Utility of serum amyloid A in monitoring clinical response to antimicrobial treatment in horses with bacterial pneumonia

Abstract Background Serum amyloid A (SAA) is a major acute phase protein in horses which could be a useful tool for assessing clinical response to treatment of bacterial pneumonia in adult horses. Objectives To monitor SAA concentration in response to treatment and identify associations among SAA concentration, WBC and neutrophil counts, and fibrinogen in bacterial pneumonia in adult horses. Animals Eighteen adult horses with bacterial pneumonia. Methods Prospective clinical study. Horses hospitalized with bacterial pneumonia were enrolled and SAA concentration and vital signs were assessed daily. SAA concentration was measured by a handheld meter. CBC and plasma fibrinogen were assessed on days 0, 1, and 2, then every 3 days until discharge. Data were not normally distributed and therefore were log transformed. Log‐transformed data were analyzed and comparisons were performed on LSMeans by the 2‐sided Student's t‐test at the 5% level of significance. Results Geometric mean SAA concentration on day 0 was 537 μg/mL (SE 383 μg/mL). Geometric mean SAA concentration decreased significantly over time (P = .0001), peaking at day 2 (geomean 1038 μg/mL, SE 261.7 μg/mL) and decreasing until discharge. Plasma concentration of fibrinogen (P = .06), neutrophil count (P = .48), and WBC count (P = .07) did not change significantly over time. Conclusions and Clinical Importance SAA concentration decreased significantly over the course of treatment and correlated with clinical improvement of pneumonia whereas fibrinogen, neutrophil, and WBC counts did not.