what percentage of patients present with anaphylaxis without an obvious trigger?

The percentage of patients presenting with anaphylaxis without an obvious trigger is estimated to be around 20% to as high as 32–50% in some reports, often referred to as idiopathic anaphylaxis. In many of these cases, no clear external allergen or cause can be identified despite investigation, although some may be due to hidden or unusual triggers, or temporary increased immune reactivity. This means that roughly one-fifth to nearly half of anaphylaxis cases may initially appear without a known trigger.