Complement Alternative Pathway (AH50) Functional Assay Services

Clinical Significance

Complement protein is a component of the innate immune system. There are 3 pathways for complement activation: (1) the classical pathway, (2) the alternative pathway (or properdin) pathway, and (3) the lectin (or mannose-binding lectin, MBL) pathway.

The total complement (CH50) test (COM/complement, total, serum) is the best screening method for most complement abnormalities. It evaluates the classical complement pathway, including the early components that activate the pathway in response to immune complexes, and the late components that participate in membrane attack complexes. If there are specific inherited or acquired C1-C9 complement component defects, or due to immune (or autoimmune) complex depletion of complement, the CH50 measurement will be abnormal.

The AH50 assay is a screening test for complement abnormalities in alternative pathways. The alternative pathway shares C3 and C5-C9 components, but has unique early complement components, namely factors D, B and P, and regulatory factors H and I. This pathway can be activated by C3 hydrolysis or microbial polysaccharides, and may not require the formation of immune complexes. Patients with diffuse infection of purulent bacteria under normal CH50 conditions may have lower AH50 due to genetic or offspring pathway defects. Patients with a deficiency of alternative pathway factors (D, B, P, H, and I) or a lack of late complement components (C3, C5-C9) are unusually susceptible to recurrent Neisser’s meningitis. The use of CH50 and AH50 analysis can identify abnormalities in specific pathways.

Applications

Unregulated alternative pathways can also cause disease. Most of these diseases are accompanied by renal impairment, such as atypical hemolytic uremic syndrome (a-HUS), dense deposits disease (DDD) and C3 glomerulonephritis (C3GN).

The AH50 assay Investigates suspected alternative pathway complement deficiency, atypical hemolytic uremic syndrome, C3 glomerulonephritis, compact disease.

Test Details

Methodology: Enzyme Linked Immunosorbent Assay (ELISA)
Assay Category: This test uses a reagent or kit labeled by the manufacturer as research use only.
Reference Range(s): ≥46% normal
Minimum Volume: 0.2 mL
Transport Temperature: Frozen
Specimen Stability
Room temperature: Frozen: 14 days

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