Background: Currently, acute-phase proteins, such as serum amyloid A (SAA) and C-reactive protein (CRP), and the erythrocyte sedimentation rate (ESR) test are used for the diagnosis of infectious or inflammatory diseases. This study determined whether the SAA test is useful for diagnosing bacterial infections in patients visiting the emergency room (ER).
Methods: The medical records of 1,400 patients who visited the ER of Gangnam Severance Hospital from February to December 2022 were retrospectively analyzed. The groups of patients were divided based on clinical diagnoses, and the usefulness of SAA and other tests, including CRP, ESR, and complete blood count indices, in diagnosing bacterial infections was estimated.
Results: The serum levels of SAA and CRP were well correlated, showing a Spearman’s correlation coefficient of 0.844. In a multivariate analysis, SAA was identified as an independent factor associated with bacterial infections, along with other variables such as the patient’s timing of the ER visit after 24 hours of symptom onset, body temperature, platelet distribution width, neutrophil count, and ESR. However, CRP did not exhibit a significant association. As a result of the receiver operating characteristic curve analysis, the area under the curve values of SAA, CRP, and the combination of SAA+CRP+ESR+neutrophil count for the diagnosis of bacterial infection were 0.840, 0.834, and 0.848, respectively, without showing statistically significant differences with each other.
Conclusions: The SAA test would independently help diagnose bacterial infections in patients visiting the ER.

Keywords: Serum amyloid A protein, Bacterial infections, C-reactive protein, Acute-phase proteins, Emergency room