Friday, March 20, 2015

C4




C4 is a component of the classic complement pathway. Depressed levels usually indicate classic pathway activation. 


Normal Range: 15-45 mg/dL


increased in: Various malignancies: not clinically useful. 
 

Decreased by: Decreased synthesis, increased catabolism (SLE, rheumatoid arthritis, proliferative glomerulonephritis, hereditary angioedema), and increased loss (burns, protein-losing enteropathies). Congenital deficiency. 
 
Additional: Low C4 accompanies acute attacks of hereditary angioedema, and C4 is used as a first-line test for the disease. C1 esterase inhibitor levels are not indicated for the evaluation of hereditary angioedema unless C4 is low. Congenital C4 deficiency occurs with an SLE-like syndrome. Test as usually performed is an immunoassay and not a functional assay.

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