Blood transfusions are a critical tool in small animal practice, but they must be used with clear clinical justification. In our recent webinar, Blood Transfusions – When, How and Why, Simon Tappin, in collaboration with Pet Blood Bank and ManyPets, explored when transfusions are indicated, which products to use, and how to administer them safely.

Simon walked us through the differences between whole blood, packed red cells, plasma products, and platelet-rich plasma, and shared tips for practical transfusion planning, particularly in high-risk surgeries. He also discussed considerations such as autotransfusion, volume overload, and product compatibility.

The session also featured a wide-ranging Q&A, shedding light on key clinical dilemmas and best practices.

When and Why to Transfuse

Not every anaemic patient requires a transfusion. Simon emphasised that while transfusions are generally safe, they should only be administered when there's a clear expected clinical benefit—such as increasing oxygen-carrying capacity or delivering essential clotting factors.

In cases where the risks (e.g. transfusion reactions, volume overload, particularly in cats or patients with heart disease) outweigh the benefits, restraint is warranted. Simon cited evidence from human medicine indicating that patients who received restrictive transfusions—just enough to meet their physiological needs—had better outcomes than those given transfusions to normalise values like PCV.

What Blood Products Are Available?

The webinar gave an excellent overview of available blood products, including:

• Whole blood – ideal for significant acute haemorrhage

• Packed red blood cells (pRBCs) – useful for anaemia without the need for plasma volume

• Plasma (fresh frozen and frozen) – for clotting factor support

• Cryoprecipitate – for specific clotting deficiencies

• Platelet-rich plasma – less commonly used, but available for thrombocytopaenic patients

Simon also touched on how and when each product is most effectively used in clinical practice.

Q&A with Simon Tappin

1. When, if ever, should a blood transfusion be avoided in animals?
Whilst transfusions are considered very safe, and often lifesaving, there are of course some risks, so are not something that we would give to a patient without there being a clear expected benefit (so an increase in oxygen-carrying capacity in a severely anaemic patient or clotting factors to halt bleeding etc). So as with any treatment, we need to clearly weigh up the pros and cons of giving it. There are risks with transfusions (reactions [especially when transfused previously], volume overload [especially in cats and patients with congestive heart failure], etc), so we would want to expect an improvement to overcome and have a positive impact. There’s a nice study in human medicine looking at outcome of patients that were transfused liberally to normalise their PCV and those that were transfused restrictively to just what they needed. The restricted patients had a better outcome, outlining that we should only use transfusion products when we need to rather than to normalise blood results.

2. If you are wanting blood "hanging" just in case (for a planned very high-risk surgery), do you use packed cells alone, resuspend packed cells immediately prior to use, or just two IV lines—one with saline and one with packed cells?
Depends on what you have available. In major blood loss, for example secondary to a large vascular resection or an adrenalectomy, whole fresh blood would be ideal. If you have packed cells, I’ve used these straight and wouldn’t be resuspending them. If you need to also give saline (or balanced crystalloids), then this can be given through a separate catheter (remembering not to mix calcium-containing fluids with the blood products). You could also give plasma, depending on blood loss, if you needed to, which would recreate the components of whole fresh blood.

3. How would you go about transfusing a bitch spay that has bled shortly after the operation? And how is that different from, say, a ruptured splenic haemangiosarcoma?
I think you’d approach the two in the same way. Apply abdominal pressure if possible, ascertain if the bleed is surgical, stabilise the patient haemodynamically as much as possible before anaesthesia, and then correct at surgery. The tricky part is stabilising haemodynamically whilst there is ongoing bleeding. Autotransfusion can be helpful here, as can trying to minimise the amount of transfusion product that’s given until the bleeding is stopped. However, practically this is tricky and you often need to use some blood products in that stabilisation phase (depending on the severity of the bleed).

4. For a full cross-match, where is the best place to send it assuming we can get the aliquots from PBB for a second transfusion?
Sending blood to an external lab will be the best way forward, as they will be able to wash the cells more effectively and thus get a more accurate cross-match and idea of compatibility. In the UK, Pet Blood Bank will usually (depending on availability) be able to supply aliquots of held blood to cross-match against your patient. This does take a little time (around 24 hours, sometimes quicker), so planning this when a second transfusion is needed would definitely be advised.

5. Just to clarify, if we have an AB cat can they receive both A and B blood? And if so, can they also donate to both A and B cats?
AB cats have both the A antigen and the B antigen on the surface of their red cells. Thus, they don’t have antibodies against either circulating. You can transfuse them with A or B blood, but we usually use A blood given it’s easier to find A donors. Once we have transfused them, we usually then stick to that blood type. You cannot give AB blood to either A or B cats as they have both antigens on the surface, meaning they will interact with any preexisting antibodies (almost all B cats have Anti-A antibodies), and if not, the immune system will destroy the cells more quickly given the presence of the other antigen.

If you missed the live session or want to dive deeper, you can access the full webinar recording here:
👉 Blood Transfusions – When, How and Why

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