|What is anemia? Causes of anemia Symptoms of anemia Role and composition of the red blood cells Diagnosing the cause of anemia Treating anemia|
Anemia is a condition characterised by a reduced number of red blood (also known as erythrocytes) cells in the blood. Is not a disease in itself but a symptom of an underlying condition. It may be caused by blood loss, red blood cell destruction (known as hemolysis) or inadequate red blood cell production.
There are two forms of anemia, regenerative and non-regenerative.
- Regenerative anemia - This is the most common type of anemia in cats. The bone marrow is able to produce red blood cells but this may not occur quickly enough to replace red blood cells which are lost. Regenerative anemia can be further broken down into diseases which cause blood loss (such as trauma or certain parasites) and diseases which cause red blood cell destruction (hemolytic anemia).
- Non-regenerative anemia - Inadequate red blood cell production is classified as non-regenerative anemia. This is where the body is unable to produce enough red blood cells in the bone marrow.
Role and composition of red blood cells:
Blood is composed of three different types of cells which is suspended in plasma, the liquid component of blood. All blood cells are made in the bone marrow, the spongy internal core of the bones. Bone marrow makes stem cells, which develop into one of the three types of cell within the blood. Red blood cells, white blood cells and plasma.
Red blood cells are the most abundant cell within the body and makes up approximately 40% of the blood's volume. The role of red blood cells is to carry oxygen from the lungs to the tissues via the circulatory system (the heart, which pumps the blood and the blood vessels which transport it around the body) and remove carbon dioxide. Red blood cells contain a protein called hemoglobin, which is composed of four globulin chains, within the chain is heme, which contains an iron atom which carries the oxygen in the red blood cells. It is heme which gives blood its red colour.
Red blood cells remain in the circulation for approximately 73 days before they are broken down and recycled by the spleen, liver and bone marrow.
Regenerative anemia (due to blood loss):
- Hemorrhage (blood loss). The danger of sudden blood loss is twofold. Hypovolemic shock is the reduction of blood (more importantly, blood plasma, the fluid component of blood) which makes it harder for the heart to pump blood around the body resulting in multiple organ failure. Hemorrhagic anemia occurs due to the loss of circulating red blood cells.
- Parasites such as worms, fleas which feed on the cat's blood, kittens are particularly vulnerable, as are cats with heavy parasite burdens.
- Certain tumours which can result in bleeding.
- Blood clotting disorders.
- Gastric ulcers - Open sores which develop in the layers of the stomach which expose the delicate tissues to stomach acid resulting in internal bleeding.
- Hemophilia - This bleeding disorder is due to an inability of the blood to clot properly therefore blood loss is greater than is normal. Hemophilia can occur both internally or externally (such as a cut to the skin). Unfortunately it is often difficult to detect internal bleeding. Vomiting blood or dark/tarry stools can be a sign of internal bleeding in cats.
The most common causes of blood loss in young cats is parasites, older cats are more likely to suffer from tumours or gastrointestinal ulcers.
Regenerative anemia (due to red blood cell destruction):
- Blood parasites - Hemobartonella, ehrlichiosis and cytauxzoonosis cause anemia due to destruction of the red blood cells.
- Immune-mediated hemolytic anemia (IMHA), is a disease in which the cat's own immune system can become directed against its own red blood cells.
- Feline leukemia virus and Feline immunodeficiency virus - Both of these feline retroviruses can cause anemia by increased red blood cell destruction as well as decreased red blood cell production (see below).
- Heinz-body hemolytic anemia - Ingestion of certain medications, foods or toxins such as acetaminophen, naphthalene mothballs, propylene glycol, copper, zinc, onion can cause the formation of heinz bodies on the red blood cells which results in their destruction by macrophages (a type of white blood cell).
- Neonatal isoerythrolysis (blood type incompatibility) - This life-threatening condition occurs when a kitten with type A blood nurses from its mother who has type B blood in its first 24 hours of life. Colostrum is made by the mother cat contains naturally occurring antibodies against the kitten's type A blood leading to the red blood cells being destroyed.
Aplastic anemia occurs when the bone marrow fails to produce enough blood cells. There are a number of causes including certain medications such as antifungals, chemotherapy drugs, certain antibiotics, radiation, toxins, bacterial or viral infections.
- Feline leukemia virus and feline immunodeficiency virus - Anemia can develop due to the virus suppressing red blood cell production in the bone marrow as well as producing bone marrow abnormalities such as abnormal maturation or malignant transformation of cell lines.
- Chronic renal disease - As the kidneys become damaged, they don't produce enough erythropoietin (EPO), a hormone which stimulates the bone marrow to produce more red blood cells. Blood loss from ulcers may also play a role in anemia in cats with CRD.
- Nutritional deficiency - If the diet contains inadequate amounts of iron, which is required for red blood cell formation, then anemia can develop, this may also occur due to poor absorption of food.
- Chronic inflammatory disease - Known as anemia of chronic disease (ACD), any long term inflammation, chronic infection and malignancy can ultimately lead to a decrease in red blood cells. This is known as anemia of inflammation. The cause is still not fully understood, but increased numbers of cytokines (molecules secreted by immune system cells which act as chemical messengers) are believed to cause reduced response to EPO (the hormone which stimulates the production of red blood cells), reduced formation of new red blood cells and inhitibs the release of iron from stores.
- Certain cancers such as leukemia which can affect blood cell production in which cancerous cells crowd out healthy stem cells in the marrow.
Symptoms of anemia relate to a deficiency in the amount of oxygen (known as hypoxia) reaching cells within the body.
- Pale mucous membranes - When oxygen levels drop, the body compensates by prioritising blood flow to the vital organs such as the brain and liver. Capilliaries in the skin contract, which makes it harder for the blood to make its way there, therefore shunting the blood flow to the vital organs. This gives the skin and mucous membranes their paler colour.
- Yellow skin and mucus membranes (jaundice) - If the red blood cells are being destroyed (known as hemolysis) too quickly such as immune mediated hemolytic anemia, heinz body hemolytic anemia, neonatal isoerythrolysis or certain parasites which destroy blood cells, bilirubin can build up causing the yellow discoloration.
- Rapid breathing and pulse (tachypnea).
- Tachycardia (increased heart rate) - The heart tries to compensate for reduced oxygen levels in the blood by increasing output which can eventually lead to heart failure.
- Sleeping more than usual.
- Lethargy - Due to reduced oxygen in the tissues.
- Black, tarry stools (melena) can develop if your cat is bleeding internally.
Miscellaneous symptoms of anemia may also include:
Other symptoms may also be present depending on the underlying cause of anemia.
Your veterinarian will perform a complete physical examination of your cat and obtain a medical history from you. Tests he may wish to perform include:
- Complete blood count. A series of tests which evaluates the cellular components of blood (red blood cells, white blood cells and platelets). Elevated numbers of reticulocytes (immature red blood cells) would point to regenerative anemia. Regenerative anemia is indicative of either blood loss or red blood cell destruction. Packed cell volume (PCV) is a measure of the percentage of red blood cells in circulating blood. An anemic cat will have a PCV of < 24%
- Blood smear to check for the presence of blood parasites, reticulocytes and abnormalities of the red blood cells.
- Biochemical profile to evaluate the overall health of the cat and determine if there is any organ involvement.
- Fecal examination if gastrointestinal blood loss is suspected.
- Xray to check for foreign objects, evaluate the organs and look for tumours.
- Bone marrow biopsy for cats with nonregenerative anemia to determine why the bone marrow isn't producing enough red blood cells as well as to check for cancers.
- Coombs test (also known as antiglobulin test or direct antibody test), this test is to detect the presence of antibodies which can bind to the surface of red blood cells.
- FIV and FeLV tests should also be carried out as these two viral infections are a common cause of anemia in cats.
Finding and treating the cause of anemia is the goal. In addition to treating the underlying cause, your cat may require supportive care which may include:
- Volume replacement - Hypovolemic shock is a life threatening condition which occurs when a large portion of the blood is lost. Immediate treatment for this is volume replacement to ensure blood volume to prevent ischemia (restricted blood supply to the tissues, which results in lack of oxygen and glucose), shock and multi-organ failure.
- Blood transfusion may be indicated for acutely anemic cats or cats who have suffered significant blood loss or kittens who have neonatal isoerythrolysis. Blood typing must be carried out before a blood transfusion. Cats have three blood types, Type A, Type B and Type AB. Type A cats can only receive type A blood, Type B cats can only receive type B blood and Type AB cats can receive blood from type AB blood or type A blood.
- Erythropoietin: The kidneys produce a hormone, erythropoietin, which instructs the bone marrow to produce red blood cells. Cats with kidney failure often have a low red blood cell count. Only the human form is available and some cats may eventually recognise this substance as foreign and antibodies will be created against it.
- Oral iron supplementation may be administered to cats with iron deficiency.
- Oxygen therapy may be required for severely anemic cats.
Treading underlying causes:
- Anti-parasitic medication for fleas or worms.
- Antibiotics oxytetracycline or doxycycline and treatment with high doses of immunosuppressive drugs such as prednisolone will be given to diminish the immune-mediated component of the disease process if the cat is found to have feline infectious anemia.
- Surgery and or chemotherapy to treat cancer or remove zinc containing foreign objects.
- Anti-viral medication will be prescribed to cats with FIV or FeLV, supportive care is also necessary.
- Nutrition - Feeding your cat a nutritionally balanced diet.
- Discontinuing medications which cause anemia.
- Stomach acid reducing medications such as cimetidine, ranitidine or famotidin can be given to cats with gastric ulcers as well as Sucralfate, which forms a gel like substance to cover ulcers and prevent further blood loss (and damage).
- Bland diet - This can be given to cats who have gastric ulcers. Foods include poached chicken and rice.
Image courtesy of Wellcome Images.
Last updated 5th February 2017.