Limited discriminatory value of C-reactive protein for viral coinfection and respiratory severity in children evaluated in the emergency department for acute respiratory tract illness.
CRP alone shows almost no ability to predict advanced respiratory support in children
Limited discriminatory value of C-reactive protein for viral coinfection and respiratory severity in children evaluated in the emergency department for acute respiratory tract illness.
C-reactive protein is often measured in children who present to an acute care facility with acute respiratory tract illness (acute respiratory tract illness), and multiplex polymerase chain reaction (polymerase chain reaction) testing on respiratory samples frequently identifies more than one pathogen per encounter in children with acute respiratory tract illness.
To assess whether age-stratified CRP differs by viral coinfection status, and whether CRP adds discriminatory value beyond clinical variables for predicting advanced respiratory support, after accounting for selection bias, probable bacterial coinfection, repeated encounters and overadjustment.
This was a retrospective encounter-level cohort study of 17,089 encounters with acute respiratory tract illness in which multiplex respiratory polymerase chain reaction (polymerase chain reaction) testing was performed in the emergency department (emergency department) between Jan 1, 2019, and Dec 31, 2025.
AUC near 0.5 means CRP performed no better than chance at predicting this outcome
Within the CRP cohort, 3,037 (61.4%) met criteria for probably bacterial coinfection.
Significant age x coinfection interactions on log-CRP were detected for RSV, common coronaviruses, adenovirus, and SARS-Cov-2 (all q , 0.05).
The coinfection-CRP signal was concentrated in emergency department-only patients ( p = 0.008) and was absent among pediatric ward ( p = 0.30) or PICU admissions ( p = 0.58).
The CRP per-10-mg/L coefficient had aOR 1.013 (1.001-1.026, p = 0.036) in the parsimonious model and aOR 1.000 (0.983-1.018, p = 0.96) when restricted to one-encounter-per-patient.
CRP testing is preferentially measured in patients who already appear sicker.
After accounting for probably bacterial infection, CRP does not reliably distinguish single from multi-virus acute respiratory tract illness except for RSV in younger children, and it does not provide clinically useful incremental discrimination beyond simple clinical variables for advanced respiratory support.