Community acquired pneumonia (CAP) is a common serious respiratory infection in children, which refers to pneumonia that develops within 48 h of hospital admission in healthy children who acquire an infection outside the hospital or are infected with a definite incubating agent, such as bacteria, mycoplasma pneumoniae, and viruses [9]. Globally, nearly 3.5 million children die each year from respiratory infections, with CAP accounting for the majority of these deaths [22]. Children are more susceptible to lung infections because of their immature immune function and lower resistance than adults.

Bacterial pneumonia is the most common pulmonary infections [10], which has insignificant early symptoms but progresses rapidly and is prone to misdiagnosis leading to serious consequences such as sepsis due to the low sensitivity and long-time frame of pathogenic detection, ranking as the 1st cause of death in children under 5 years of age [7]. Therefore, it is important to find biomarkers with high sensitivity and specificity for early diagnosis of bacterial pneumonia.

Serum biomarkers are potential valuable diagnostic tools. C-reactive protein (CRP) and procalcitonin (PCT) have been widely tested for the diagnosis of pneumonia [17, 18]. In recent studies, serum Amyloid A (SAA) was predictive of stroke-associated infections, especially pneumonia [23]. However, there is a lack of a single biomarker for the diagnosis of early bacterial pneumonia, and a combination of multiple biomarkers may solve this challenge. This work attempted to investigate the diagnostic value of the combined test of CRP, PCT, and SAA to differentiate bacterial pneumonia from non-bacterial pneumonia in children with CAP.