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Transfusion medicine has greatly improved our ability to treat anaemia in human and veterinary medicine. The safety and efficacy of transfusion medicine has advanced as both our understanding of the relevant biological systems has improved and as our tools and procedures for carrying out transfusions have become more sophisticated. This dissertation reports on two prospective clinical studies examining specific aspects of feline pre-transfusion testing methods with the potential to improve the safety and efficacy of the subsequent transfusions.
In the first study, the novel immunochromatographic point-of-care blood typing device (RapidVet-H IC Feline, DMS Laboratories) for the feline AB blood group system was assessed for reliability by comparing it to two other tests as reference methods, the Pennsylvania tube agglutination and a gel column test. Blood samples from 105 sick and healthy cats were included. The samples were between 0 and 10 days old (median 3 days) and were tested for haemolysis and agglutination; the haematocrit ranged from 0.07 to 0.57 l/l (median 40 l/l). The reference methods showed a 100% agreement with each other. 85 samples were determined blood type A by the two reference methods, 80 of which were correctly identified by the immunochromatographic test. Four were misidentified as AB and one was rated inconclusive. All B samples were correctly typed. Two of the three AB samples were correctly identified by the immunochromatographic test and one was rated inconclusive. The sample quality had no influence on test performance. Of 30 repeats, 28 were readable and showed agreement in 27 cases. The agreement of the immunochromatographic test with the control methods was 96.1% for the 103 conclusive tests, and it showed high sensitivity and specificity for A and B antigen detection, of note being the 100% sensitivity for B antigen detection. Based on the data, it is still suggested that AB results be reconfirmed with a laboratory method and that a 'back-typing' be performed with plasma from B-typed samples, ensuring that cats with blood type B not be given A-type blood. The novel immunochromatographic test device showed very good performance and ease of use, as well as convenient storage requirements.
The second study was designed to detect a positive cross-match in cats after receiving an AB-compatible blood transfusion, potentially indicating that alloimmunisation had taken place in those patients. Twenty-one hospitalised anaemic recipients (blood type A: n = 20; blood type B: n = 1) received 1-4 (median 2) whole-blood transfusions over 1-6 days (median 2 days) in 33 transfusion instances. The manual laboratory tube cross-matching method, including major, minor and recipient control, was used to serially test transfusion patients for macroscopic and microscopic agglutination reactions. No clinical signs of an acute transfusion reaction were observed. A total of 63 cross-matches were performed. The minor cross-match was negative in all cases. A positive major cross-match was observed in five cases after 2-10 days (median 5 days) after an initial blood transfusion. These five cats had received a total of 1-4 (median 2) blood transfusions. In 51.5% (17/33) of transfusion instances, the cat's haematocrit increased as expected, with cats with a positive major cross-match at 40% (4/10) vs 56.5% (13/23) if the major crossmatch was negative. The five positive major cross-match results likely represent feline recipients which developed alloantibodies as early as two days after the initial blood transfusion. Cross-matching is currently only recommended as part of pre-transfusion testing for repeat transfusions in cats four days after having received an initial transfusion. The second study adds data to an evidentiary basis for recommendations to include cross-matching in routine pre-transfusion screening tests.
Both studies contribute to an increased awareness of ways to improve patient safety for cats receiving allogeneic blood and blood products.