ObjectiveTo determine the quality and diagnostic accuracy of in-hospital adult clinical emergency calls.DesignProspective observational study.SettingThree National Health Service acute hospitals in England.ParticipantsAdult patients sustaining an in-hospital cardiac arrest (CA) or medical emergency (ME) which required activation of the hospital resuscitation team between 1 December 2009 and 30 April 2010.Main outcome measuresEmergency call duration, emergency team dispatch time, diagnostic accuracy of emergency call (sensitivity/specificity), thematic analysis of emergency call, patient outcomes (return of spontaneous circulation and survival to hospital discharge).ResultsThere were 426 adult resuscitation team activations. There was variability in emergency call duration ranging from 6 to 92 s (median 15 s; IQR 12-19). The sensitivity and specificity of calls for a CA was 91% (86.4-94.6%) and 62% (55.5-68.7%), respectively. Sensitivity did not change with call duration but specificity increased from 38% (25.8-51.0%) for the shortest calls to 82% (69.5-89.6%) for longer calls; p=0.03. The return of spontaneous circulation rate was 38% for calls when the patient was confirmed as in CA upon arrival of the resuscitation team. Survival to hospital discharge rates was higher in patients with shorter call durations (26%) than calls with longer call duration (12%); p=0.028. Five themes emerged identifying reasons for the increased call delay.ConclusionThere is variability in duration and diagnostic accuracy of in-hospital emergency calls. This is associated with delayed activation of the emergency response. The attempt to differentiate between ME and CA is a source of confusion. A single clinical emergency response for CA and ME calls may provide a more focused and timely emergency response.