COVID-19, caused by SARS-CoV2, is a novel biphasic disease that may be associated with significant morbidity and mortality in the second phase of illness in select groups of infected individuals. There is significant interest in testing the utility of biomarkers in the first phase of illness for identifying individuals at higher risk of deterioration who may benefit from closer home or hospital monitoring. Calprotectin is an example of such a blood plasma biomarker that is widely hailed as a potentially independent predictor of deterioration. We have been measuring calprotectin in individuals presenting with suspected COVID-19 disease within 48 hours of presentation during the 2020-21 winter surge in a real-time manner using an assay set up in biochemistry. The results are stored on the biochemistry LIMS system and clinicians are blinded to the results given their uncertain clinical utility. Here we propose to link clinical data to these measures and test whether calprotectin levels within 48 hours of early assessment are a predictor of deterioration (as measured by a composite measure of need for non-invasive ventilation or admission onto intensive care or death) independent of current clinical or biochemical predictors.