Elevated procalcitonin concentrations in severe Covid-19 may not reflect bacterial co-infection

Background The variability of Covid-19 severity between patients has driven efforts to identify prognosticating laboratory markers that could aid clinical decision-making. Procalcitonin is classically used as a diagnostic marker in bacterial infections, but its role in predicting Covid-19 disease severity is emerging. We aimed to identify the association between procalcitonin and Covid-19 disease severity in a critical care setting and whether bacterial co-infection is implicated. Methods We retrospectively reviewed Covid-19 patients with procalcitonin concentrations measured in a critical care setting at our institution between February and September 2020. Laboratory markers including peak procalcitonin values and a range of bacterial culture results were analysed. Outcomes were the requirement and duration of invasive mechanical ventilation as well as inpatient mortality. Results In total, 60 patients were included; 68% required invasive mechanical ventilation and 45% died as inpatient. Univariate analysis identified higher peak procalcitonin concentrations significantly associated with both the requirement for invasive mechanical ventilation (OR: 3.2, 95% CI 1.3-9.0, P = 0.02) and inpatient mortality (OR: 2.6, 95% CI 1.1-6.6, P = 0.03). Higher peak procalcitonin concentrations was an independent predictor of mortality on multivariate analysis (OR 3.7, 95% CI 1.1-12.4, P = 0.03). There was a significant positive correlation between increased peak procalcitonin concentrations and duration on invasive mechanical ventilation. No significant difference was found between peak procalcitonin concentrations of patients with positive and negative bacterial cultures. Conclusions Elevated procalcitonin concentrations in Covid-19 patients are associated with respiratory failure requiring prolonged invasive mechanical ventilation and inpatient mortality. This association may be independent of bacterial co-infection.