Anemia can be a primary problem, which significantly affects your pet's well being, or it can be secondary to other disease processes, in which case it might or might not cause important clinical illness. The most common causes of severe anemia in cats include blood loss and red blood cell destruction. External blood loss is generally caused by trauma. Significant internal blood loss in cats most often occurs due to either bleeding into the intestinal tract or bleeding into the abdominal cavity. Respiratory tract disease. Diseases of the lungs and/or airways may cause an increased respiratory rate and possible collapse, if severe.
Vehicular trauma is a common cause of bleeding into the abdomen. This results from damage to the liver and/or spleen and sometimes the kidneys. This type of blood loss cannot be seen, but can be life threatening and will often result in collapse. Tumors associated with the liver and spleen can also cause significant bleeding into the abdomen. A third common cause of bleeding into the abdomen is rat poison ingestion, which inhibits normal blood clotting.
Bleeding into the intestinal tract will often result in the formation of black, tarry stools. This can be secondary to cancer, severely low platelet counts (platelets are the blood cells that aid in blood clotting), or severe inflammatory disorders of the gut.
Red blood cell destruction commonly occurs in cats due to an immune-mediated disease in which the body destroys its own red blood cells. This type of anemia is called hemolytic anemia. Hemolysis may also be caused by cancer, exposure to certain drugs, vaccine reactions, heavy metal toxicity (zinc, copper), and infectious diseases, several tick-borne diseases in particular.
Any chronic illness can cause anemia. This type of anemia is usually mild to moderate, and does not significantly impact the pet in most cases.
As discussed, there are many causes of anemia and therefore many different clinical signs. Other diseases that may cause signs of generalized weakness, collapse and increased respiratory rate include:
Cardiovascular disease. Heart abnormalities may result in collapsing or fainting episodes, which may look similar to an animal that collapses due to severe anemia. Additionally, heart disease can cause secondary lung problems, which may result in an elevated respiratory rate. Heart disease may also cause poor circulation, which can result in pale gums, making the animal appear anemic.
Seizures or other neurologic disease. Episodes of collapse may be difficult to differentiate from a seizure.