Complement C5 Level Assay

Complement component 5 (C5) is a plasma glycoprotein (MW: 195 kDa) synthesized in the liver, monocytes and lymphocytes. The mature protein is composed of two disulfide-bound polypeptide chains (C5α and C5β). Upon activation, C5 is cleaved into C5a (MW: 11 kDa) and C5b (MW: 185 kDa) by C5 convertase. C5a is a potent anaphylatoxin that facilitates acute inflammatory responses; C5b initiates the sequential activation of the terminal pathway (C6 to C9) resulting in formation of the terminal complement complex (C5b-9).

The common pathophysiological basis of both Dense Deposit Disease (DDD) and C3 Glomerulonephritis (C3GN) is dysregulation of the AP. Consumption of AP complement components is dependent on the degree of dysregulation of the C3 and C5 convertases. Plasma C5 levels are reduced in both DDD and C3GN as compared to controls (p<0.001 for both diseases) (see Zhang et al. Defining the complement biomarker profile of C3 glomerulopathy, CJASN 2014).

Indications for screening 
Screening is appropriate in patients with complement-mediated renal diseases.

MORL screening methodology 
Enzyme Linked Immuno-Sorbent Assay (ELISA)

Turnaround time 
Turnaround time is ~2 weeks

Sample Required 
1 ml frozen EDTA plasma (see testing requisition for specimen handling).

Cost & CPT Codes

The Clinical Diagnostics Service of the Molecular Otolaryngology & Renal Research Laboratories is a CLIA-approved, Joint Commission-accredited diagnostic laboratory.