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.Journal of Vete… 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.Journal of Vete…+1 Type A cats carry weak or absent anti-B alloantibodies, but A-B mismatches in either direction are unacceptable.Journal of Vete…+1 Type AB cats should receive AB-type blood; when unavailable, washed type A blood is the alternative to minimize minor reactions.Journal of Feli…

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.Veterinary Clin…+1 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.Journal of Vete…+2 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.Journal of Feli…+1 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.Journal of Vete…

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.Journal of Feli… Anti-FEA 1 alloantibodies appear as early as 5 days post-transfusion and remain detectable for over 400 days.Journal of Feli… Post-transfusion alloimmunization occurs in 25% of feline recipients transfused with AB-compatible blood.Journal of Feli… Previously transfused cats with a positive major crossmatch have a lower rate of expected hematocrit increase (40%) compared to those with a negative major crossmatch (56.5%).Journal of Feli…

Three crossmatch methods are available, with antiglobulin-enhanced techniques detecting the most incompatibilities. The antiglobulin-enhanced gel column (AGC) crossmatch detects all A-B mismatches plus 14 additional non-AB incompatibilities not identified by the standard gel column method.Journal of Vete… The in-clinic AFG-enhanced immunochromatographic strip is simple to perform and interpret but is less sensitive for weaker incompatibilities — the odds of detecting an incompatibility increase 2.9-fold with each unit increase in incompatibility grade on standard tube crossmatch, and 6.1-fold with each unit increase on AFG-enhanced tube crossmatch.Veterinary Clin… The minor crossmatch is negative in all cases in one serial crossmatch series, making the major crossmatch the critical component.Journal of Feli…

In genuine emergencies where crossmatching is not feasible, AB typing alone is the minimum acceptable standard, with the understanding that non-AB incompatibilities will go undetected.Journal of Vete… Mik typing is not clinically available due to lack of typing reagent, making crossmatching the only practical method to detect anti-Mik alloantibodies.Journal of Vete…+1

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