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

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.