Clinical Assessment of a Point-of-Care Serum Amyloid A Assay in Foals with Bronchopneumonia

Despite the paucity of data available, stall-side serum amyloid (SAA) assays are commonly used to make diagnostic and treatment decisions in foals with bronchopneumonia.

Measurement of SAA concentrations can accurately differentiate pneumonic from healthy foals.

Fifty-four pneumonic foals between 3 weeks and 5 months of age were compared to 44 healthy controls. In addition, 47 foals on a farm endemic for R. equi infections were studied.

Serum samples were collected from pneumonic foals at hospital admission. Foals were categorized as having pneumonia caused by R. equi or by other microorganisms based on culture of a tracheobronchial aspirate. In addition, serum samples were obtained at 2-week intervals from foals born at a farm endemic for R. equi. SAA concentrations were measured by a point-of-care assay. Diagnostic performance of SAA was assessed by use of receiver operating characteristic curves.

Concentrations of SAA in foals with bronchopneumonia were significantly (P < 0.001) higher than those of healthy foals, but 15 of 54 pneumonic foals (28%) had SAA concentrations <5 μg/mL. There was no correlation between SAA concentrations and radiographic score in foals with R. equi pneumonia. The ability of SAA to predict development of R. equi pneumonia at the endemic farm was limited with a sensitivity of 64% and a specificity of 77%.

Overall, SAA concentrations are significantly higher in pneumonic than in healthy foals. However, performance of SAA in detecting pneumonic foals is limited by the high proportion of false-positive and false-negative results.