Fluid-Phase Activity Assay/ C3 Nephritic Factor/ C5 Nephritic Factor

Dense Deposit Disease (DDD, aka Membranoproliferative Glomerulonephritis Type II, MPGNII)
C3 nephritic factors (C3Nefs), C5 nephritic factors (C5Nefs) and fluid-phase activity assay (nef activity) are defined as IgG autoantibodies to C3 convertase (C3bBb) that were first described by Spitzer and colleagues in 1969 as a substance in patient serum that constantly activated the alternative pathway cascade (Spitzer, 1969). They can be detected in ~80% of DDD patients and interfere with innate mechanisms that would otherwise control C3 convertase activity. Nephritic factors can also be detected in patients with partial lipodystrophy, meningococcal meningitis and post-streptococcal acute glomerulonephritis (Savage et al., 2009; Fremeaux-Bacchi, et al., 1994; Hulton, et al., 1992).

Indications for screening
Screening is appropriate for patients with biopsy-proven DDD.

MORL screening methodology
Three different methods are used to detect Nephritic Factors.

  1. Fluid-Phase Activity Assay - Immunofixation electrophoresis (IFE) combines the techniques of electrophoresis with immunofixation to detect C3 degradation products, an indirect measure of dysregulation of C3 convertase. Conversion of C3 to C3c is quantitated (Koch, et al., 1981).
  2. C3Nef - C3 Convertase Stabilizing Assay (C3CSA) measures the ability of C3Nefs to stabilize C3 convertase on sheep erythrocytes. Stabilizing activities are reported as a function of hemolysis at 20 minutes.
  3. C5Nef - C3 Convertase Stabilizing Assay with Properdin (C3CSAP) measures the ability of C3Nefs to stabilize C3 convertase built with properdin on sheep erythrocytes. Stabilizing activities are reported as a function of hemolysis at 40 minutes.

Turnaround time
Turnaround time is ~4 weeks

Sample Required
1 ml frozen serum (please 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.


Fremeaux-Bacchi, V, et al.: Hypocomplementaemia of poststreptococcal acute glomerulonephritis is associated with C3 nephritic factor (C3NeF) IgG autoantibody activity. Nephrol Dial Trans. 1995; 10(9); 1782-3.
PubMed ID: 7708258

Hulton, SA, et al.: Mesangiocapillary glomerulonephritis associated with meningococcal meningitis, C3 nephritic factor and persistently low complement C3 and C5. Pediatr Nephrol. 1992 May; 6(3):239-43.
PubMed ID: 1616831

Koch FJ, et al.: Test for C3 nephritic factor activity by immunofixation electrophoresis. Am J Clin Pathol. 1981 Jul, 76(1):63-67.
PubMed ID: 6789671

Savage DB,  et al.: Complement abnormalities in acquired lipodystrophy revisited. J Clin Endocrinol Metab. 2009 Jan, 94(1); 10-6.
PubMed ID: 18854390

Spitzer RE, et al.: Serum C’3 lytic system in patients with glomerulonephritis. Science. 1969 Apr 25; 164(878); 436-7.
PubMed ID: 4180576