Special Precautions/Comments:

Interferences: None known.

Additional Information:

Indication: Investigation of unexplained low C3. Low C3 mandatory for this test.

Background Information: C3 nephritic factor is an IgG autoantibody which binds to the Bb portion of C3 convertase (C3bBb), thereby stabilising the molecule and preventing the action of Factor H. This results in the continual activation of the alternative complement pathway [1]. The test should be requested in any patient with an unexplained, isolated low C3. The test is only indicated if the C3 concentration is below normal and the C4 is within the reference range [1]. The presence of C3 nephritic factor has been observed in a variety of disorders; including membranoproliferative glomerulonephritis, post-streptococcus glomerulonephritis, partial lipodystrophy, SLE, urticarial vasculitis, with hypocomplementemia being a common feature. Approximately two-thirds of patients with partial lipodystropy have a low C3 and circulating C3 nephritic factor, and have an increased tendency to develop membranoproliferative glomerulonephritis [2].

References: PRU Handbook of Clinical Immunochemistry. 9th Edition. 2007. [Ref 1] Tsokos GC. Nephritic factor autoantibodies. Autoantibodies. 2007. 2nd Ed. Elsevier. 561-566 Appel GB, et al. Membranoproliferative glomerulonephritis type II (dense deposit disease): an update. J Am Soc Nephrol. 2005. 16(5):1392-1403. Misra, et al. Clinical features and metabolic and autoimmune derangements in acquired partial lipodystrophy: report of 35 cases and review of the literature. Med (Baltimore). 2004. 83:18-34. [Ref 2]

See Also: C3

Telephone Gateshead Lab: 0191.4456499 Option 4, Option 1