Lethargic dog
It’s important to understand that anemia itself is not a disease — it is a sign of an underlying problem. So when your veterinarian says, “Your pet is anemic,” he or she is likely going to be looking for the exact reason why. The interesting thing about anemia is that it can occur through a variety of mechanisms, all of which result in an inadequate number of red blood cells in circulation in your pet’s bloodstream. If your pet is producing enough red blood cells to meet normal demand, then everything is working well and there is no problem — your pet’s organs and tissues will receive the proper amount of oxygen, and carbon dioxide (a waste product) will be removed. These are the functions of a healthy red blood cell. However, let supply fall or demand increase and you have a red blood cell crisis on your hands. This article will attempt to explain some of the various reasons why this can occur.

The Red Blood Cell Supply Chain

In order to understand anemia, it may help to think of red blood cell production in terms of a manufacturing process. Bone marrow is essentially the manufacturing plant for red blood cells. The “order” to produce more red blood cells comes from a hormone secreted in the kidneys — erythropoietin. When the body’s supply of red blood cells drops and the kidneys sense a decrease in oxygen, they meet the demand for more red blood cells by producing erythropoietin. This in turn tells the bone marrow to ramp up red blood cell production. But in order for the bone marrow to manufacture red blood cells, certain raw materials, including vitamins and minerals like B12, copper and iron, are required. When the supply chain of these materials falters for some reason, anemia can result.

Indicators of Anemia

When a pet becomes severely anemic, all body systems can grind to a halt due to inadequate oxygen delivery. Without adequate oxygen delivery, your pet may be weak, tired and uninterested in his usual activities. You might notice his normally pink tongue or button nose is pale. Because anemia generally occurs as a result of another disease, you may also see signs of the underlying problem — for example, excessive drinking and urinating in a cat with kidney disease or vomiting in a dog made anemic by the ingestion of onions or garlic.

Let’s take a brief but closer look at some of the many ways the red blood cell process can break down and result in anemia.

1. Insufficient Raw Materials

As we discussed above, without the raw materials, or building blocks, of red blood cells, the bone marrow cannot replace them. Iron deficiency anemia is the classic example of a supply chain failure. Although this type of anemia is common in humans, the typical, commercially available pet diet is replete with iron and the diagnosis of iron deficiency anemia is relatively uncommon in pets but does occur. Cobalamin, or vitamin B12, is another essential ingredient for red blood cell production. In dogs, a congenital disorder in Giant Schnauzers, Beagles, Border Collies and Australian Shepherds can lead to B12 deficiency and result in stunted growth and anemia, which can be reversed by B12 injections. These are two examples of anemia caused by insufficient raw materials.

2. Bone Marrow Failure

The bone marrow is one of the few organs in the body with the capacity to self-renew, even in adults. The marrow contains red blood cell stem cells. Stem cells, throughout an individual’s lifetime, retain the ability to divide and produce replacement red blood cells. Damage to the stem cells from drugs like chemotherapy agents or a decrease in the kidney’s ability to produce the red blood cell stimulating hormone, erythropoietin, can shut down manufacture of red blood cells in the bone marrow. Occasionally, the bone marrow itself develops a disease in which the stem cells stop producing adequate red blood cells, causing anemia. When bone marrow shuts down, we call that disease “aplastic anemia.” These are examples of anemia caused by inadequate production of red blood cells.

3. Hemolysis: Demand Exceeds Supply

Red blood cells have a thin outer shell, or membrane. The membrane allows oxygen into the cell where it binds to hemoglobin, which is the molecule responsible for depositing the oxygen in the blood where it needs to be in our bodies. Although sturdy enough to bend and fold as the red blood cell circulates through the blood vessels, this membrane is easily damaged by drugs or an immune system problem. When damage occurs, the red blood cells can explode. This is called hemolysis. If the red blood cell membrane damage and hemolysis continues unchecked, the bone marrow will not be able to produce enough red blood cells to meet demand. There are a number of things that can cause hemolysis in pets. Infection of red blood cells with such organisms as Babesia, Ehrlichia and Mycoplasma; ingestion of such items as pennies, onions, and garlic; and a disease known as immune mediated hemolytic anemia (IMHA) are well known causes of increased blood cell destruction in dogs and cats.

4. Hemorrhage: Product Diversion

Even if the bone marrow is producing an adequate number of red blood cells and they are not damaged in any way, anemia can result if the red blood cells are diverted from the bloodstream by hemorrhage. From the standpoint of a veterinarian, anemia from blood loss can be extremely difficult to sleuth out. A dog or cat hit by a car and bleeding from an exterior wound is an easy anemia diagnosis, but low-grade blood loss from a bleeding tumor of the intestine, kidney, spleen or nose is much more difficult to detect. Your pet may need to undergo a lengthy series of tests to get to the root cause of anemia.

If Your Pet is Anemic…

Given the complexity of red blood cell production, it is easy to understand why any glitch in red blood cell status makes anemia a common problem in both dogs and cats. Making a diagnosis as to the type of anemia and its cause is critical to determining the appropriate treatment. Figuring out if the cause is due to a “manufacturing” problem (bone marrow failure), destruction of red blood cells (hemolysis) or an inability to keep up with an increased demand due to blood loss (hemorrhage) takes perseverance on the part of the veterinarian and patience on the part of the pet family, but with these two critical elements, anemia can often be corrected.

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