What is the clinical protocol for blood typing and crossmatching prior to transfusion in dogs and cats?

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Blood typing is mandatory before every transfusion in both species; crossmatching requirements differ by species and transfusion history. --- In dogs, DEA 1 typing is the minimum pretransfusion requirement. Seven canine blood groups are recognized (DEA 1, 3, 4, 5, 6, 7, and 8), plus the more recently described Dal, Kai 1.1, and Kai 1.2 antigens.3 DEA 1 is the most clinically important due to its strong antigenicity and near-equal distribution of DEA 1-positive and DEA 1-negative dogs across many breeds.3 Dogs are generally considered to lack clinically important naturally occurring alloantibodies, with the possible exception of anti-DEA 7, meaning a first transfusion in a typed, never-previously-transfused dog carries lower immunologic risk than in cats.3 Crossmatching in dogs is required — not optional — in specific circumstances. A crossmatch is indicated when transfusion history is unknown, when a prior transfusion was given more than 4 days before the current one, or following a hemolytic transfusion reaction.3 Even when DEA 1-matched blood is used, crossmatch incompatibilities have been detected 26 days after transfusion, indicating alloantibody formation against non-DEA 1 antigens; crossmatching is therefore required after any first transfusion even when DEA 1 typing was performed.3 Major crossmatch incompatibilities occur in 17% of transfusion-naïve dogs when tested against a panel of donors, though all dogs in that cohort were compatible with at least one of three potential donors.5 Dogs receiving crossmatch-compatible blood had a significantly greater post-transfusion hematocrit increase (12.5 ± 8.6%) compared to dogs transfused without crossmatching (9.0 ± 4.3%).5 Given the potential for immediate or delayed hemolytic reactions and shortened RBC lifespan, crossmatching all dogs prior to transfusion is recommended when possible.5 In cats, AB blood typing is essential before every transfusion. The AB system is the major feline blood antigen system, with type