Alternative Pathway Haemolytic Complement (AP50)

Immunology

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Description

AP50 is a functional measure of alternative complement pathway activity. The Alternative complement pathway is an enzyme cascade dependent on stabilisation of C3b on microbial membranes. Low AP50 values may be caused by complement consumption or deficiency of complement components or regulatory factors. Deficiencies of membrane attack complex components would lead to absent AP50 and CH50 results, whereas Factor B, D and properdin deficiencies would show normal CH50 values in the absence of AP50 activity [2,3]. Suspected complement deficiency should be investigated in anyone with an unusual strain of neisserial meningitis or recurrent infections with encapsulated bacteria [1].

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Indications

Suspected Complement deficiency / recurrent meningitis. Rare alternative pathway complement deficiencies with normal CH50 (e.g. Properdin).

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Sample Type

2mL Serum (Gel 5mL Yellow tube). Serum should be separated within 2 hrs of venesection. Requests from outside Sheffield: Serum can be sent overnight at ambient temperature on the day the sample is taken or stored at 4C over a weekend and then sent overnight at ambient temperature. Samples that have been stored frozen prior to posting must remain frozen during transit. Samples can be sent via Royal Mail or Courier but must be received the morning after posting

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Reference Range

30 - 113%.

Reference range manufacturer derived and verified in house.

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Turnaround Time

Within 10 days

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Testing Frequency

Weekly

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External Notes

Serum samples taken on a Friday are stable at 4C for storage over a weekend. The sample should be posted on the Monday to reach Sheffield on Tuesday morning.

If serum samples have been frozen prior to sending to Sheffield they must remain frozen during transit. If a sample thaws out during transit it will still be assayed but some activity may have been lost. If the sample gives a value below the normal range a comment asking for a fresh sample will be added to the report.

EDTA plasma samples should not be used as the chelation of calcium ions render some of the Complement components to be inactive

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References

Tedesco F. Inherited complement deficiencies and bacterial infections. 2008. Vaccine. Suppl 8: I3-I8. [Ref 1]
PRU handbook of Clinical Immunochemistry. 9th Ed. 2007. [Ref 2]
Zipfel PF, et al. Complement and diseases: Defective alternative pathway control results in kidney and eye diseases. 2006. Mol Imm. 43:97-106.
Wen L, Atkinson JP, Giclas PC. Clinical and laboratory evaluation of complement deficiency. J Allergy Clin Immunol. 2004. 113(4):585-593. [Ref 3]

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See Also

CH50
C5-C9

Please note: the above information is subject to change and we endeavour to keep this website up to date wherever necessary.