Serum C‐Reactive Protein as a Diagnostic Biomarker in Dogs with Bacterial Respiratory Diseases

BACKGROUND: C‐reactive protein (CRP) is a major acute‐phase protein in dogs. Serum concentrations are low in healthy animals, but increase rapidly after inflammatory stimuli. OBJECTIVE: The aim of the study was to investigate CRP concentrations in various respiratory diseases of dogs and to determine if CRP can be used as a biomarker in the diagnosis of bacterial respiratory diseases. ANIMALS: A total of 106 privately owned dogs with respiratory diseases (17 with bacterial tracheobronchitis [BTB], 20 with chronic bronchitis [CB], 20 with eosinophilic bronchopneumopathy [EBP], 12 with canine idiopathic pulmonary fibrosis [CIPF], 15 with cardiogenic pulmonary edema [CPE], and 22 with bacterial pneumonia [BP]) and 72 healthy controls. METHODS: The study was conducted as a prospective cross‐sectional observational study. CRP was measured in serum samples. Diagnosis was confirmed by clinical and laboratory findings, diagnostic imaging, and selected diagnostic methods such as cytological and microbiological analysis of respiratory samples, echocardiography, and histopathology. RESULTS: Dogs with BP had significantly higher CRP concentrations (median, 121 mg/L; interquartile range, 68–178 mg/L) than dogs with BTB (23, 15–38, P = .0003), CB (13, 8–14, P