This paragraph is from an article about food induced anaphylaxis :

Currently, total tryptase level is the most commonly measured marker to establish a diagnosis of anaphylaxis. Tryptase levels increase immediately, peak at 1–2 h and return to baseline 24 h after complete resolution of symptoms. Levels are ideally obtained within 3 h of onset of symptoms and serial measurements may help establish a diagnosis of anaphylaxis.[62] Lack of tryptase elevation is commonly seen in food-induced anaphylaxis,[60,63] which may be due to slow onset of reactions or because mucosal mast cells and basophils, the major players in food-induced anaphylaxis, contain less to no tryptase as compared with skin mast cells.[25] Another laboratory marker of anaphylaxis is serum histamine which peaks at 10 min and disappears in 60 min and is therefore not a practical marker. Urinary histamine metabolites remain elevated for up to 24 h and may be helpful in establishing the diagnosis. Among other mast cell mediators, chymase, and mast cell carboxypeptidase A3 may be other potential markers of anaphylaxis.[64]

(http://www.medscape.com/viewarticle/741823_8)

I know that this is written in the context of an IgE reaction, which is not underlying the anaphylaxis many here are experiencing, but what leapt out at me was the comment about mucosal mast cells not containing the tryptase levels of skin mast cells.   Might explain why some people trying to get a diagnosis are battling with the lack of tryptase levels to prove anaphylaxis or mast cell involvement.