Feline Anaemia
By E.G.D.McCarrison BVMS MRCVS
Anaemia in cats is not a diagnosis in itself but rather an indication of other disease processes taking place. These processes can range from acute blood loss to slow ongoing diseases such as chronic kidney failure. In order for your vet to be able to diagnose the cause of the anaemia he or she must first make a thorough assessment of your cat’s general health. This will usually involve a full clinical examination and a complete set of blood tests not only looking at the different types and relative amounts of red and white blood cells but also looking at the levels of many biochemical markers and electrolytes in the blood. From these results your vet should be able to determine what the initial diagnosis should be and, where possible, recommend a plan to treat the underlying cause of the anaemia.
The anaemia itself may not require individual treatment since correcting the cause may well allow the body to reverse the anaemia through natural processes; but in order to determine this it is necessary for the vet to know whether the anaemia is ‘regenerative’ or ‘non regenerative’. As these terms suggest, regenerative anaemia means that the body is already trying to correct the blood loss, whereas in non regenerative anaemia the normal processes of recovery are not working.
Anaemia is a condition where the number of circulation red blood cells is lower than that expected in a normal cat. The number of red blood cells is maintained by the body producing a regular supply of new cells to compensate for the red cells that are being destroyed either due to age, or disease conditions. Anaemia therefore can come about either by excessive destruction of the red cells or by the lack of production of new ones. This production of red blood cells, mainly from the bone marrow of the larger bones, is called erythropoiesis.
As a general rule regenerative anaemia tend to be caused by acute blood loss from injuries or infections, although long term and chronic low level blood losses from the bowel for example would also be regenerative - at least in the initial stages. Non regenerative anaemia are more likely to be due to chronic diseases such as kidney failure where the condition has been present for a long time and there are multiple complications building up due to the initial disease.
The mechanism to produce new red blood cells from the bone marrow as mentioned above is called erythropoiesis and in large part is controlled by a hormone called erythropoietin. This is produced by cells in the outer rim of the kidney whenever they sense a reduction in the amount of oxygen being carried in the blood. During the course of kidney disease these cells become damaged and as a result do not produce enough erythropoietin. This results in fewer red blood cells being produced at a time when, due to further complications from the kidney disease, it is thought that the life span of the red cells already present is reduced. You therefore get a double action of increased destruction and reduced production of the red blood cells. It is little wonder then that a cat with kidney failure is often going to have a severe anaemia with a poor appetite and be very lethargic.
The mainstay for treating anaemia in kidney failure cases in the past has been to ensure that there is enough iron available for haemoglobin production by giving vitamin B supplements, since a deficiency in these could cause a nutritional anaemia; and also giving anabolic steroids. There is little documented evidence that any of these are effective in stimulating erythropoiesis or improving anaemia.
It was because of this lack of effective treatments that, when I was recently treating Cotton, an 18 year old cat with multiple problems including kidney failure and diabetes mellitus, I felt compelled to try to find another treatment. Research eventually led me to a synthetic erythropoietin used in humans with anaemia. It had also been used in animals but I could find little evidence of it being used regularly in general practice for cats with chronic kidney failure. The next question was how safe was it to use in cats. It was known that whilst it was effective at stimulating erythropoiesis in animals it could also stimulate an antibody reaction, not only to the drug but also to the body’s own natural erythropoietin. If this was to happen then a serious condition could be made much worse.
Another problem that I initially encountered was finding a presentation of the drug in a realistic amount which was not going to be extremely expensive. Eventually I found a product called Neorecormon marketed by Roche which was sold in pre filled syringes and in various concentrations - one of which was exactly right for cats. It was even a stock item at the veterinary wholesalers.
As is often the case when dealing with illnesses you have to make a decision or judgement. If the treatment was to work, are the potential benefits of the treatment outweighed by the potential side effects? This particular cat was getting so lethargic and depressed that I felt it was worth trying. I made sure that the owner was fully aware of the risks, and with her consent we started the course of injections.
At least in this case the change was remarkable. Within 2 weeks the anaemia was improving and her appetite increased. There was a general improvement in the cat’s behaviour and her blood results improved tremendously. Before treatment started her haematocrit had dropped to a low of 13% the reference range for our in-house haematology machine for cats was 24-40%. Within 10 days of the first injection this had risen to 26.5% i.e. back to low reference range. Three weeks into treatment this had risen to 31.3%. The frequency of the injections was then reduced and the haematocrit kept in the low 30% range. Unfortunately the kidney disease was progressing and eventually this brave little cat had to be euthanased 6 weeks after starting the treatment for the anaemia. I am sure that Cotton’s quality of life improved with the improvement in her anaemia and, had I started the treatment for the anaemia earlier we could perhaps have made even more improvements to her life.
I was left wondering why I had not used this therapy before and whether other vets were using the erythropoietin as a regular treatment of non regenerative anaemia in cats? Subsequent questioning of other vets suggests that this is not being used regularly. The reason for writing this article is to raise this issue and to encourage others to examine this as a possible treatment strategy, particularly for chronic kidney failure which has anaemia as a significant secondary effect. This will obviously not be suitable in all cases but I believe it should be considered more often than it appears to be.
If your cat has anaemia then it is well worth asking your vet about this treatment. When it first became available in the uk it was very expensive, but it is much more affordable now.
E.G.D.McCarrison BVMS MRCVS
Footnote by Feline Friends:
The synthetic erythropoietin (rhEPO) referred to by Mr. McCarrison is provided by an artificially created DNA (Recombinant DNA), and has benefited humans with non regenerative anaemia since the latter part of the 1980’s.
In the mid to late 1990’s clinical trials took place in America using rhEPO on cats with CRF and serious non regenerative anaemia. Because the drug uses human DNA some cats developed antibodies to it, with the initially positive results being short lived and sometimes even worsening the anaemia.
The veterinary surgeon considering the use of rhEPO on a cat is therefore faced with somewhat of a dilemma. A cat with severe CRF related non regenerative anaemia will die of the anaemia. However, unless the cat develops an antibody reaction, the use of rhEPO will remove the anaemia and all its side effects; enabling both the vet and the cat’s own body to concentrate their energies upon dealing with the CRF.
Some years ago a Dr. James MacLeod of Cornell University set about the task of creating an rhEPO which would be accepted by an animal’s immune system; and by 1997 tests of a canine EPO had begun. Two years later testing of a feline EPO was started, followed by a one year trial on CRF patients ending in November 2002. It took a further two years for the results to be published, and whilst the trials appear to have gone well, it was found that certain of the cats treated with the feline EPO still developed an antibody to the drug.
RfEPO has not, in any event, been made available to the market; so vets must continue to consider the use of the human version of the synthetic EPO if they are to remove the life threatening symptoms of serious non regenerative anaemia from our CRF feline friends.
December 2009