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Can serum tryptase level differentiate between anaphylaxis and anaphylactoid reaction?

Asked by Anonymous 

The term "anaphylaxis" has traditionally been reserved for IgE-dependent events, and the term "anaphylactoid reaction" has been used to describe IgE-independent events, although the two reactions are often clinically indistinguishable.

The current approach for using tryptase to confirm anaphylaxis is to apply a formula termed the “20+2 rule” where the tryptase level during a symptomatic episode must equal or exceed a 20% increase over a BST measurement plus 2 ng/ml. 

Reference: https://www.aaaai.org/tools-for-the-public/latest-research-summaries/the-journal-of-allergy-and-clinical-immunology/2021/tryptase

In cases of clinical anaphylaxis with a normal level of beta-tryptase, pathogenic mechanisms (basophil activation or complement-mediated anaphylactoid reactions) other than mast cell degranulation should be considered.

Reference: Payne V, Kam PC. Mast cell tryptase: a review of its physiology and clinical significance. Anaesthesia. 2004 Jul;59(7):695-703. doi: 10.1111/j.1365-2044.2004.03757.x. PMID: 15200544.

Plasma tryptase levels were not significantly elevated in confirmed anaphylactoid reactions, so they can be used to distinguish chemical from immunologic reactions.

Reference: Renz CL, Laroche D, Thurn JD, Finn HA, Lynch JP, Thisted R, Moss J. Tryptase levels are not increased during vancomycin-induced anaphylactoid reactions. Anesthesiology. 1998 Sep;89(3):620-5. doi: 10.1097/00000542-199809000-00010. PMID: 9743397.
  1. Anaphylactoid reactions do not require sensitization and can occur at 1st exposure. However, both of these are due to mast cell degranulation and tryptase is released along with histamine. So, the general logic is that, the tryptase must be elevated in both the conditions. However, as mentioned in one of the article as above, it might not be elevated in complement mediated anaphylactoid reactions.