Point-of-care procalcitonin testing for lower respiratory tract infection in pulmonary outpatient care has limited value.

Lower respiratory tract infections (LRTI) are frequently the reasons for patients to visit their general practitioners or lung specialists; however, physicians tend to prescribe antibiotics less frequently than necessary. A readily available biomarker could help distinguish between viral and bacterial cause of LRTI. The primary objective of our study was to determine the diagnostic accuracy of point-of-care testing (POCT) of procalcitonin (PCT) in identifying bacterial pneumonia in outpatients with LRTI. All patients aged 18 years or older with signs and symptoms of LRTI who visited a respiratory physician were included in the study and their PCT levels were measured. In 110 patients enrolled in the study, three patients (2.7%) had PCT values above the threshold of 0.25 µg/L without proven bacterial infection, in contrast to seven patients with typical radiological signs of pneumonia without elevated POCT PCT levels. The AUC for PCT for the detection of pneumonia was 0.56 (p=0.685). POCT PCT showed limited specificity and sensitivity in distinguishing pneumonia from bronchitis or exacerbation of chronic respiratory diseases. PCT is a marker of severe bacterial infections and not suitable for milder infections in outpatient care.

C-reactive protein and procalcitonin for antimicrobial stewardship in COVID-19.

PURPOSE: Coronavirus disease 2019 (COVID-19) caused by severe acute respiratory coronavirus 2 (SARS-CoV-2) has spread around the world. Differentiation between pure viral COVID-19 pneumonia and secondary infection can be challenging. In patients with elevated C-reactive protein (CRP) on admission physicians often decide to prescribe antibiotic therapy. However, overuse of anti-infective therapy in the pandemic should be avoided to prevent increasing antimicrobial resistance. Procalcitonin (PCT) and CRP have proven useful in other lower respiratory tract infections and might help to differentiate between pure viral or secondary infection. METHODS: We performed a retrospective study of patients admitted with COVID-19 between 6th March and 30th October 2020. Patient background, clinical course, laboratory findings with focus on PCT and CRP levels and microbiology results were evaluated. Patients with and without secondary bacterial infection in relation to PCT and CRP were compared. Using receiver operating characteristic (ROC) analysis, the best discriminating cut-off value of PCT and CRP with the corresponding sensitivity and specificity was calculated. RESULTS: Out of 99 inpatients (52 ICU, 47 Non-ICU) with COVID-19, 32 (32%) presented with secondary bacterial infection during hospitalization. Patients with secondary bacterial infection had higher PCT (0.4 versus 0.1 ng/mL; p = 0.016) and CRP (131 versus 73 mg/L; p = 0.001) levels at admission and during the hospital stay (2.9 versus 0.1 ng/mL; p < 0.001 resp. 293 versus 94 mg/L; p < 0.001). The majority of patients on general ward had no secondary bacterial infection (93%). More than half of patients admitted to the ICU developed secondary bacterial infection (56%). ROC analysis of highest PCT resp. CRP and secondary infection yielded AUCs of 0.88 (p < 0.001) resp. 0.86 (p < 0.001) for the entire cohort. With a PCT cut-off value at 0.55 ng/mL, the sensitivity was 91% with a specificity of 81%; a CRP cut-off value at 172 mg/L yielded a sensitivity of 81% with a specificity of 76%. CONCLUSION: PCT and CRP measurement on admission and during the course of the disease in patients with COVID-19 may be helpful in identifying secondary bacterial infections and guiding the use of antibiotic therapy.