Low White Blood Cell Count in Dogs

As part of the body’s immune system, white blood cells provide defense against disease. A drop in the total number of circulating white blood cells, called leukopenia, puts the dog at a higher risk of infection. As well as the overall count, blood tests will measure the number of each particular type of cell. Neutrophils are the most numerous white blood cell in dogs. They are the first cells to respond to an infection, travelling quickly to the site and binding to the foreign bacteria or virus that is causing the problem. Neutrophils are short-lived cells, generated in large numbers by the bone marrow. A low number of neutrophils, called neutropenia, is the most common reason for leukopenia in dogs. Many acute or long-lasting infections can cause neutrophil numbers to drop because the cells are destroyed faster than the bone marrow is able to compensate. Autoimmune responses, genetic disorders found in some breeds, cancer, and drug toxicity can also cause neutropenia. With disorders that affect the bone marrow, the condition may be combined with low levels or red blood cells and platelets as well, since the stem cells in the bone marrow may be unable to generate any type of blood cell. While leukopenia is not a definitive diagnosis, analyzing the numbers and different types of blood cells that are present will help the veterinarian identify your dog’s disease.

A drop in the total number of circulating white blood cells, called leukopenia, makes a dog more susceptible to any type of infection. Neutropenia, low numbers of the white blood cells called neutrophils, is the most common type of leukopenia in dogs. This disorder is usually the result of an underlying cause, such as infection, cancer, or a genetic abnormality.

The most common sign of a low white blood cell count in dogs is an inability to fight off infections. Take your dog to the veterinarian if you notice signs of persistent or recurring infection.

• Fever
• Vomiting
• Diarrhea
• Lethargy
• Bleeding
• Pale coat and nose

Depending on the primary cause, neutropenia could be present with many different types of symptoms.

Types

Blood test results can often show reduced numbers among different types of white blood cells.

• Leukopenia – drop in the total number of white blood cells, usually due to neutropenia
• Neutropenia – low numbers of neutrophils associated with infection, autoimmune response and genetic disorders
• Pancytopenia – an extreme form of neutropenia with a simultaneous reduction in red blood cells and platelets; often associated with bone marrow dysfunction or failure
• Lymphopenia – low numbers of lymphocytes often associated with a stress response that causes high levels of cortisol; doesn’t usually cause leukopenia unless neutropenia is also present
• Eosinopenia – a low levels of eosinophils; also indicates a stress response

Many disorders can cause white blood cell numbers to drop in dogs.

Prolonged or overwhelming infection

• Canine Parvovirus
• Infectious hepatitis
• Coronavirus

Cancers of the bone marrow

Sepsis

Drugs

• Chemotherapy drugs
• Some antibiotics (trimethoprim sulfamethoxazole)
• Dipyrone (fever medication)
• Estrogen replacement therapy

Autoimmune diseases

Ehrlichia (infection by a tick-borne parasite)

Genetic disorders

• Grey collies (cyclic hematopoiesis or canine cyclic neutropenia)
• Giant Schnauzers (malabsorption of vitamin B)

White blood cell counts in dogs are measured using a leukogram. In most cases, this will be part of a complete blood cell count (CBC) that also measures red blood cells and platelets. Some abnormal leukogram results include leukopenia and neutropenia. 

An Inflammatory Response or 'left shift' means there are high numbers of immature neutrophils caused by increased bone marrow production. If this corresponds with neutropenia, it is called a degenerative left shift. It suggests either a very recent infection, or a severe systemic disease that is destroying neutrophils faster than bone marrow generation. Your dog’s other symptoms and the degree of neutropenia may further help to indicate the cause. Very low neutrophil numbers are usually associated with canine parvovirus, while other infections will only have mildly depleted levels. Few or mild symptoms of infection could indicate an autoimmune disorder that is destroying neutrophils in the blood.

Neutropenia can occur cyclically, as with the genetic disease of gray collies. This diagnosis will depend on your dog’s breed and age, since most collies with this condition do not survive past 2 years of age. Neutrophil numbers drop in approximately 12 day cycles.

If there are few immature cells present, this could indicate a problem with the bone marrow, such as cancer, an auto-immune disorder that affects neutrophil stem cells, or drug toxicity. Pancytopenia, a decrease involving all types of blood cells, will usually develop as the disease progresses, so this may show up on a CBC. Ehrlichia, a parasite infection passed through ticks, can present similar symptoms so the veterinarian will test for this as well.

Other information about your dog can help the veterinarian make an accurate diagnosis, including their age and breed, as well as past and present medications and any toxin exposure. Vaccinations and potential exposure to infection are also relevant. The veterinarian will perform a full physical examination and take urine and possibly fecal samples to thoroughly evaluate your dog’s health.

Treatment will depend on the cause of neutropenia. Dogs with bacterial infections will be given antibiotics. This will help to support the immune system which is weakened with any type of leukopenia, whether bacterial infection is the primary cause or not. Fluids, electrolytes, and other supportive treatment may be necessary for dogs with very severe infections.

Dogs with immune-mediated neutropenia will respond to immune suppressants, so prednisone or another steroid may be given if the veterinarian does not believe that infection is the primary cause. Immune suppressants should not be given to dogs with severe infections as this will limit the body’s natural disease fighting response.

Cancerous conditions will be treated with chemotherapy. Unfortunately, this treatment will often further deplete your dog’s white blood cell count. Antibiotics will likely be given at the same time to support your dog’s immune system.

Gray Collies with inherited neutropenia will rarely survive into adulthood as there is no treatment except to manage bacterial infection as much as possible. A bone marrow transplant could cure the condition, but this is a costly and risky procedure that is rarely done in dogs.

If the problem is due to another drug, the veterinarian will try to eliminate this drug or reduce the dosage.

Leukopenia can be the sign of many serious conditions that require lifelong management. Blood cancers may respond to chemotherapy, but the prognosis is guarded. Many other potential causes could require long-term medication and your dog will need to be monitored carefully for side effects or toxicity. If infection is the primary cause, your dog may make a full recovery, as long as he survives the initial disease. The prognosis will depend on the diagnosis of a veterinarian.

Leukopenia can be expensive to treat. To avoid high vet care expenses, secure pet health insurance today. The sooner you insure your pet, the more protection you’ll have from unexpected vet costs.