Effects of Blood Contamination on Peritoneal D-Dimer Concentration in Horses with Colic

Background: Peritoneal D-Dimer concentration can be determined to assess peritoneal fibrinolysis activity in horses with gastrointestinal disorders. However, blood contamination of peritoneal fluid may occur during collection and could alter peritoneal D-Dimer concentration.
Hypothesis/Objectives: Blood contamination in peritoneal fluid does not affect interpretation of peritoneal D-Dimer concentration in horses with colic.
Animals: Thirty-four horses with colic and 4 healthy horses.
Methods: Peritoneal fluid and blood samples were simultaneously collected upon admission. Then, peritoneal fluid was serially contaminated with the horse's own blood; final contaminations corresponded to 1, 5, 10, and 20% of blood in peritoneal fluid. D-Dimer concentration was determined in blood, peritoneal fluid, and contaminated peritoneal fluid samples. Data were analyzed using a longitudinal linear model and a generalized estimating equations analysis to assess the quantitative and qualitative variations of the effect of blood contamination on peritoneal D-Dimer concentration.
Results: Peritoneal D-Dimer concentration was only quantitatively affected when peritoneal fluid was contaminated at 20% of blood. However, when using increasing cut-off values of peritoneal D-Dimer concentration (100, 2,000, 8,000, and 16,000 ng/mL), this effect disappeared at the highest cut-off values (8,000 and 16,000 ng/mL). When peritoneal fluid contamination was grouped as "minimally contaminated" (≤1% of blood) and "highly contaminated" (≥5% of blood), no significant differences on D-Dimer concentration between both groups at each cut-off value were observed.
Conclusions and Clinical Importance: Although quantitative results of peritoneal D-Dimer concentration could be affected by high levels of blood contamination (≥20%), interpretation of increased peritoneal fibrinolytic activity was not significantly affected.