Usefulness of serum amyloid A to differentiate feline inflammatory lower respiratory tract diseases from cardiac or neoplastic disease: a retrospective study of 22 cats (2021‐2024)

Objective To evaluate the usefulness of serum amyloid A concentration in differentiating inflammatory lower respiratory tract diseases from cardiac/neoplastic respiratory diseases in cats. Methods A retrospective analysis of medical records of cats presented between 2021 and 2024 to a single referral centre was performed. Cats in respiratory distress with serum amyloid A assay performed within 48 hours after admission were included and divided into two groups (inflammatory and cardiac/neoplastic). The inflammatory group included infectious or non‐infectious inflammatory lower respiratory tract diseases, and the cardiac/neoplastic group was subdivided into cardiac and neoplastic subgroups. Signalment, clinical signs and diagnostic testing results, including serum amyloid A concentration, were recorded and compared between groups ( P < .05). Results Twenty‐two cats were included. Median serum amyloid A concentration was significantly higher in the inflammatory group (57.5 μg/mL (12.2 to 70.3); n = 15) compared to the cardiac/neoplastic group (5 μg/mL (5); n = 7; P = .003). There was also a significant difference among the inflammatory, cardiac (5 μg/mL (5); n = 3) and N (5 μg/mL (5); n = 4) subgroups ( P = .01); however, pairwise comparisons were not statistically significant. The optimal serum amyloid A concentration cut‐off to differentiate between inflammatory and cardiac/neoplastic groups was 8.6 μg/mL (sensitivity of 80% (95% confidence interval: 59.5 to 91.6) and specificity of 100% (95% confidence interval: 84.6 to 100)). Clinical Significance Cardiac and neoplastic diseases were associated with low serum amyloid A concentration. Serum amyloid A concentration could be a potential diagnostic tool but larger studies are needed to validate the proposed cut‐off value. Further prospective studies are also needed to establish the usefulness of serum amyloid A concentration in distinguishing between infectious and non‐infectious inflammatory diseases.