Ambiguous triage scenarios in hospital emergency departments are often difficult to assess without decision support. Subjective assessments of such scenarios can either lead to under-triaging or over-triaging for which true conditions of patients are often not addressed within the required time. In this paper, we propose a decision support model that can guide a clinician when identifying the urgency of medical intervention when patient presents with ambiguous triage case. Our model is a heuristic approach that selects the best triage category, identifies corresponding discriminating attribute of the patient, and allows clinician to attach a level of confidence in the decision. We implemented this model as a mobile decision support system, called iTriage. Results of an initial evaluation of iTriage using fourteen paper-based adult triage scenarios showed that our model produced robust decisions for urgent scenarios. For non-urgent scenarios, the proposed model provided guidance especially when the scenarios were ambiguously stated.