Performance of the Procalcitonin Test in Diagnosing Pneumonia in Real-World Practice

Abstract

Abstract Background Procalcitonin (PCT) rises early upon bacterial infection and has a long-half life, making it useful in the diagnosis of infections and antibiotic stewardship. We sought to determine the utility of PCT in diagnosing pneumonia (PNU) in the patient population presenting to our hospital during real-world clinical practice. Methods PCT results from patients in 2015 were reviewed retrospectively. Patients were eligible for inclusion if all of following criteria were met: PCT in 2015 and a lower respiratory tract culture, respiratory virus testing, chest x-ray, and white blood cell (WBC) count within 1 day of the PCT. Patients who opted out of research and those with mycobacterial infections and culture-positive infections of body sites other than urine and lower respiratory tract were excluded from further analysis. Results A total of 400 patients remained with 413 eligible PCT results across the ED (109), ICU (134), and inpatient (167) and outpatient (3) areas with a mean (SD) age of 66.2 (18.1). PCT was higher in patients with multiple pathogens reported on their respiratory cultures, direct fluorescence antibody (DFA), or PCR-based tests (mean ± SD = 2.43 ± 0.74 ng/mL; N = 32), than those with no pathogens reported (3.25 ± 1.13 ng/mL; N = 224; P < .05). Patients were grouped for the presence or absence of clinically defined PNU, according to a modification of the Centers for Disease Control (CDC) PNU1 criteria incorporating (1) chest x-ray results, (2) altered WBC number/altered mental status/fever, and (3) respiratory/breathing signs. PCT was higher in patients with clinically defined PNU, and the high PCTs were consistent with positive chest x-rays (criterion 1), and positive criterion 2 but not criterion 3. Incorporation of an elevated PCT >0.1 ng/mL into the PNU score slightly improved the area under the ROC curve (AUC) for the algorithm’s detection of PNU against the final clinical diagnosis (0.73 without PCT vs 0.76 with PCT). Furthermore, higher PCT was associated with higher 30-day and 1-year mortality. Conclusion PCT results were largely consistent with other markers of PNU such as imaging and CDC criterion 2, which suggests that PCT can be useful in evaluating for the presence of PNU. However, the PCT may not add additional information to assist in decision making above the already commonly ordered tests.