C2 Complement, Functional with Reflex, Serum

Test Mnemonic


CPT Codes

  • 86161 - QTY (1)


  • C2 Functional


  • Complement C2
  • Complement C3, if indicated
  • Complement C4, if indicated

Performing Laboratory

Mayo Clinic Dpt of Lab Med & Pathology

Specimen Requirements

Volume Type Container Collect Temperature Transport Temperature Special Instructions
1 mL No additive (Red) FrozenFasting preferred. Place tube on wet ice immediately after collection. Spin, separate from clot and FREEZE serum immediately.

Minimum Specimen Requirements

Volume Type Container Collect Temperature Transport Temperature Special Instructions
0.5 mL     


Environmental Condition Description
Frozen21 days
AmbientNot acceptable
RefrigeratedNot acceptable

Days Performed

Mon - Sat

Turnaround Time

2 - 3 days


Name Description
C2H(50) Automated Liposome Lysis Assay 

Reference Range

C2 Complement Functional, w/Rflx
Sex Age From Age To Type Range Range Unit
   Years99 YearsNormal25 - 47U/mL

Special Info

Testing Algorithm: If the C2 result is < 15 U/mL, then C3 and C4 will be performed at an additional cost. Grossly lipemic specimens are unacceptable. Serum gel tubes will be rejected.

Clinical Info

The classic pathway of the complement system is composed of a series of proteins that are activated in response to the presence of immune complexes. This activation process results in the formation of the lytic membrane attack complex, as well as the generation of activation peptides that are chemotactic for neutrophils and that bind to immune complexes and complement receptors. The absence of early components (C1, C2, C4) of the complement cascade results in the inability of immune complexes to activate the cascade. Patients with deficiencies of the early complement proteins are unable to generate lytic activity or to clear immune complexes. Although rare, C2 deficiency is the most common inherited complement deficiency. Homozygous C2 deficiency has an estimated prevalence ranging from 1 in 10,000 to 1 in 40,000. Half of the homozygous patients are clinically normal. However, discoid lupus erythematosus or systemic lupus erythematosus (SLE) occurs in approximately one-third of patients with homozygous C2 deficiency. Patients with SLE and a C2 deficiency frequently have a normal anti-ds DNA titer. Clinically, many have lupus-like skin lesions and photosensitivity, but immunofluorescence studies may fail to demonstrate immunoglobulin or complement along the epidermal-dermal junction. Other diseases reported to be associated with C2 deficiency include dermatomyositis, glomerulonephritis, vasculitis, atrophodema, cold urticaria, inflammatory bowel disease, and recurrent infections. The laboratory findings that suggest C2 deficiency include a hemolytic complement (CH50) of nearly zero, with normal values for C3 and C4.