what is the protocol for blood typing and crossmatching in cats prior to transfusion?

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AB blood typing is essential before every feline transfusion, and crossmatching is recommended before every transfusion — including the first — due to naturally occurring alloantibodies outside the AB system. AB typing is the non-negotiable first step. Immunochromatographic strip kits are as accurate as laboratory flow cytometry for AB typing and are suitable for in-clinic use.1 Type B cats carry strong anti-A alloantibodies in 12 of 13 cats tested, making A-to-B transfusion acutely and potentially fatally hemolytic — as little as 1 mL of type A blood can trigger anaphylactic shock in a type B recipient.111 Type A cats carry weak or absent anti-B alloantibodies, but A-B mismatches in either direction are unacceptable.111 Type AB cats should receive AB-type blood; when unavailable, washed type A blood is the alternative to minimize minor reactions.11 Crossmatching should be performed before every transfusion, not only repeat transfusions. The traditional threshold of crossmatching only when a second transfusion is given more than 4 days after the first is insufficient.56 Naturally occurring non-AB alloantibodies — including anti-Mik and anti-feline erythrocyte antigen (FEA) 1 — are present in transfusion-naïve cats and can cause acute hemolytic transfusion reactions despite AB compatibility.6710 The prevalence of non-AB crossmatch incompatibility in transfusion-naïve cats is 29% in one US population and 25% of previously transfused cats develop new alloantibodies as early as 2 days post-transfusion.36 Cats receiving crossmatch-compatible packed red blood cells show a significantly greater post-transfusion packed cell volume increase compared to cats receiving only AB-typed, non-crossmatched blood.6 For previously transfused cats, crossmatching is mandatory regardless of the interval since the last transfusion. Positive major crossmatch results develop as early as 2 days and up to 10 days (median 5 days) after a first whole blood transfusion.3 Anti-FEA 1 alloantibodie