Anemia means a decreased number of red blood cells in circulation. Packed Cell Volume (PCV, also often called hematocrit) is the most common way to measure anemia and refers to the percentage of blood volume that is taken up by red blood cells. The normal PCV for a cat is 25-45%, and any PCV below 25% is considered anemic. 

Red blood cells carry oxygen and nutrients to the body’s tissues. These cells circulate for about 70-80 days before being removed from circulation and replaced with new red blood cells from the bone marrow. Without enough red blood cells in circulation, cells will not receive enough oxygen or nutrients to survive, so anemia can become a critical or even fatal situation very quickly.

Clinical Signs

Because anemia starves the body of oxygen (the body’s fuel), the first sign is often lethargy. An anemic cat may have little energy to play or may sleep more than usual. The cat’s gums may appear almost white or even yellow (a condition called jaundice) due to red blood cell destruction. In extreme cases, the cat may have trouble breathing, and respiratory and heart rates can increase as the body tries to compensate for the lowered oxygen delivery by the red blood cells.

Depending on the cause of anemia, fever and loss of appetite may occur due to an infection or inflammatory response. Black stools can be seen if blood loss occurs in the stomach or intestinal tract, and discolored urine can be a sign of red blood cell destruction. The signs of anemia can be very vague, however, and if a cat has been anemic for a long time, their body has likely had time to compensate and the cat may show no signs at home.

Causes of Anemia

There are many causes of anemia in the cat, but they can be broken down into three major categories: loss of red blood cells, destruction of red blood cells, and failure to produce new red blood cells. A discussion of some, but not all of the common causes of anemia from each of those categories is provided below.  Feline anemia is common and can be secondary to many health conditions.

Loss of red blood cells

Loss of red blood cells (hemorrhage) can be due to an obvious source such as a wound or trauma, or from more insidious causes. Flea and tick infestations are a major cause of anemia, especially in kittens, as the parasites suck blood from the body faster than it can be replaced.  The hookworm parasite (Ancylostoma tubaeforme), which feeds on blood in the intestines, can cause anemia in cases of severe infestation. 

Hemorrhage can also occur in the stomach or intestines due to ulcers or inflammation in the gastrointestinal tract. Cats with blood loss in these areas may have chronic vomiting, diarrhea, or black stools.

Reticulocytes are a specific type of red blood cell made and released by the bone marrow when it senses anemia in an attempt to compensate for the low red blood cell numbers. With chronic blood loss through the intestinal tract or from parasites, cats would be expected to show an elevated reticulocyte count. When a cat has a low red blood cell count and high reticulocyte count, this is called a “regenerative” anemia, as the body is reacting appropriately to blood loss. As long as red blood cells are being lost faster than reticulocytes can be released from the bone marrow, however, the cat will remain anemic.

Destruction of red blood cells

Red blood cells that have reached the end of their lifespan (about 70-80 days) are routinely removed from circulation by a cat’s body and replaced by new red blood cells made in the bone marrow. However, certain diseases can cause red blood cells to be broken down or destroyed more quickly than normal, leading to anemia as they are removed more quickly than they can be replaced.

Certain infectious diseases can lead to damage and destruction of red blood cells. These include Mycoplasma haemofelis, Candidatus, Mycoplasma haemominutum, Cytauxzoon felis, and Babesia species infections. These diseases are spread to cats by fleas and ticks, and they then attach to red blood cells, leading to their destruction.

Red blood cells can also be damaged by certain toxins. Oxidative injury to red blood cells secondary to the ingestion of acetaminophen (Tylenol ®), zinc, copper, onions, and some other toxins or medications can lead to anemia in cats.

Occasionally, a cat’s body tags its own red blood cells as foreign, causing them to be destroyed by the cat’s own immune system. This is called Immune-mediated hemolytic anemia (often abbreviated to IMHA). In some cases, there is a trigger causing the immune system to incorrectly destroy too many red blood cells. This trigger can include a reaction to a drug, cancer, or infectious diseases such as Feline Leukemia Virus (FeLV) or feline infectious peritonitis (FIP). If there no underlying cause for the inappropriate activation of the immune system is identified, this disease is called primary IMHA. There is no evidence that this is a hereditary disease in cats.

Anemias caused by loss or destruction of red blood cells are typically regenerative, so an elevated reticulocyte count would be expected as the body tries to compensate for the destruction of red blood cells.

Failure to produce red blood cells

New red blood cells are produced in the bone marrow to replace those that are regularly removed from circulation. A hormone produced in the kidney, called erythropoietin, is the primary signal that tells the bone marrow that more red blood cells are needed in the body. If the bone marrow is not able to produce enough red blood cells to replace those that normally outlive their lifespan, a cat will develop a non-regenerative anemia, with a low reticulocyte count.

One common cause of non-regenerative anemia in cats is chronic kidney disease. Chronic kidney disease is a very common, affecting approximately 15-30% of geriatric cats. When the cells in the kidney degenerate, they release less erythropoietin, leading to lowered red blood cell production by the bone marrow. As chronic kidney disease advances, 30-65% of affected cats will develop some degree of anemia.

Problems within the bone marrow itself can also lead to decreased production of red blood cells. Cancer, immune-mediated disease, or inflammation in the bone marrow can reduce its ability to replace red blood cells. Chronic inflammation elsewhere in the body can also impair the ability of the bone marrow to effectively produce red blood cells. This is often referred to as “anemia of chronic disease”, and can be seen with many other illnesses in cats, including FeLV infections and various cancers.

Diagnosis

The first step in diagnosing anemia is to determine the packed cell volume, or PCV. This test involves spinning down a small blood sample in a centrifuge to determine what percentage of the overall blood volume is made up of red blood cells. Further blood testing can look for evidence of regeneration in the red blood cells, abnormalities in other blood cell types such as white blood cells and platelets, evidence of organ damage such as chronic kidney disease, or the presence of infectious diseases.

Other tests, such as radiographs (x-rays) or an ultrasound to look for causes of bleeding or a bone marrow biopsy, may be recommended by a veterinarian,

Treatment

Treatment for anemia will vary depending on the underlying cause. In some cases, treatment for parasites or infectious diseases will be most important to stop the loss or destruction of red blood cells. Medications can be used to help stop bleeding from the gastrointestinal tract, and steroids and other immune-modulating drugs are essential in the treatment of immune-mediated diseases.

In cases of severe anemia, a blood transfusion may be necessary to replace red blood cells that have been lost or destroyed while the underlying condition is being treated. Cats have two major blood types, so it is important that both the donor and recipient blood be tested to reduce the risk of any reactions to the blood transfusion. 

In the case of chronic kidney disease, a medication called darbepoetin is available to help stimulate the production of new red blood cells in the bone marrow by replacing erythropoietin normally made in the kidneys. This medication requires weekly injections and close monitoring for side effects, but can result in resolution of anemia in 60-65% of cats with chronic kidney disease.

Last updated 2021