Immunology

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Alternative name/Profile

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Investigation

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Notes

Useful for:

• Investigating patients for congenital complement deficiencies.
• Investigating patients for acquired complement deficiencies.

Clinical Information:

• Complement is a component of the innate immune system.
• Complement can be activated by three pathways; the Classical Pathway, the Alternative Pathway and the Mannose-binding Lectin (MBL) Pathway.
• The key components of the Classical Pathway are the proteins C1q, C1r, C1s, C2 and C4; of the Alternative Pathway are the proteins Factor B, Factor D, Factor H, Factor I and Properdin; and of the Mannose-binding Lectin (MBL) Pathway are the proteins C2, C4 and MBL-Associated Serine Proteases (MASPS).
• All three pathways lead to the activation of C3 and C5. 
• The common activation of C3 and C5 results in the formation of the Membrane Attack Complex (MAC) of the Terminal Pathway. This complex is capable of disrupting cell membranes to induce cell death.
• Decreased complement activation can be caused by a congenital complement deficiency or by an acquired complement deficiency.
• Deficiencies of the proteins involved in the Classical Pathway can result in a reduced ability to clear immune complexes, attract neutrophils or generate the lytic activity of the Terminal Pathway. These patients have an increased susceptability to neisserial infections and may display symptoms of autoimmune disease.
• Patients with a deficiency of a protein involved in the Alternative Pathway have an increased susceptability to recurrent neisserial meningitis.

Please Note:

• Samples for Complement CH100 must be received in the laboraory within 6 hours of collection.
• Where External Institiutions cannot guarantee immediate delivery, samples must be centrifuged, separated and frozen within 6 hours of collection. Samples can then be transported, frozen on dry ice, to St. James's Hospital for processing.
• Samples for Complement CH100 must be in the laboratory by 16:00 daily.
• A reduced or absent CH100 assay should be confirmed by repeating the assay on a fresh sample.

Related links

Reference range

Normal Complement Cascade Activation:

Classical Pathway: 32.4-125%

Alternative Pathway: 24.5-113%

Reduced Complement Cascade Activation: (Repeat sample advised for verification)

Classical Pathway: 5-32.4%

Alternative Pathway: 5-24.5%

Reference ranges determined with 13 normal patient samples, and confirmed as normal using radial immunodiffusion assays in SJH 2014.

Absent Complement Cascade Activation :

Classical and Alternative Pathway: <5%

Alternative-Absent, Total-Normal: Indicates a deficiency in the Alternative Pathway. Repeat sample advised for verification.

Alternative-Absent, Total-Absent: Indicates a deficiency in the Terminal Pathway. Repeat sample advised for verification.

Alternative-Normal, Total-Absent: Indicaties a deficiency in the Classical Pathway. Repeat sample advised for verification.

Last updated

Wed, 15 Mar 2023 12:02:55 GMT