Within red blood cells is a protein called hemoglobin, which functions to transport molecular oxygen in the blood to all body tissues. Normally, as red blood cells age or are damaged, they are broken down by other cells, called macrophages. Part of the hemoglobin molecule is recycled to the bone marrow to be incorporated into new erythrocytes. Other parts of old or damaged RBCs are processed and excreted by the liver. When cats have an abnormally low red blood cell mass – and therefore an abnormally low amount of hemoglobin available to carry oxygen molecules – they can experience varying degrees of oxygen starvation. Anemia manifests clinically by weakness, lethargy, exercise intolerance, elevated heart rate, bounding pulses, pale mucous membranes, confusion, appetite loss, rapid breathing and ultimately collapse. Veterinarians are able to diagnose anemia in cats by assessing their red blood cell count (RBC) and packed cell volume (PCV).
There are three general causes or categories of anemia in companion animals: anemia due to blood loss, red blood cell destruction and decreased production of red blood cells. The first two of these are referred to as regenerative anemia; the last is referred to as non-regenerative anemia.
Acute blood loss, such as from trauma, surgery or other acute-onset bleeding disorders, causes anemia because there is a decrease in the overall number of circulating erythrocytes. This form of anemia can also be caused by chronic blood loss, whether from gastrointestinal bleeding due to ulcers, internal parasites, cancer, external parasites/flea or tick infestation or otherwise.
Hemolytic anemia is caused by either destruction or an abnormally short life-span of red blood cells, leading to a reduced overall circulating red blood cell volume. Hemolytic anemia can be immune-mediated or non-immune mediated. Auto-immune hemolytic anemia is a condition in which the cat's body for some reason perceives its own RBCs as being foreign and starts a cascade of immunological processes to destroy those cells. This is uncommon in cats. Non-immune-mediated hemolytic anemia is caused by destruction of RBCs by something other than the cat's own immune system, such as red blood cell parasites, hereditary diseases or toxins.
Non-regenerative anemia is a serious condition which is often a consequence of underlying disease. Some conditions that can cause non-regenerative anemia in cats include bone marrow neoplasia, renal disease and feline leukemia. In these cases, the anemia cannot be resolved unless the underlying condition can be resolved.
Whether the anemia is regenerative or non-regenerative will help a veterinarian determine the best way to treat the condition.
Preventing Anemia in Cats
There is no effective way to prevent cats from becoming anemic. Feeding a high-quality diet, preventing traumatic injuries, keeping current on vaccinations and following sound anti-parasitic protocols will all help reduce the occurrence of anemia in cats.