Ordering Recommendation

Follow-up test for complement activity screening when CH50 is low or absent and AH50 is normal and high suspicion remains for complement deficiency.

New York DOH Approval Status

This test is New York state approved.

Specimen Required

Patient Preparation

Serum separator tube.

Specimen Preparation

Allow specimen to clot for one hour at room temperature. Separate serum from cells ASAP or within 2 hours of collection. Transfer 1 mL serum to an ARUP Standard Transport Tube and freeze immediately. (Min: 0.3 mL)

Storage/Transport Temperature

CRITICAL FROZEN. Separate specimens must be submitted when multiple tests are ordered.

Unacceptable Conditions

Non-frozen specimens. Specimens exposed to repeated freeze/thaw cycles. Specimens left to clot at refrigerated temperature.


After separation from cells: Ambient: 2 hours; Refrigerated: Unacceptable; Frozen: 2 weeks


Quantitative Radial Immunodiffusion


Mon, Thu


5-10 days

Reference Interval

Effective May 21, 2018
1.6-4.0 mg/dL

Interpretive Data

Decreased C2 levels may be associated with increased susceptibility to infection (especially pneumococcal infections), systemic lupus erythematosus-like disease, rashes, arthritis, nephritis, and with C1-Esterase deficiency.  Increased C2 levels are associated with the acute phase response.

This test was developed and its performance characteristics determined by ARUP Laboratories. It has not been cleared or approved by the US Food and Drug Administration. This test was performed in a CLIA certified laboratory and is intended for clinical purposes.

Compliance Category

Laboratory Developed Test (LDT)


Hotline History


CPT Codes



Component Test Code* Component Chart Name LOINC
0050148 Complement Component 2 4484-2
* Component test codes cannot be used to order tests. The information provided here is not sufficient for interface builds; for a complete test mix, please click the sidebar link to access the Interface Map.


  • C2
  • C2 Antigen
  • C2 Level
  • Classical Pathway - Complement
  • complement classical pathway
  • Second componenet of complement
Complement Component 2