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Procalcitonin levels unable to distinguish between viral and bacterial community-acquired pneumonia

13th September 2021

The use of procalcitonin levels in an emergency department is unable to distinguish between viral and bacterial community-acquired pneumonia.

Symptoms of community-acquired pneumonia (CAP) include shortness of breath, coughing, fever and chest pain some of which such as fever and coughing, overlap with COVID-19. Determining whether the causative agent in CAP is bacterial or viral can be difficult and measurement of procalcitonin levels can serve as an important biomarker for the presence of a bacterial cause. Given that higher procalcitonin levels are more likely to indicate a bacterial rather than viral cause for CAP, a team from the Emergency Department, University Libre Bruxelles, Belgium, wondered if the measurement of procalcitonin levels could help distinguish between viral and bacterial CAP in patients infected with COVID-19 and retrospectively analysed data for a cohort of patients admitted to their emergency department.

All patients who were admitted with a suspicion of CAP had their procalcitonin levels measured. Subsequently, enrolled patients were those with clinical signs of a lower respiratory tract infection and with at least one symptom of acute respiratory illness, e.g., cough, dyspnoea, sputum production, tachypnoea and pleuritic chest pain. Other inclusion criteria were those with signs of an acute infection, e.g., temperature > 38oC, chills, altered mental status and a leucocyte count > 10,000/microL and oxygen saturation < 94%. Only patients who underwent both bacteriological, viral and radiological imaging (CT) within 48 hours of admission were subsequently included. Patients were classified as having bacterial CAP based on both microbiological analysis and the findings from the CT scan. Alternatively, patients were classed as having viral CAP in the absence of positive bacteriological findings and where the CT scan indicated a high suspicion of viral pneumonia.

During the period of the study, 3593 patients visited the emergency department with symptoms potentially related to COVID-19 and 151 were subsequently included in the analysis after applying the inclusion criteria, of whom, 138 had a microbiologically confirmed bacterial pathogen. Among those with diagnosed viral CAP, 112 had COVID-19-related pneumonia. The discriminatory accuracy of procalcitonin levels for bacterial and viral CAP were calculated from receiver operating characteristic (ROC) curves. The median procalcitonin levels were higher in bacterial CAP (0.53ng/ml vs 0.16ng/ml, bacterial vs viral, p = 0.005). Using the ROC curves to discriminate between viral and bacterial CAP generated an area under the curve (AUC) of 0.68 (95% CI 0.53 – 0.83). Based on a threshold procalcitonin level of > 0.5ng/ml, to identify bacterial CAP, gave a sensitivity of 52.2% and a specificity of 82%.

Commenting on their findings, the authors noted that there were no procalcitonin levels which were able to differentiate between bacterial CAP and COVID-19 associated pneumonia. Based on their findings, the authors calculated that the administration of antibiotics to those with procalcitonin levels > 0.5ng/ml would have resulted in the inappropriate treatment of 65.7% of patients with radiological signs of CAP.

They concluded that procalcitonin measurements upon admission in those with suspected CAP cannot accurately differentiate between bacterial or viral CAP.

Malinverni S et al. Is procalcitonin a reliable marker of bacterial community-acquired pneumonia in adults admitted to the emergency department during SARS-CoV-2 pandemic? Eur J Emerg Med 2021

Procalcitonin levels predictive of severe disease in COVID-19

23rd July 2021

Measurement of procalcitonin levels was found to be most discriminatory for severe disease course among patients hospitalised with COVID-19.

Knowledge about COVID-19 has advanced at rapid pace over the last 15 months and with a large number of patients being admitted to hospital, it is of upmost importance to be able to assess which patients are at the highest risk of disease progression. Based on earlier observational studies, it has become clear that older patients and those with co-morbidities are more likely to develop severe disease and several biomarkers including C-reactive protein and procalcitonin, have been shown to be associated with severe disease. A further potential complication of COVID-19 is bacterial co-infection though in an analysis of 24 studies including 3338 patients, the presence of bacterial co-infection in COVID-19 was found to be very low at 6.9%. Nevertheless, whether the use of biomarkers such as procalcitonin could be used to identify bacterial co-infection among patients with COVID-19 has been suggested as a potentially valid strategy, but there is a lack of evidence to support this approach.

This absence of evidence prompted a team from the Department of Internal Medicine, Haga Teaching Hospital, Den Haag, The Netherlands, to retrospectively evaluate the association between multiple biomarkers, including procalcitonin and the clinical and microbiological outcomes in patients hospitalised with COVID-19. The team used data from the PredictED study, a single centre, prospective observational study, designed to evaluate procalcitonin as a marker for bacteraemia in patients who present to the emergency department. While the original study was designed to examine all patients admitted to the emergency department, the authors turned to a subset of patients with PCR-confirmed COVID-19. A number of tests were undertaken, including blood cultures, C-reactive protein and procalcitonin although the results of this latter test were not immediately available to the treating clinician. The primary outcome of the study was the incidence of bacterial co-infection at the initial emergency department presentation and its association with procalcitonin.

The subset of COVID-19 patients testing positive for the virus was 142 with a mean age of 61 years (66% male). More than half of these patients had co-morbidities including diabetes (25%) and cardiovascular disease (24%) and from the complete cohort, 41 developed severe COVID-19, all of whom were hospitalised and 24 (17%) subsequently died within 30 days. Procalcitonin levels were significantly associated with the development of severe disease (odds ratio, OR = 1.8, 95% CL 1.3 – 2.2), as were higher levels of the biomarker. In addition, C reactive protein levels were also significantly associated with more severe disease (OR = 1.8, 95% CI 1.3–2.6). Using the area under the receiver operating curve for procalcitonin, the predictive value was 0.76.

Commenting on their results, the authors noted that procalcitonin demonstrated the highest discriminatory power between severe and non-severe COVID-19. Although only a small number of COVID-19 patients (1.4%) had a bacterial co-infection, the authors concluded that measurement of procalcitonin levels appeared to be a promising approach to help clinicians recognise patients a higher risk of more severe COVID-19 infection.

Kaal A et al. Diagnostic yield of bacteriological tests and predictors of severe outcome in adult patients with COVID-19 presenting to the emergency department. Emerg Med J 2021