Serum Surfactant Protein D and Haptoglobin as Potential Biomarkers for Inflammatory Airway Disease in Horses

BACKGROUND The identification of serum biomarkers of lung inflammation would facilitate the diagnosis of inflammatory airway disease (IAD) in horses. HYPOTHESIS Horses with IAD have higher serum concentrations of markers of inflammation compared to controls. ANIMALS Twelve horses with IAD and 10 control horses. METHODS This was a prospective case-control study. Blood and BALF were collected from horses with IAD and controls. Serum concentration of surfactant protein D (SP-D), haptoglobin, serum amyloid A (SAA) and of the soluble form of triggering receptor expressed on myeloid cells 1 (sTREM-1) was measured using commercial ELISA tests. RESULTS Horses with IAD had higher serum concentration (log-transformed values) of SP-D (mean ± SD: 1.773 ± 0.51), haptoglobin (6.657 ± 0.202) and SAA (0.128 ± 0.396) compared to controls (0.942 ± 0.226, 6.38 ± 0.22, -0.398 ± 0.319, respectively; P < .01 for all). Furthermore, the concentrations of SP-D and haptoglobin combined allowed differentiating the 2 groups (IAD: 8.43 ± 0.564, controls: 7.322 ± 0.249, P < .0001) with a sensitivity and specificity of 100% when a cut-off of 7.70 (log value) was employed. CONCLUSIONS AND CLINICAL IMPORTANCE Surfactant protein D and haptoglobin serum concentrations could be a diagnostic aid in IAD. Further studies are necessary to establish the specificity of our findings before they can be applied in everyday practice.