Effect of sample storage on blood crossmatching in horses.

Background: Blood samples banked for up to 1 month are typically used to perform pretransfusion testing in humans and small animals, but this has not been validated using blood from horses.

Hypothesis: Compatibility of equine blood samples is repeatable using fresh samples, and reproducible using donor blood samples stored for up to 4 weeks.

Animals: Six healthy adult horses.

Methods: Randomized, blinded experimental study. Immunologic compatibility of the blood of all horses was assessed using a major and minor saline agglutination and hemolysin crossmatch using blood samples refrigerated for 0-4 weeks and fresh blood from the same horses. Crossmatch results were scored and then compared to identify changes of compatibility in each of the 4 tests. In addition, repeatability of the crossmatch technique itself was assessed by performing 6 iterations of this procedure in immediate succession with fresh blood from 3 horses.

Results: No significant difference in crossmatch results was found using fresh blood (P = .39-1.00). Reproducibility was poor using blood stored for 1-4 weeks, especially in tests using stored erythrocytes (major antigen crossmatches), with significant differences from baseline at all weeks (P < .05); 13 of these differences were positive, indicating poorer compatibility.

Conclusions and clinical importance: Equine blood crossmatching is repeatable using fresh blood, although decreased apparent compatibility after storage makes exclusion of compatible donors more likely than mistaken administration of incompatible blood. These data suggest that fresh samples should be collected from potential donors before crossmatching equine blood.