Laboratory Test Reference Guide

Two samples should be collected; one sampled between 15 mins and 3 hours post anaphylactic reaction, and one 24 hours post anaphylactic reaction. Specimens taken outside this time frame may give misleadingly low results.

300uL Serum
EDTA or Heparin plasma also acceptable.

Chilled

Requests must be supported by a SMO.

Trytpase measurement is indicated when a mast cell disorder is suspected. It can also be useful for confirmation of anaphylaxis when the diagnosis is not clear, for example in collapse immediately following an IV injection or sting, without development of mucocutaneous features of histamine release, or bronchospasm. It is particularly useful in anaesthesia when several things may account for collapse. 

Tryptase is not elevated in all anaphylaxis; it often does not increase in food allergy so if the diagnosis is clear there is no added benefit of doing the test. In patients presenting with recurrent anaphylactic like-symptoms the tryptase may be useful to confirm that anaphylaxis is occurring.

Tryptase half-life is 2 hours, so there is no point doing the test the next day. If the tryptase is raised then a repeat level should be taken > 24 hours later to ensure it returns to normal. If it remains elevated, then a mast cell disorder is likely.  A single normal tryptase is often unhelpful.  It is possible to have significant anaphylaxis (with a doubling of tryptase from baseline) but where the elevation from baseline remains within the normal range.

For cases of suspected anaphylaxis in patients undergoing anaesthesia there are ANZAAG guidelines on testing which recommends testing 1, 4 and 24 hours post reaction. House surgeons on the ward can request these under the direction of the treating anaesthetist.