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Compatibility Test

  • Group typing: In the case of the feline species especially and in dogs after the second transfusion, it is important to know the blood group of both the donor and the recipient. Currently we can find several commercial kits on the market that allow us to determine whether a dog is positive or negative for the DEA-1.1 antigen, as well as knowing the blood group of a cat. In dogs, it must be known before a transfusion whether the donor and recipient are positive or negative for the DEA-1.1 group. In cats, the blood group must always be determined before a transfusion to avoid adverse reactions and, in pregnant females, to prevent neonatal isoerythrolysis.

  • Cross-compatibility tests or crossmatching: These tests are not aimed at detecting what type of antigen is in the erythrocyte membrane, but rather demonstrate the serological compatibility between donor and recipient, demonstrating the presence of natural or induced alloantibodies in the serum. These alloantibodies could cause hemagglutination or hemolysis reactions against other known blood groups or other erythrocyte antigens. The degree of agglutination is expressed from 1+ to 4+.


Major compatibility tests assess the presence of alloantibodies in the recipient's plasma against the donor's cells. This test is very useful because it will help us predict whether the donor's transfused cells will be attacked by antibodies in the recipient's plasma, causing a transfusion reaction. If hemolysis and/or agglutination occurs in major tests, the transfusion cannot be performed, since the recipient has alloantibodies against the donor's erythrocytes. Minor compatibility tests, on the other hand, demonstrate the existence of alloantibodies in the donor's plasma against the recipient's erythrocytes. If this test were to be incompatible, it would not be so important because the amount of donor serum is small, especially if we use concentrated red blood cells and it is also diluted in the patient's serum. In any case, if we perform the transfusion the patient will have to be closely monitored.


In dogs, it is possible to omit performing these tests before the first transfusion due to the absence of natural alloantibodies. However, it is mandatory in future transfusions, despite being from the same donor or blood group.

In the feline species, cross-compatibility tests are necessary before the first transfusion given the presence of natural alloantibodies. What's more, only with these tests can we predict the blood group of the donor and recipient. If the major compatibility tests are strongly incompatible, the recipient cat is likely to be type B and the donor A (or AB). If the minor match is strongly incompatible, the donor cat is likely to be B and the recipient is A (or AB). Furthermore, in the case of feline species and due to the presence of powerful anti-A agglutinins, it is possible to recognize blood incompatibility between two patients with a simplified cross-compatibility test, placing a drop of blood from the donor and the recipient in a ported at room temperature. If hemagglutination appears in less than a minute, it shows two animals from different groups.


There are already commercial kits on the market to perform these cross-compatibility tests.

Instructions for performing major crossmatching:

  1. Centrifuge the donor blood in EDTA for 10 minutes at slow speed, in order to prevent the sample from hemolyzing.

  2. Pipette 0.2ml of the blood sediment and mix it well with 4.8ml of 0.9% NaCl.

  3. Pipette 0.1ml of the resulting sample into 3 different tubes.

  4. Add 0.1 ml of recipient serum or plasma to each tube.

  5. Let one tube incubate for 15 minutes at room temperature, another at 37ºC and the last at 4ºC.

  6. Centrifuge all tubes for 1 minute at high speed.

  7. Observe if there is hemolysis in the supernatant. If it existed, the test would be positive and the animals would be incompatible.

  8. Examine a drop of blood sediment under a microscope; if we see microagglutination, there is cross-incompatibility.


The steps to do a minor crossmatch are identical to those of the major one, with the difference that we must mix plasma or serum from the donor with red blood cells from the recipient.


Patient selection and extraction.

The ideal donor animal must meet the following conditions:

  • That he is a young adult, well vaccinated and dewormed.

  • Who has never received a transfusion.

  • With a weight greater than 20-25kg in dogs and 4kg in cats.

  • They must be dogs negative for Leishmania, Erlichia, Filaria, Babesia and Anaplasma or cats negative for FeLV, FIV, PIF, Toxoplasma and Filaria.

  • That the blood count and blood biochemistry values are normal.


In dogs, it is generally not necessary to sedate them to perform the extraction. The best vein to perform the extraction is the jugular vein. Blood is collected in human medicine blood collection bags, which contain 63ml of CPD-A (citrate-phosphate-dextrose-adenine), with the capacity to store 450ml of blood. Throughout the extraction the bag must be shaken for correct homogenization and we will keep it below the patient so that the blood descends by gravity. This blood can be passed through filters to remove leukocytes and reduce febrile reactions.

In the case of cats, there are no collection bags marketed in our country adapted to small amounts of blood. For this reason, blood is normally drawn in 20 ml syringes, also from the jugular vein, using a butterfly valve. To these syringes we will add, as an anticoagulant, sodium heparin (at a rate of 5-10 IU per ml of blood), CPDA or 3.8% citrate (1ml of anticoagulant per 9ml of blood).

In the canine species, extractions can be performed every month (20ml/kg), in cats only 10ml/kg monthly.

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