Complement Ba Fragment Assay

Dense Deposit Disease and C3 Glomerulonephritis 
Alternative pathway complement activation generates the active complement breakdown fragment Ba. In the presence of C3b, Factor B (MW: 93 kDa) binds to C3b to form the pre-convertase (C3bB). Factor D cleaves FB, generating the Ba fragment (MW: 33 kDa) and the proteolytic enzyme Bb (MW: 66 kDa). Bb is the catalytically active site of the C3bBb complex (C3 convertase) and is capable of cleaving new C3 to C3a and C3b. C3bBb also recruits available C3b to form the C5 convertase (C3bBbC3b) launching terminal pathway activation. The plasma concentration of Ba is reflective of this activity.

The common pathophysiological basis of both Dense Deposit Disease (DDD) and C3 Glomerulonephritis (C3GN) is dysregulation of the AP complement cascade. Consumption of AP complement components is dependent on the degree of dysregulation of the C3 and C5 convertases. Plasma levels of Ba are elevated in both DDD and C3GN as compared to controls (p<0.001), consistent with consumption of C3 in both diseases.

Indications for screening 
Screening is appropriate for patients with DDD and C3GN.

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
See the MORL testing menu
PDF icon Clinical Kidney Testing Requisition Form

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