Soluble C5b-9 Assay

The complement system consists of three initiating pathways – the classical, alternative and lectin – activation of which leads to the generation of C3 and C5 convertases. The latter initiates the sequential activation of the terminal pathway (C5 to C9) resulting in the formation of pore-forming membrane attack complex C5b–9 (MAC), a stable complex that mediates irreversible cell lysis. Fluid-phase C5b-9 complexes (soluble C5b-9) may also form in complex with regulatory proteins like protein S.

C3 Glomerulopathy (C3G):  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. Soluble C5b-9 is elevated in both DDD and C3GN, but only the difference between C3GN and controls reaches statistical significance (p<0.001 for only C3GN) (see Zhang et al., Defining the complement biomarker profile of C3 glomerulopathy, CJASN 2014).

Atypical Hemolytic Uremic Syndrome:  Soluble C5b-9 levels are elevated in the majority of patients with active atypical hemolytic uremic syndrome but less frequently when the disease is in remission.  Soluble C5b-9 may be useful as a biomarker to monitor activity of terminal pathway of complement (Bu et al., Soluble C5b-9 as a biomarker for complement activation in atypical hemolytic uremic syndrome, AJKD 2015).

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.