Objectives: To study predictors for biphasic anaphylaxis in Thai patients at the Emergency Department (ED).

Methods: All consecutive patients diagnosed as anaphylaxis at the ED, Ramathibodi Hospital, Mahidol University, Bangkok were enrolled. The study was prospectively conducted from January to December 2011. Patients were divided into two groups; uniphasic and biphasic anaphylaxis. Multivariate logistic regression was used to identify factors associated with biphasic anaphylaxis.

Results: During the study period, there were 63 patients diagnosed with anaphylaxis at the ED. Of those, 16 patients were excluded due to incomplete clinical data in regards of diagnosis or treatment of anaphylaxis, concomitant medications or pre hospital treatment. In total, there were 47 patients remaining in the study, including 10 patients with biphasic anaphylaxis (21.28%). The clinical characteristics of the uniphasic and biphasic anaphylaxis groups were comparable. In multivariate logistic regression analyses, only respiratory rate and abdominal pain were significantly associated with biphasic anaphylaxis. The adjusted ORs (95% CI) of both factors were 0.653 (0.457, 0.932) and 15.429 (1.395, 170.690), respectively.

Conclusion: Reduced respiratory rate and the presence of abdominal pain were two significant factors associated with biphasic anaphylaxis.