Advanced Diagnostic Laboratories

Test Code

Alternative Complement Pathway Activity (AM50)

Description

The complement system is part of our innate immune response. It is vital to our defense against invasive microorganisms. Complement activation can occur through the classical, lectin and alternative pathway, which then converge to a common terminal pathway. Activation of the complement pathway(s) results in the generation of biologically active peptides, also known as complement split products, and referred to as anaphylatoxins (C4a, C3a, C5a) which protect us from invasive microorganisms by enhancing inflammation, facilitating the clearance of immune complexes and apoptotic cells, enhancing cellular, and antibody immune responses, and altering vascular permeability, as well as smooth muscle contractility.

Complement deficiency can lead to life-threatening infections well as long-term autoimmune conditions such as systemic lupus erythematosus (SLE) and hereditary angioedema (HAE). The AH50 hemolytic assay is a sensitive method for detection of total alternative complement activity or lack thereof. Severe or recurrent infections that produce strong activation of the classical complement pathway may lower AH50 levels below normal. Genetic or acquired complement deficiency involving the alternative complement pathway components (Factor B, Factor D, Properdin, and C3) as well as terminal complement components (C5, C6, C7, C8, and C9) may lower AH50 levels. Severe or recurrent infections that produce strong activation of the alternative complement pathway may lower AH50 levels below normal. The AH50 assay can also be utilized to monitor response to anti-complement therapies