The invention provides a use of platelet activating factor acetylhydrolase (PAF-AH) activity as a biomarker for severe or fatal anaphylaxis in a subject. The level of PAF-AH activity inversely correlates with the susceptibility to severe or fatal anaphylaxis. The use comprises assaying PAF-AH activity in a sample from the subject and comparing the measured activity to a reference value, wherein a lower level of measured PAF-AH activity relative to said reference level of PAF-AH activity indicates a presence of or susceptibility to severe or fatal anaphylaxis in the subject. A method for treating or preventing severe or fatal anaphylaxis in a subject is also provided. The method comprises increasing serum platelet activating factor acetylhydrolase (PAF-AH) concentration in the subject by administering to the subject, PAF-AH and/or a PAF receptor antagonist. A composition for treating severe or fatal anaphylaxis is also provided.
