The use of serum paraoxonase‐1 to assess inflammation in horses with colitis.

Background: Paraoxonase‐1 (PON‐1) has been suggested as a marker of inflammation and oxidative stress in horses and could potentially be used for prognostication in horses with colitis. Objectives: Assessment of PON‐1 in horses with colitis and comparison of two methods. Methods: Serum PON‐1 was measured by two methods (paraoxon and p‐nitrophenyl acetate) in 161 horses with colitis and 57 controls. Follow‐up samples obtained during hospitalization were available from 106 horses with colitis. The two methods were compared. Results: Serum PON‐1 was significantly lower in horses with colitis than in healthy horses (P <.0001 for both methods) as well as in nonsurvivors compared with survivors (P =.0141 [paraoxon‐based method] and P <.0001 [p‐nitrophenyl acetate‐based method]), but with marked overlap between groups. PON‐1 activity did not change parallel to a change in inflammatory status in response to treatment when assessed at admission and in up to seven follow‐up samples. Admission PON‐1 activity could not reliably classify horses as survivors or nonsurvivors, with sensitivity and specificity ranging between 53.1% and 72.9%. Results from the two methods were comparable. Conclusions: Both methods reliably measured serum PON‐1 activity. Significant differences in PON‐1 activity were found between healthy horses and horses with colitis and between survivors and nonsurvivors. However, PON‐1 activity varied considerably within groups. Both the proposed reference intervals as well as alternative cutoff values resulted in suboptimal diagnostic and prognostic performance, and the use of serum PON‐1 in horses with colitis thus seems to add little to existing diagnostic and prognostic markers. [ABSTRACT FROM AUTHOR]