Description
C3 Nephritic factor is an autoantibody found in some patients with mesangiocapillary glomerulonephritis, dense deposit disease and/or partial lipodistrophy. This most common form of this autoantibody recognises (and stabilises) the otherwise unstable C3 cleaving enzyme of the alternative pathway of the complement system. Presence of the autoantibody leads to uncontrolled activation of C3 leading to very low C3 levels but normal C4. The presence of this complement profile (very low C3 normal C4) in patients with appropriate renal symptoms is almost characteristic of the presence of C3 Nef. Specific tests for C3 Nef are problematic and rarely necessary. They involve adding a suspected sample with normal serum and measuriung loss of functional C3.
Indication
Mesangiocapillary glomerulonephritis and/or partial lipodistrophy should be considered only if C3 concentration below normal and C4 within reference range.
Interpretation
If positive in patients with renal disease it strongly suggests mesangio-capillary nephritis.
Sample
Serum Separator Tube (SST)
Assay details
Test serum incubated with normal serum for 30 minutes at 37°C. The degree of C3 activation is detected by electrophoresis.
Restrictions
Referred Test. Sample must be received in laboratory within 3 hrs of venepuncture.
Reference range
Negative/Positive
Assay range notes
Positive results expressed as 1 to 3+
Turnaround time
28 days
Analysing laboratory
Sheffield PRU