Transfusion Medicine Myths

Ladan Mohammad-Zadeh, DVM, DACVECC, lists some common blood transfusion myths, then explains the true or false reasons for these myths.

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storage of packed red blood cellsTransfusion medicine has greatly evolved since the discovery of canine blood groups in 1910. Today, there are about a half dozen erythrocyte antigens that are clinically significant in canines, the most important of which are DEA 1.1, 1.2 and 4. Cats have a much simpler AB blood group system. As our knowledge of transfusion medicine has grown, we have updated our practices and standards in protocol for processing and administering blood products. Consequently, some myths have developed based on outdated concepts or lack of understanding of blood group physiology which have now been better clarified. Here are a few such myths:

Packed RBCs must be diluted with saline prior to administration.


This could actually be true or false depending on how the unit was processed. Prior to the addition of a preservative in packed RBC units, the PCV of a unit could easily be over 70%. Blood with a PCV over 70% is hyperviscous and could be detrimental when administered quickly, especially to a hypovolemic or dehydrated patient. However, the additional volume of the preservative dilutes out the unit so the final product is safe to administer as is. If you are in doubt, you can easily check the PCV of the unit prior to administration.

Pregnancy in canines makes them ineligible to be blood donors.


Prevalence of alloantibodies in multiparous dogs is the same as nulliparous dogs, meaning there is no increased risk of a recipient experiencing a transfusion reaction when receiving blood from a multiparous dog.

Cats do not need to be blood typed prior to transfusion.


Similar to humans, cats do have naturally occurring antibodies, and in the event that a type B cat is given type A blood, it could prove fatal. Although the majority of American Domestic Shorthair cats are Type A, the prevalence of Type B cats is not as rare as it used to be. With the recent discovery of another blood antigen, Mik, it is clear we have not learned all there is to know about feline blood types. Some recommend cross matching even with the first blood transfusion in a cat.

Cross match is necessary if a blood product is given more than three days from the previous transfusion.


It takes about 3–4 days to develop antibodies against RBC antigens. Thus, a unit from a donor that may have been compatible for the first transfusion may no longer be compatible after three days.

A Hemonate ™ filter should be used to reduce the possibility of bacterial contamination.


A standard Hemonate ™ filter pore size is 18 micrometers. The average size of a bacterial particle is 1 micrometer. Thus, the primary reason for using any filter, Hemonate ™ or Y–filter (170 microns), is to prevent large particulates (cellular or protein aggregates) from entering the blood stream. A Hemonate ™ filter can only be used to filter volumes up to 60ml.

Blood Product Quick Facts

Packed RBC (10 ml/kg): Acute blood loss, IMHA, chronic blood loss anemia

Fresh Frozen Plasma (10 ml/kg): Non–platelet associated coagulopathy (DIC, rodenticide, liver failure), albumin replacement if given in volumes >10ml/kg

Platelet Concentrate (1 unit/ 10 kg): Critically thrombocytopenic patient (<50,000) undergoing surgical procedure, or ongoing clinical hemorrhage from thrombocytopenia

Fresh Whole Blood* (20 ml/kg): Acute whole blood loss, thrombocytopenia.
*Stored whole blood cannot be used to treat thrombocytopenia

Cryoprecipitate (1 unit/10 kg): Factor VIII deficiency, VonWillebrands disease

1. Callan et al., Canine platelet transfusions. 2009. JVECCS. 19:401–415.
2. Blais et al., Canine dal blood type: A red cell antigen lacking in some dalmations.2001. JVIM. 21:281–286.
3. Blais et al. Lack of evidence of pregnancy–induced alloantibodies in dogs. 2009. JVIM. 23:462–465.
5. Small Animal Critical Care Medicine. Silverstein & Hopper ed., Saunders. St. Louis, MO. 2009.
6. Veterinary Hematology. Feldman BF ed. Fifth edition. Lippincott Williams, Baltimore, MD. 2000.
7. Weinstein et al., A newly recognized blood group in domestic short hair cats: The mik red cell antigen. 2009. JVIM. 21:287–292.

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