18th March 2024

Investigations for DIA

As in all allergic diseases, a careful and chronological history is essential. The temporal relationship between drug administration and symptoms is important, as in true anaphylaxis, the reaction is rapid (within minutes). In the acute setting, serial serum mast cell tryptase measurements may be useful to confirm mast cell activation and anaphylaxis. Levels may not rise until 30 minutes after the onset of symptoms and peak at 1-2 hours. Tryptase has a short half-life and timing of measurements must be carefully documented as levels may have normalised within 6 hours. It is important to remember that a normal tryptase level does not exclude anaphylaxis.

Despite thorough history-taking, identification of the causative medication can be difficult and, particularly in the case of polypharmacy, further investigations may be helpful. Skin prick testing (SPT) may be less informative than in the investigation of food and venom-induced anaphylaxis and is poorly validated except in specific examples. Intradermal testing can be used in the context of negative SPT using increasing concentrations of diluted medication and observing for symptoms. Similarly, specific IgE testing in the context of medications can be of limited use; therefore, often, direct oral challenge is required. While sometimes it is feasible to avoid certain medications for some patients, there are examples when it is important to definitively prove or disprove hypersensitivity. Examples of this may include concerns of antibiotic-induced anaphylaxis in patients requiring long-term or prophylactic antibiotics such as bronchiectasis or in patients requiring procedures under general anaesthetic.