totw: Diagnosing Immune Disease
General Diagnostics to Run
When your veterinarian suspects an immune mediated disease it is important to screen for any underlying diseases that can stimulate the immune system. Common diseases that can trigger an auto-immune response is cancer, and tick borne diseases.
Cancer screening include thoracic radiographs (chest x-rays), abdominal ultrasound, and full blood work including a chemistry and CBC.
Tick borne disease testing looks for these common infections that can trigger an immune response:
Disease Specific Diagnostic Tests
For immune mediated blood disorders a bone marrow biopsy, cytology, and/or culture may be indicated to look for cancer, infection, or primary bone marrow dysfunction.
A test specific to immune mediated hemolytic anemia (IMHA) is a Coombs test which looks for specific red blood cell antibodies which can differentiate traditional anemia from immune mediated anemia. Basic microscopic exam of a blood smear can also diagnose IMHA with the presence of spherocytes.
Unfortunately, immune mediated thrombocytopenia (IMTP) is usually a diagnosis of exclusion, meaning everything else is ruled out before it can be deemed the primary diagnosis. There is a platelet surface-associated immunoglobulin test, but is has been shown to not be able to differentiate between primary or secondary IMTP. The other big issue is that there are a lot of false-positives. Because of these issues, many veterinarians do not run these tests to diagnose IMTP.
Immune mediated neutropenia (IMN) can be difficult to diagnose. Low numbers of neutrophils are noted even when a patient is not suffering from an infection. It is essential to rule out any other cause of low neutrophils which usually include severe infection. Patients are usually on antibiotics for the secondary infections. Immunosuppresents are started when IMN is suspected to see if the body stops destroying the neutrophils so important in preventing infections.
Other Immune Mediated Diseases
For immune mediated polyarthritis a joint tap is indicated to obtain cytology and cultures. The cytology looks for inflammatory or infectious agents.
Other immune diseases may require a biopsy of the tissue effected.
We hope this helps you understand the different tests that may be run for your pet when your veterinarian suspects an autoimmune disease. We'll dive deeper into each disease in future posts. Check the either the hematology page or the immunology page for specific diseases.
Yvonne Brandenburg, RVT, VTS (SAIM) is a Registered Veterinary Technician practicing in California and obtained her Veterinary Technician Specialty in Small Animal Internal Medicine in 2016. She is the founder of InternalMedicineForPetParents.com. For more about Yvonne visit her author page here.
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