A cytokine panel and procalcitonin in COVID-19, a comparison between intensive care and non-intensive care patients

Procalcitonin (PCT) is an acute-phase reactant with concentrations ≥0.5 μg/L indicative of possible bacterial infection in patients with SARS-CoV-2 infection (COVID-19). Some with severe COVID-19 develop cytokine storm secondary to virally driven hyper-inflammation. However, increased pro-inflammatory cytokines are also seen in bacterial sepsis. This study aimed to assess the clinical utility of a cytokine panel in the assessment of COVID-19 with bacterial superinfections along with PCT and C-reactive protein (CRP).

The retrospective analysis included serum cytokines (interleukins; IL-1β, IL-6, IL-8 and tumour necrosis factor (TNFα)) measured using Ella™ (Bio-Techne, Oxford, UK) and PCT measured by Roche Cobas (Burgess Hill, UK) in patients admitted with COVID-19 between March 2020 and January 2021. Patients enrolled into COVID-19 clinical trials, treated with Remdesivir/IL-6 inhibitors were excluded. The cytokine data was compared between intensive care unit (ICU) patients, age matched non-ICU patients and healthy volunteers as well as ICU patients with high and normal PCT (≥0.5 vs. <0.5 μg/L).

Cytokine concentrations and CRP were higher in COVID-19 patients (76; ICU & non-ICU) vs. healthy controls (n = 24), all p<0.0001. IL-6, IL-8, TNFα and were higher in ICU patients (n = 46) vs. non-ICU patients (n = 30) despite similar CRP. Among 46 ICU patients, the high PCT group (n = 26) had higher TNFα (p<0.01) and longer ICU stay (mean 47 vs. 25 days, p<0.05). There was no difference in CRP and blood/respiratory culture results between the groups.

Pro-inflammatory cytokines and PCT were higher in COVID-19 patients requiring ICU admission vs. non-ICU admissions despite no difference in CRP. Furthermore, TNFα was higher in those with high PCT and requiring longer ICU admission despite no difference in CRP or rate of bacterial superinfection.