: Serum gel
Acceptable: Red top
Submission Container/Tube: Plastic vial
Specimen Volume: 1 mL serum
Collection Instructions:
1. Immediately after specimen collection, place the tube on wet ice and allow specimen to clot.
2. Centrifuge at 4° C and aliquot serum into a plastic vial.
3. Within 30 minutes of centrifugation, freeze specimen. Specimen must be placed on dry ice if not frozen immediately.
Note: If a refrigerated centrifuge is not available, it is acceptable to use a room temperature centrifuge, provided the specimen is kept on ice before centrifugation, and immediately afterward, the serum aliquoted and frozen.
Specimen Minimum Volume
Serum: 0.5 mL
Specimen Stability Information
| Specimen Type | Temperature | Time |
|---|---|---|
| Serum | Frozen | 21 days |
Reference Values
≥34 U/mL
Day(s) Performed
Tuesday, Friday
Test Classification
This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. It 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 |
|---|---|---|
| C2FXN | C2 Complement, Functional, S, NR | 93977-7 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| C2FX | C2 Complement,Functional,S | 93977-7 |
| INT53 | Interpretation | 69048-7 |
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).
Absent (or low) C2 levels in the presence of normal C3 and C4 values are consistent with a C2 deficiency.
Low C2 levels in the presence of low C3 and C4 values are consistent with a complement-consumptive process.
Low C2 and C4 values, in the presence of normal values for C3 is suggestive of C1 esterase inhibitor deficiency.
Clinical Reference
1. Gaither TA, Frank MM. Complement. In: Henry JB, ed. Clinical Diagnosis and Management by Laboratory Methods. 17th ed. WB Saunders Company; 1984:879-892
2. Agnello V. Complement deficiency states. Medicine. 1978;57(1):1-23
3. Buckley D, Barnes L. Childhood subacute cutaneous lupus erythematosus associated with homozygous complement 2 deficiency. Pediatr Dermatol. 1995;12(4):327-330
4. Willrich MAV, Braun KMP, Moyer AM, Jeffrey DH, Frazer-Abel A. Complement testing in the clinical laboratory. Crit Rev Clin Lab Sci. 2021;58(7):447-478. doi:10.1080/10408363.2021.1907297
5. Nandakumar V, Braun KMP, Willrich MAV. Challenges for complement functional assays in the clinical laboratory: From test validation to clinical interpretation. J Immunol Methods 2025;537:113824
6. Moyer AM, Sridharan M, Willrich MA. Complement defects. In: Schmitz JL, Detrick B, O'Gorman MRG, eds. Manual of molecular and clinical laboratory immunology, Vol. 2. Wiley, 2024:796-812
Report Available
1 to 3 daysMethod Name
Turbidimetric Measurement of Liposome Lysis