Objectives: Respiratory infections are among the most common infectious diseases, resulting in significant morbidity and mortality. C-reactive protein (CRP), serum amyloid A (SAA), procalcitonin (PCT), and interleukin-6 (IL-6) are advantageous for diagnosing respiratory tract infections. This study assessed the analytical performance and accuracy of new kits for Eu3⁺-based CRP/SAA and PCT/IL-6 lateral flow immunoassay and its diagnostic value in respiratory tract infections.

Methods: This study evaluated the detection performance of a test kit using guidelines from the Center for Medical Device Evaluation (CMDE) and the Clinical and Laboratory Standards Institute (CLSI). The test results were compared to those of the commercial kits (CRP: Mindray; SAA: Norman; PCT: Shanghai Upper; IL-6: Wantai BioPharm). A total of 156 patients with respiratory tract infections (53 with bacterial infections (Bac group); 50 with viral infections (Vir group); and 53 with co-infections (Bac + Vir group)) were enrolled, along with 50 healthy controls (HC group). Venous blood samples were collected to measure levels of SAA, PCT, CRP, and IL-6 using both the test and commercial kits. The diagnostic value of these biomarkers was assessed using receiver operating characteristic (ROC) curves.

Results: Correlation analysis demonstrated a strong concordance between the test kits and commercial kits (CRP: r = 0.9396, P < 0.0001; SAA: r = 0.8986, P < 0.0001; PCT: r = 0.9594, P < 0.0001; IL-6: r = 0.9009, P < 0.0001). The diagnostic performance of the test kits in identifying bacterial, viral, and co-infections was highly consistent with that of the commercial kit.

Conclusions: The Eu3⁺-based CRP/SAA and PCT/IL-6 lateral flow immunoassay test kits demonstrated high levels of consistency with commercial kits in terms of quantitative outcomes and diagnostic performance for respiratory tract infections.