Mast Cell Tryptase
The essential feature of an anaphylactic response is the release of vasoactive chemicals (particularly histamine) from mast cells and circulating basophils. The presence of systemic mast cell degranulation is evidenced by an increase in serum/plasma tryptase. Serial measurements of Tryptase are made to determine if a mast cell-mediated reaction to drugs have occurred. These reactions are usually triggered by IgE antibodies. Not all drug reactions are mast cell (type 1, IgE) – mediated. Indeed, they are probably in the minority. Type 2, 3 and 4 (complement, immunoglobulin not IgE or cellular) reactions do not usually cause release of tryptase.A wide range of drugs can cause IgE mediated, the most common being anaesthetics, muscle relaxants and antibiotics. Plasma expanders and radiocontrast media can cause IgE mediated responses. Non-IgE mediated (anaphylactoid) reactions resulting in release of histamine and tryptase but mediated by other mechanisms can also occur.
Detection of mast cell-mediated reactions to the anaesthetics, other drugs or injected pharmaceuticals.
A significantly raised serum/plasma tryptase during the active reaction which subsequently subsides (24hrs) is indicative of a mast cell mediated response. Where a response has been observed it is often useful to request specific IgE to the drug suspected of causing the reaction.
Serum Separator Tube (SST) or EDTA Tube
Fluorescence enzyme linked immunoassay (Phadia Immunocap 250).
As Tryptase values usually return to normal at 24 hours post reaction, three samples (EDTA plasma or serum) are required to be taken up to 0 hours, 2 hours and more than 24 hours after a suspected anaphylatic reaction. When sending samples clearly indicate TIME OF SAMPLE and TIME OF ONSET OF REACTION. The peak response sample, i.e sample taken at 2 hour post reaction, is also be tested for C3/C4 levels. A single sample is of significantly less value but it is essential that the time of venepuncture relative to peak anaphylactic response is known.
Mast Cell Tryptase 2-14ug/ml
Assay range notes
In anaphylaxis the peak plasma concentration can be >200ug/ml. the upper range of detection using this test, but is usually much lower
5 – 7 days
Immunology, The James Cook University Hospital