Flashcards in Hematology - IMHA Deck (64)
What is the pathogenesis of IMHA?
The immune system produces antibodies that bind to the patient's own RBCs leading to RBC destruction via intravascular and extravascular hemolysis
What is the most common form of IMHA (think antibody)?
IgG mediated - where RBCs are destroyed by macrophages in the liver in the spleen (Extravascular)
How do spheryocytes form?
When macrophages consume a piece of the RBC membrane and not the entire thing they leave fragments called spherocytes
IgM activates complement better than ____ which leads to ______ destruction ultimately resulting in ______ hemolysis.
IgG; intravascular; intravascular
What are the three etiologies of icterus?
Pre-hepatic due to hemolysis, hepatic, and post-hepatic due to biliary obstruction
How do you differentiate between the etiologies of icterus?
Obtain minimum database of CBC, chemistry panel, and urinalysis
Why may a dog with IMHA have a non-regenetative anemia at presentation when it is more commonly associated with regenerative anemia?
Immune attack at the level of the bone marrow OR early disease
What test is commonly positive in patients with IMHA?
Saline agglutination test
What is agglutination in IMHA patients induced by?
five-armed IgM or large quantities of IgG
How do you perform a slide agglutination test?
Mix 4 drops of saline with 1 drop of anticoagulated whole blood on a slide. Gently agitate and then examine for macroagglutination. Look under microscope for microagglutination
When evaluating a slide agglutination test, what must you look for that is not agglutination due to IMHA?
When should a Coomb's test be performed?
Only if there is negative autoagglutination
In an IMHA patient, why would there not be autoagglutination?
The anti-RBC antibody levels are too low to cause agglutination
What does the Coomb's test detect?
antibodies or complement attached to RBCs
What is a common CBC finding in patients with IMHA?
Very high WBC counts
What is a leukemoid response?
Neutrophilic leukocytosis with a left shift
What can cause a leukemoid response?
Increased marrow release during strong regenerative RBC response or tissue necrosis
Leukocytosis in dogs with IMHA is correlated with _______ ______.
What platelet abnormality is associated with IMHA patients?
Why do patients with IMHA often have thrombocytopenia?
Immune-mediated platelet destruction and disseminated intravascular coagulation (DIC)
True or false: There are no consistent chemistry abnormalities with IMHA.
What does a biochemistry often reflect in patients with IMHA?
dehydration (elevated bilirubin) and hypoxic damage (mild to moderate elevations)
If there is no red in a urinalysis in a patient with IMHA, what does that indicate?
there is no intravascular hemolysis
True or False: There is a single definitive test for IMHA.
Diagnosis of IMHA is based on a number of findings. Name them.
Anemia with a HCT of < 25-30%
Evidence of hemolysis
Evidence of antibodies against RBCs
Elimination of underlying causes of anemia
An appropriate response to immunosuppressive therapy
What are some hereditary non-immune causes of hemolysis?
Pyruvate kinase deficiency (PK), Phosphofructokinase deficiency (PFK), and hereditary stomatocytosis
What are some acquired non-immune causes of hemolysis?
Toxins - zinc, onions, garlic
Hypophosphatemia - diabetic ketoacidosis or refeeding syndrome
Microangiopathic hemolytic anemia - DIC or heartworm disease
Primary IMHA is what type of hypersensitivity reaction?
type 2 hypersensitivity reaction
What breeds are predisposed to primary IMHA?
Cocker spaniels, Old English Sheepdogs, Poodles, and Dachshunds