Comparison of inulin with urea as dilutional markers of bronchoalveolar lavage in healthy and heaves-affected horses

Solute analysis in bronchoalveolar lavage fluid involves the use of dilutio nal markers to correct for variable recovery of pulmonary epithelial lining fluid (PELF). Urea is the best characterised endogenous marker, whereas in ulin appears to meet the requirements of an exogenous marker. In horses, th e use of inulin has never been investigated and the impact of lower airway diseases such as heaves, on PELF recovery is unknown. In this study, five h ealthy and five heaves-affected horses underwent airway endoscopy and bronc hoalveolar lavage. PELF recovery from bronchoalveolar lavage was calculated by the inulin and the urea method. The inulin method was compared to the u rea method and differences between healthy and heaves-affected horses were analysed. From a technical and analytical point of view, inulin fulfilled t he requirements of a marker of dilution as well as urea. When both healthy and heaves-affected horses groups were pooled together, PELF recovery calcu lated by the inulin method was significantly higher than by the urea method (6.43 +/- 4.08% versus 0.789 +/- 0.299%, P < 0.005). No significant differ ences were observed between healthy and heaves-affected horses, neither by the inulin nor by the urea method. Inulin did not present major advantages over urea, but the combined use of both markers can improve the standardisa tion of studies comparing PELF compounds, by providing upper limits (inulin dilution) and lower limits (urea dilution) of PELF recovery.