Anemia Due to Enlarged Blood Cells in Dogs

Anemia can sometimes develop due to a deficiency in specific nutrients. Folate is a type of B vitamin while another nutrient, cobalamin, affects its metabolism. These two nutrients control enzymes which code for DNA synthesis in blood cells. Deficiency or poor absorption creates abnormal blood cell precursors in the bone marrow. These cells are called megaloblasts because of their enlarged nuclei. Many megaloblasts die in the bone marrow while others may develop into enlarged blood cells called macrocytes. Megaloblastosis in the bone marrow eventually develops into a condition of anemia that is called megaloblastic anemia. In humans, DNA synthesizing enzymes are produced in the stomach and the condition is often due to a diet inadequate in B vitamins. In dogs, the process is somewhat different. DNA synthesizing enzymes originate in the pancreas rather than the stomach, and dog diets rarely suffer from B vitamin deficiencies. In dogs, megaloblastic anemia is usually the result of a condition which prevents the absorption of folate or cobalamin. This is most commonly the result of a genetic abnormality or another medication. This is a rare type of anemia in dogs.

Problems in DNA synthesis can lead to enlarged, improperly developed blood cells that contribute to anemia. Veterinarians call this megaloblastic anemia because of the presence of megaloblasts in the bone marrow. It is a rare type of non-regenerative anemia in dogs.

Mild forms of anemia are usually non-symptomatic. If your dog has severe megaloblastic anemia, however, you may see the traditional symptoms of anemia. These should be evaluated by a veterinarian.

• Poor appetite
• Weight loss
• Lethargy
• Lack of stamina
• Weakness
• Rapid heart rate (tachycardia)
• Rapid breathing (tachypnea)
• Paleness of mucus membranes, especially notable around the gums
• Blood in the stool

Types

There are two basic types of anemia.

Regenerative anemia – this is a type of anemia in which the bone marrow is not affected and will therefore react to the condition with a strong production of new blood cells

Non-regenerative anemia – since megaloblastic anemia originates from bone marrow problem which affects blood cell production, it is considered non-regenerative

These two conditions could also be relevant to your dog’s diagnosis.

Megaloblastosis

• This is a condition in which the bone marrow is full of megaloblasts or poorly developed blood cell precursors
• It leads to megaloblastic anemia

Macrocytosis

• As a diagnosis this indicates some degree of enlargement in the blood cells
• It may be present without anemia (this is an inherited condition in poodles)
• In humans, high levels of macrocytes generally indicate megaloblastosis in the bone marrow, but this correlation isn’t as remarked in dogs
• Most veterinarians use some degree of macrocytosis as a preliminary indication of regenerative anemia since strong bone marrow stimulation can also create immature, enlarged blood cells
• Other factors, like white blood cell and platelet counts, would also be relevant to the veterinarian’s interpretation of macrocytosis

These are the most common causes of megaloblastic anemia in dogs.

Inherited inability to absorb cobalamin

• More common in some breeds
• Giant Schnauzers
• Border Collies
• Beagles
• Australian Shepherds

Chemotherapy drugs

• which inhibit folate absorption

Other drugs

• Methotrexate (cancer medication)
• Hydroxurea
• Trimethoprim-sulpha
• Fenbendazole
• Quinidine
• Some anti-convulsion medication

Overgrowth of intestinal bacteria

• In dogs this only leads to anemia in prolonged cases

Nutritional deficiency (folate or cobalamin)

• This isn’t common in dogs, although it has been created in laboratory situations

Your dog’s veterinarian will be able to diagnose anemia with a blood cell count. A blood smear test will indicate the presence of macrocytes, or enlarged blood cells. By itself, this won’t absolutely indicate megaloblastic anemia, but low counts of white blood and platelet cells may help to suggest a non-regenerative bone marrow problem. A bone marrow biopsy or aspirate might be necessary to make an accurate diagnosis. These tests involve inserting a hollow needle into the bone marrow to obtain a sample that can be analyzed microscopically. Sedation or total anesthesia would be necessary. The veterinarian will need your dog’s complete medical history, as well as any medications he is taking. Family history and breed could also be relevant since hereditary factors play a part. The exact nature and onset of symptoms will also be helpful.

Most problems can be rebalanced with a supplement of folate or cobalamin depending on the condition. Dogs with a hereditary inability to absorb cobalamin many need to continue supplements intermittently for the remainder of their lives. Dogs with megaloblastic anemia as a side-effect to another drug may also need to take supplements to start with. If the other drug can be discontinued or reduced, the system will likely rebalance itself. This could be more difficult with conditions like cancer, and continual supplements might still be necessary. Poodles diagnosed with macrocytosis or megaloblastosis, but no corresponding anemia, don’t need to be treated.

Dogs with an inherited tendency to megaloblastic anemia will probably need to take supplements throughout their lives. Since this is a nutritional supplement, it shouldn’t cause other negative side effects, but your dog may need regular check-ups and tests to adjust dosage. In other cases, dogs will likely make a complete recovery, unless the condition occurs as a response, or in combination with, another life threatening condition. Regular blood tests to check for anemia are advisable, if your dog does recover.