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Immune-Mediated Hemolytic Anemia (IMHA)

Written by: Brigid L.


History

  • Lil Bit is a 6 year old intact female Shih Tzu previously diagnosed with Immune-Mediated Hemolytic Anemia in 2013.
  • Lil Bit presented at her rDVM for lethargy and lack of coordination, or ataxia. Referred to IVS for anemia noted during bloodwork.

Physical Exam

Abnormalities noted:

  • Minimally responsive
  • Extremely pale mucous membranes (gums)
  • Tachycardic (abnormally high heart rate) with grade 3 murmur

Diagnostic Results

Due to Lil Bit’s extreme presentation, only diagnostics to determine red blood cell (RBC) numbers were performed immediately. This was performed to determine her need for a blood transfusion.

To determine RBC counts in a blood sample, a small amount of blood is added to a capillary tube and spun in a centrifuge for 3 minutes. Once spun down, the RBCs will be separated out at the bottom of the tube. This is measured as a percentage. The plasma, containing the blood proteins, sits on top. The tube is broken and plasma put into a refractometer to get the total protein.

Packed Cell Volume (PCV) or Hematocrit (Hct): volume percentage of red blood cells (RBCs) in blood—normal values for dogs is between 35- 45%.

  • PCV at presentation was 9% indicating severe anemia, or lack or RBCs

Total Protein (TP): measures the amount of total protein in the blood—normal values are between 6.5-8 gm/dl

  • TP at presentation was 8.2 gm/dl indicating slight dehydration

Diagnosis

Immune-Mediated Hemolytic Anemia (IMHA): a disease common to dogs in which red blood cells are destroyed by the immune system

  • Many causes: Autoimmune (Primary), toxicity, infectious, neoplasia
  • Diagnosis: Anemia with strong regenerative response, Coomb’s test, Agglutination

Lil Bit had been previously diagnosed with Primary IMHA in 2013. With her severe anemic presentation, it was concluded she was likely in IMHA relapse.

Treatment

Lil Bit presented with a dangerously low PCV at 9%. At that percentage, Lil Bit had very little red blood cells circu- lating throughout her body. RBCs are extremely important to keep the body oxygenated. A lack of RBCs leaves the body unable to perform its normal functions. This can cause extreme lethargy and weakness, as well as, an abnor- mally high heart rate as the body tries its hardest to circulate what RBCs are present as quickly as possibly. Lil Bit’s anemic state needed to be addressed immediately.

Blood Transfusion
Lil bit was prepped for a blood transfusion. A small amount of Diphenhydramine antihistamine was given intra- muscularly to help mediate any possible hypersensitivity reaction she may have to the donor blood. Dexame- thasone Sodium Phosphate, a steroid, was administered intravenously as a way to begin immune suppression and stop the immune-mediate hemolysis.

Prior to the blood transfusion, Lil Bit’s blood was cross matched with the donor blood to check for possible reac- tions. This is particularly important in dogs that have had prior transfusions. Dogs previously exposed to donor blood are at risk for more severe immune reactions. Lil Bit’s blood had no major reaction in the cross match test. A transfusion of 31 ml total volume RBCs was started.

Typically, blood transfusions are given slowly over a four hour period. In this case, Lil Bit suffered from a transient ischemic event shortly after the transfusion began. Due to her low red blood cell count, she could not properly oxy- genate. As a result, she stopped breathing and developed a dangerously low heart rate. Once she was stabilized, the 31 mL transfusion was quickly administered as a bolus as an extreme measure to help her body oxygenate properly.

Medications
Once Lil Bit was stabilized and able to take oral medications, the following medications were prescribed to manage her IMHA.

Prednisone: a steroid that acts as an immunosuppressive agent that helps suppress the body’s reaction to its own red blood cells. This is often used as the starting medication in IMHA cases. Depending on the case, Prednisone can be used short-term until the symptoms have resolved or used lifelong. If this medication is discontinued, it requires a slow tapering dose.

Azathioprine: a second-line immunosuppressive drug often used in conjunction with Prednisone. Azathioprine has a slow onset of act taking about 1 week to reach full effect. It is used as a long-term management drug for IMHA. It may be discontinued after remission is achieved.

Clopidogrel: a platelet aggregation inhibitor that can be used in dogs with IMHA to treat hypercoagulable states. Lil Bit had an abnormally high platelet count that can lead to hypercoagulability, or a state in which blood clots form too easily. If a hypercoagulable state is not managed properly with medication, the blood clots can stop blood flow to areas of the body leading to severe complications. Clopidogrel would help keep her from forming blood clots in the future.

Famotidine: is a gastrointestinal medication to help reduce acid production in the stomach. This was prescribed to help prevent ulcers that long-term Prednisone use can cause.

Prognosis

Prognosis for dogs diagnosed with IMHA is guarded. Ranges of 26-70% mortality rates have been reported in dogs with Primary IMHA. Prognosis improves if the animal survives the first two weeks after an anemic crisis.

Prognosis for recurrent episodes is guarded to poor as transfusions become more complicated.


References:

  • Nelson, RW, Couto, CG. Small Animal Internal Medicine (5th Ed). St. Louis, Missouri: Elsevier Saunders pp 1417- 1421.
  • Plumb, DC. Plumb’s Veterinary Drug Handbook. (8th Ed). Ames, Iowa: Wiley Blackwell.
  • Sharp C, Kerl ME. Immune-Mediated Hemolytic Anemia. Standards of Care: Emergency and Critical Care Medi- cine 2008: 1-6.
  • Tilley, LP, Smith, FWK. Blackwell’s Five-Minute Veterinary Consult: Canine and Feline (6th Ed). Ames, Iowa: Wiley Blackwell.

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