In this retrospective single center cohort study we included patients who visited the ED of Erasmus University Medical Center, in Rotterdam, the Netherlands, with a confirmed COVID-19 infection between 1 March 2020 and 31 December 2020. Erasmus University Medical Center is an academic hospital with 40.000 ED visits annually. The institutional review board waivered informed consent for the retrospective use of clinical data of COVID-19 patients.
Inclusion and exclusion criteria
Patients were included if they tested positive on COVID-19 positive by PCR test at the day of the ED visit, the reason for ED visit was related to the COVID-19 infection and PCT levels were measured in the ED. Patients were excluded if the PCT levels were measured but invalid (e.g. hemolytic blood samples), if the COVID-19 infection was a secondary finding and not the primary reason for ED visit or when no follow-up data were available due to transfer to another hospital.
Data collection
Patient data including demographics, comorbidities, vital signs and laboratory tests were collected from the electronic patient records. Vital signs including heart rate, arterial oxygen saturation, respiratory rate, temperature and blood pressure were recorded from the time of ED visit. Laboratory testing during the ED visit included hemoglobin, red cell distribution width (RDW), leucocyte count, thrombocytes, total bilirubin, alanine aminotransferase (ALAT), aspartate aminotransferase (ALAT), lactate, D-dimer, C-reactive protein (CRP) and PCT. Patients were followed up for 30 days after hospital discharge. Patient disposition from the ED was categorized into discharge home from the ED, admission to general ward and admission to the ICU. Mortality data was categorized into in-hospital mortality and mortality at home within 30 days after hospital discharge. To correct for potential bacterial coinfections at ED visit, culture within 48 hour of ED visit were reviewed. If cultures or pneumococcal or legionella antigen tests were positive, patients were classified as bacterial coinfection.
Primary outcome
The primary outcome was a severe COVID-19 infection, defined as patients that were admitted to the ICU and patients that died during 30 days follow-up.
Secondary outcomes
The secondary outcomes of this study were hospital admission, ICU admission and mortality. We calculated odds ratios (ORs) for the primary and secondary outcomes for commonly used cut-off values of PCT of 0.25 ng/mL, 0.5 ng/mL and 1.0 ng/mL.
Procalcitonin measurement
PCT analysis was available as a standard laboratory test in patients who visited the ED with a suspected COVID-19 infection. Blood was collected in a lithium heparin tube and analyzed directly upon arrival in the clinical chemistry laboratory. PCT was measured using E801 Elecsys BRAHMS PCT reagent on a COBAS 8000 (Roche Diagnostics, Switzerland). The PCT values were available to the treating physician during the ED visit.
Statistical analysis
Normally distributed variables were reported as mean with standard deviation (SD), non-normally distributed variables as median with interquartile range (IQR). Multiple imputation was used for handling missing data.
Differences in dichotomous variables between the severe and non-severe COVID-19 infection patients were analyzed with chi-square tests. Differences in continuous variables were analyzed using an independent sample T-test for normally distributed data and a Mann-Whitney-U test for non-normally distributed data.
For the primary outcome, we calculated unadjusted odds ratios of the variables that were significantly different between groups using univariate logistic regression analysis. We calculated adjusted ORs of PCT correcting for only bacterial coinfection and for gender, age bacterial coinfection and comorbidities. We constructed receiver operating characteristic (ROC) graphs and calculated the corresponding area under the curve (AUC)of continuous variables to report the predictive value on severe COVID-19 infection.
We reported PCT as a continuous variable for the primary outcome.
For the secondary outcomes, we used predefined cutoff values of 0.25 ng/mL, 0.5 ng/mL, 1.0 ng/mL of PCT and calculated the unadjusted ORs, the sensitivity, specificity, negative predictive value and positive predictive value on the primary and secondary outcomes of the study.
Statistical analyses were performed using ‘R’ version 3.6.2. We used the MICE package for multiple imputation of missing data.