(483) Procalcitonin as an Indicator of Gram-Negative or Gram-Positive Pneumonia

Introduction: Elevated procalcitonin (PCT) is an established marker of bacterial infection in sepsis and pneumonia. Recent studies have shown that higher PCT levels may be associated with Gram-negative infections versus Gram-positive infections in bacteremia and sepsis, but this has not been evaluated in pneumonia. The objective of this study was to determine if there is an association between PCT level and isolation of Gram-negative or Gram-positive bacteria in pneumonia.

Methods: This was a retrospective cohort study that included patients > 18 years old with pneumonia confirmed by radiology, at least 2 of 4 cardinal symptoms, an elevated PCT level (>0.25 ng/mL), and positive respiratory culture from August 1, 2017 to August 1, 2022. Patients were excluded if they had active cancer, received renal replacement therapy, surgery or diagnosis of COVID-19 within 3 days of PCT level, or had cultures with polymicrobial growth or growth of Staphylococcus epidermidis or Corynebacterium species. Baseline demographic data, PCT level, and microbiology were collected on each patient. The primary outcome was median PCT level in patients with Gram-negative or Gram-positive bacterial pneumonia. The secondary outcome was PCT level associated with specific bacterial organisms.

Results: 75 patients met inclusion criteria and were included for analysis; 40 Gram-positive isolates and 35 Gram-negative isolates. Baseline demographics were similar between both groups. All isolates in the Gram-positive group were Staphylococcus aureus. The majority of isolates in the Gram-negative group were Pseudomonas aeruginosa and Klebsiella pneumoniae. The median PCT levels for Gram-positive isolates and Gram-negative isolates were 0.61 ng/mL and 1.46 ng/mL (p=0.090), respectively. Median PCT levels between different bacterial organisms were 0.61 ng/mL for Staphylococcus aureus, 1.95 ng/mL for Pseudomonas aeruginosa, and 0.91 ng/mL for Klebsiella pneumoniae (p=0.117).

Conclusions: There was not a statistically significant difference between median PCT levels in Gram-negative and Gram-positive isolates; however, the median PCT level was numerically higher for Gram-negative isolates. More data in a larger, prospective, population is needed to determine if this association exists in pneumonia.