Saturday, November 11, 2017

Blood Transfusions in Cats


Most people have some familiarity with the concept of a blood transfusion, perhaps by donating blood to the local Red Cross, or possibly as a recipient during a hospital stay.  Thankfully, most cat owners have very little experience with transfusions when it comes to their cat.  Transfusions are infrequently performed in general veterinary practice, however, as cat owners become more willing to pursue state-of-the-art veterinary diagnostics and therapeutics for their beloved companions, advanced procedures such as blood transfusions are becoming more commonplace. 

Topeka, our hospital cat and blood donor.
There are several reasons why a cat might require a transfusion, with anemia (a decreased amount of red blood cells) being by far the most common.   Some veterinary clinics have a pet “hospital cat” that lives at the clinic and earns its keep by occasionally functioning as a blood donor in those rare times of need.  For years, my hospital employed “Topeka”, a black and white domestic shorthaired cat who, besides providing us with years of joy and affection, saved many lives by donating her red blood cells to desperately anemic fellow felines.

Blood donors should be healthy adult cats of agreeable temperament (for easy handling and restraint), preferably in the age range of 2 to 8 years.  Ideally, the cat should weigh 5 kg (11 lbs) or more, be shorthaired, and be of lean body stature.   The donor’s PCV (packed cell volume, a measure of the percentage of the blood that is comprised of red blood cells) should be greater than 35%. (The normal range for a typical cat is 29 to 48%.)  The cat should test negative for the feline leukemia virus (FeLV), the feline immunodeficiency virus (FIV), toxoplasmosis, and mycoplasmosis (a red blood parasite).  Blood should not be collected more than once every 4 to 6 weeks from an individual donor.  

In a general practice setting like my own, transfusions are performed using whole blood, because that’s what we obtain from Topeka, our donor.  However, the ability to fractionate whole blood into its component products has made it easier to treat a variety of conditions if a blood donor isn’t readily available.  Veterinarians now have access via veterinary blood banks, local emergency clinics, or referral centers, to fresh or stored whole blood, packed red blood cells (pRBCs), fresh-frozen plasma (FFP), and platelet products. 

Blood is sterilely collected into commercially prepared blood bags containing an anti-coagulant.  The blood can be used immediately, or it can be stored in a refrigerator for several weeks until needed.  As noted above, fresh whole blood can also be separated into its component parts.  Whole blood contains everything: red blood cells, serum proteins, clotting factors, and platelets.  Because the most common reason for a transfusion is severe anemia, packed red blood cells (pRBCs) may be a more appropriate product.  The advantage of using pRBCs is that you are administering the same amount of red blood cells as that found in a unit of whole blood, but it is in a much smaller volume, making it safer for animals with concurrent heart or kidney disease. 

Cats have specific blood types, similar to humans: Type A, Type B, and Type AB.  Unlike humans, there are no type O cats.   The majority (99%) of cats in the United States are type A.  Type B is less common.  In Europe, Japan, and Australia, higher percentages of cats with Type B blood are found.  Some breeds of cats (for example: British shorthair, Devon rex, Cornish rex, exotic shorthair, Abyssinian, Japanese bobtail, Persian, Himalayan, Somali, and sphinx) have a higher percentage of Type B blood.  Although purebred cats are most likely to be Type B compared to non-purebred, it is interesting to note that Siamese cats are reported to be 100% Type A.  Cats with blood Type AB are extremely rare.  In 29 years of veterinary practice, and having performed countless blood typing procedures, I have still not encountered a type AB cat. 

The Rapid Vet H Blood Typing Test.  Both cats here are Type A.
Transfusing blood products into a cat isn’t a benign procedure.  The feline immune system can react dramatically to blood components, with life-threatening consequences.  The serum of cats with Type A blood possesses antibodies that react against Type B red blood cells.  Conversely, the serum of cats with Type B blood possesses antibodies against Type A red blood cells.  In Type A cats, the amount of antibodies they have against Type B blood is relatively low, so accidentally giving Type B blood to a Type A cat will typically result in a mild reaction, with the transfused Type B red blood cells undergoing attack and destruction by the immune system of the recipient within 2 to 3 days.  However, the amount of anti-A antibodies in the blood of a Type B cat is very high, and administering even a small amount of Type A blood into a Type B cat can cause acute, dramatic destruction of the transfused red blood cells, resulting in a potentially fatal transfusion reaction.  It is therefore imperative that blood typing be performed before any transfusion is undertaken.  To be even safer, it is advisable to perform an additional procedure called crossmatching to further minimize the risk of a transfusion reaction.  A detailed description of crossmatching is beyond the scope of this article, but it involves mixing donor red blood cells with serum of the recipient (major crossmatch) and mixing donor serum with recipient red blood cells (minor crossmatch) and observing the reaction.


Once the compatibility of the donor and the recipient has been confirmed, the transfusion can be performed.  Initially, the blood should be administered slowly.  If no adverse effects are witnessed after 30 to 60 minutes, the rate of administration can be increased.  The rate depends on the urgency of the cat’s condition.  Cats that are in shock from acute blood loss require rapid blood administration.  Cats with cardiac disease are at risk of fluid overload and congestive heart failure, and may require a much more judicious rate of administration. A typical transfusion is completed in 4 to 6 hours.  The goal of the transfusion, in most cases, is to increase the patient’s PCV sufficiently to reverse the signs of anemia.  A reasonable aim is to achieve a PCV of 20%, although this isn’t always possible.

My beloved Crispy
[I have personal experience with blood transfusions not only as a veterinarian, but as a cat owner. Two years ago, my 14 year-old cat Crispy underwent surgery to remove an intestinal tumor.  Immediately post-surgery, Crispy became alarmingly pale and was very slow in waking from anesthesia.  A quick in-house test revealed a dangerously low red blood cell count (PCV of 12%) and a transfusion was going to be needed if she was going to have any chance of recovery.   Although 99% of domestic shorthaired cats in the U.S. are Type-A, I quickly checked Crispy’s blood type right after surgery, and to my shock and dismay, she was a very definite Type B.  Frantic calls to the first two nearby emergency clinics were futile; they only had Type A blood on hand.  Miraculously, the third referral center had two units of Type B packed red blood cells stored in their refrigerator.  A harrowing 20-minute taxi ride ensued, with my anesthetized cat on my lap, her endotracheal tube still in her windpipe.  Thankfully, the emergency staff was ready and waiting, and her transfusion began immediately upon arrival.  She woke up from anesthesia a tense 40 minutes later.  (Catnip subscribers may remember this case, which I described in detail in the article “When Doctor Becomes Client” in the July 2015 issue of Catnip). ]

Although blood transfusions are infrequently performed in general practice, the increased availability of feline blood and blood products and the willingness of cat owners to pursue more advanced care for their pets has made this often life-saving procedure more common.  By transfusing a patient only with the blood component that is needed, knowing the blood types of the donor and recipient, and performing a crossmatch right before the transfusion, most transfusions can be performed safely and effectively.


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