Improving the Diagnosis of Immune Thrombocytopenia in Dogs

Platelets are small cells found in the blood that bind together and plug holes in damaged blood vessels. These plugs seal the damaged vessel until a more permanent and structurally sound repair can be made. But what if there aren’t enough platelets to do the job? Abnormal bleeding would occur as everyday scrapes and bumps occur, and catastrophic bleeding could happen if a large wound or surgical incision were created.

This is unfortunately what happens in the disease called immune thrombocytopenia (ITP). The immune system malfunctions and destroys platelets, leading to dangerous bleeding. In dogs, ITP is most common in middle-aged females. Any breed can be affected, but the disease is most common in mixed breeds, Cocker Spaniels, Poodles, and Old English Sheepdogs. Clinical signs of ITP include spontaneous bruising, bleeding, decreased energy, decreased appetite, pale gums, fever, rapid breathing, and anemia. 70-90% of dogs will recover, but relapses are common and up to 30% of affected dogs will not survive. Treatment involves the long-term use of drugs that suppress the immune system.

Laboratory test results and clinical findings can help differentiate primary from secondary immune thrombocytopenia cases.

Anything that normally triggers the immune system can trigger ITP. This includes cancer, bacterial or viral infections, drugs, or toxins. These cases are called secondary ITP – indicating that the immune system malfunction is secondary to a known trigger. In some cases, the underlying cause cannot be identified. This is called primary ITP and, by definition, indicates that all known triggers have been ruled out.

The clinical course of primary ITP varies greatly. Some dogs will respond readily to immunosuppressive drugs, while others require blood transfusions and succumb to severe bleeding. It is difficult for veterinarians to distinguish primary from secondary ITP or predict how a case will respond to treatment. To fill this knowledge gap, the Old English Sheepdog Club of America and English Cocker Spaniel Club of America Health and Rescue Organization worked with the AKC Canine Health Foundation (CHF) to fund research exploring ways to differentiate primary from secondary ITP, and how to identify the most severe cases (CHF Grant 02536-MOU: Immunoprofiling to Combat Canine Immune Thrombocytopenia).

Researchers examined data on dogs representing 50 different breeds and mixed breeds seen at multiple veterinary clinics in the Northeastern United States. They compared these cases' clinical findings and laboratory test results to see if any single test or group of tests could clearly diagnose dogs with primary ITP and if dogs with severe disease had any defining features or test results. They found that:

• Dogs with primary ITP had lower concentrations of several blood markers (platelet count, platelet membrane protein expression, and D dimer). However, these low levels were also seen in some dogs with secondary ITP, meaning veterinarians must still use their clinical judgment to differentiate these two disease forms.  

• Combining the above test results with a dog’s sex and blood clotting test results (coagulation profile) improved the accuracy of identifying primary ITP cases.

• Dogs that presented with a low red blood cell count (hematocrit) and elevated BUN (blood urea nitrogen) were less likely to survive.

This study arms veterinarians with valuable information to rapidly identify dogs with primary ITP and predict which dogs have more severe disease. For owners, this means a more accurate prognosis for their dog and helps guide treatment decisions. Aggressive therapies can be started earlier for dogs with severe disease, while the side effects of long-term immunosuppressive therapy can be limited in dogs with milder disease.

Thanks to the collaborative efforts and support of organizations like the Old English Sheepdog Club of America and the English Cocker Spaniel Club of America Health and Rescue Organization, CHF continues its mission to find and fund research studies that help prevent, treat and cure canine disease. Working together, we can make a brighter future for our beloved dogs. Learn more about this important work at akcchf.org/research.