Hemolytic anemia is a rapidly life-threatening condition. Many of the causes of red blood cell destruction progress quickly. After oxygen is inhaled into the lungs during breathing, it is transferred from the air to the red blood cells. These red cells then carry the oxygen through out the body to all the tissues. Because red blood cells carry oxygen to the tissues, when red cells are depleted the body is basically starved for oxygen.
In addition to oxygen starvation, the destruction of the red cells (hemolysis) releases products from inside of the cells. In large quantities, these products cause some of the signs associated with hemolytic anemia, like jaundiced gums and eyes and discolored urine, which can cause damage to the pet.
There are many causes of anemia other than hemolytic anemia. For instance, an animal may become anemic due to bleeding, or may become anemic when the body makes insufficient quantities of new red blood cells.
Appropriate treatment depends on an accurate diagnosis as to cause. The success rate for the treatment of hemolytic anemia depends on the cause. Some types respond very well to treatment, while others respond poorly even with appropriate treatment.Causes
As mentioned, there are many causes of anemia. The veterinarian's first task after identifying anemia is to determine if the cause is blood loss, insufficient production of blood cells, or hemolysis. Hemolytic anemia refers specifically to those causes of anemia which are due to destruction of the red blood cells. Bleeding is a common cause of anemia, which is not related to hemolysis. For instance, an animal that has bleeding stomach ulcers may be anemic, but it is not hemolytic anemia.
Another type of anemia is due to insufficient production of red blood cells. Red blood cells are made in the bone marrow, or the soft red center of the bones. Decreased production of red cells may be caused by either disease inside the marrow such as cancer in the marrow, or by disease outside the marrow. For example, animals in kidney failure don't send normal signals to the marrow that it should make more red cells.
The most common cause is a disease known as immune mediated hemolytic anemia (IMHA). In this disease, the body's immune system, which is designed to kill germs, instead begins to kill the animal's own red blood cells. This disease occurs far more commonly in dogs than cats. It typically affects young to middle aged animals, with females affected more often than males. Certain dog breeds, including cocker spaniels, poodles, and Old English sheepdogs, are affected more often than other breeds.
Some types of germs and parasites infect the red blood cells directly. These infections can result in destruction of the red cells. Some of these affect dogs more often than cats (Babesiosis), while others are far more likely to affect cats than dogs (for instance, Haemobartonellosis).
Certain toxins can also cause destruction of red cells. These include drugs (like Tylenol, especially in cats), foods (like onions), and metals (like zinc, which is found in a surprising number of common items, including pennies and diaper rash ointments). When a very young puppy develops hemolytic anemia, it is more likely to be due to the ingestion of a toxin than to an immune mediated cause. Recently, there have been reported cases of anemia caused by skunk spray. The alkyl mercaptans and disulfides in skunk spray can cause oxidative damage to the red cells causing heinz-body hemolytic anemia in some dogs.
Mechanical damage to the red blood cells can also result in their destruction. This can occur as a result of the cells being passed through twisted or damaged blood vessels. Examples include a severe and unusual form of heartworm infection, or a twisted spleen (splenic torsion).
There are hereditary diseases in which the red blood cells do not work normally, and these conditions may lead to premature destruction of the abnormal red blood cells. These diseases are most often identified in purebred dogs, and the signs are usually not seen until the animals are young adults.