Acquired causes of low C3, C4, and CH50

Disease	Number of cases	Percent of total
Systemic lupus erythematosus	72	65
Parvovirus infection	9	8
Rheumatoid arthritis-associated vasculitis	8	7
Liver failure*	6	5
Autoimmune hemolytic anemia	6	5
IgG₄-positive multiorgan lymphoproliferative syndrome	6	5
Cryoglobulinemia	3	3
Membranoproliferative glomerulonephritis	3	3
Acute glomerulonephritis	3	3
Autoimmune pancreatitis	2	2

The table depicts various causes of acquired hypocomplementemia and the relative frequency of each disorder in a study of 121 Japanese patients. Patients had to have a low C4, C3, and total hemolytic complement (THC) to be included. A cause was determined in 111. By requiring both a low C4 and C3, the authors selected for patients with classical pathway activation. The antiphospholipid syndrome is also commonly associated with low C4 and C3 (in the presence or absence of systemic lupus erythematosus). These results have also been seen in other populations.

IgG: immunoglobulin G.

* Mechanism of hypocomplementemia in this situation is reduced hepatic synthesis while the others represent accelerated consumption.

Data from: Saeki T, Ito T, Yamazaki H, et al. Hypocomplementemia of unknown etiology: an opportunity to find cases of IgG4-positive multi-organ lymphoproliferative syndrome. Rheumatol Int 2009; 30:99.

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Acquired causes of low C3, C4, and CH50