NCEPOD reported in 2012 that 75% of patients had warning signs for cardiac arrest present prior to their arrest [1]. NICE recommends a vital sign-based early warning score (EWS) to identify patients at risk of deterioration or death [2]. In our trust, audit has shown that only 20 to 35% of patients trigger the clinical EWS prior to cardiac arrest. Jarvis and colleagues proposed that an EWS based on common laboratory findings can predict patient mortality [3]. The aim of this study, as part of a wider review of cardiac arrests in our hospital, was to determine whether the laboratory early warning score (LEWS) might be of use identifying patients at risk of cardiac arrest in our trust.