Agreement of stall-side and laboratory major crossmatch tests with the reference standard method in horses.

BACKGROUND:Crossmatching is used to prevent life-threatening transfusion reactions in horses. Laboratory methods are laborious and technically challenging, which is impractical during emergencies. HYPOTHESIS/OBJECTIVES:Evaluate agreement between a stall-side crossmatch kit (KIT) and a laboratory method (LAB) in horses with known and unknown blood types. ANIMALS:Twenty-four blood-typed and alloantibody-screened healthy adult horses (Aim 1) and 156 adult horses of unknown blood type (Aim 2). METHODS:Prospective, blinded study. Expected positive (n = 35) and negative (n = 36) crossmatches among 24 antibody and blood-typed horses were used to determine sensitivity and specificity of KIT and LAB against the reference method. Agreement in 156 untyped horses was evaluated by reciprocal crossmatch (n = 156). RESULTS:Sensitivity (95% confidence interval [CI]) for LAB and KIT compared with expected reactions was 77.1% (59.9%-90.0%) and 91.4% (77.0%-98.2%), and specificity 77.8% (60.9%-89.9%) and 73.5% (55.6%-87.1%), respectively. The KIT was 100% sensitive for Aa reactions; LAB was 100% sensitive for Qab; and both were 100% sensitive for Ca. Cohen's κ agreement for LAB and KIT with expected positive and negative reactions (n = 71) was moderate (0.55 [0.36-0.74]) and substantial (0.65 [0.47-0.82]), respectively. Agreement was fair comparing LAB with KIT in Aim 1 (0.30 [0.08-0.52]) and in untyped horses in Aim 2 (0.26 [0.11-0.41]). CONCLUSIONS AND CLINICAL IMPORTANCE:Agreement between KIT and LAB with expected reactions was blood type dependent. Performance of both methods depends on blood type prevalence.