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What is anemia?

A reduction in erythrocyte number and or the hemoglobin concentration. 

i.e. decreased RBC, HCT/ PCV and or Hb


Anemia is not a final diagnosis it is a clinical symptom. Must find the underlying cause.  


What are clinical features of acute anemia? 

  1. Pallor
  2. tachycardia
  3. muscular weakness
  4. subnormal temp
  5. coma
  6. death


What are the clinical features of chronic anemia? 

  1. Fatigue 
  2. lethargy
  3. exercise intolerance
  4. tachycardia
  5. faitning
  6. pallor
  7. cardiac murmur (not due to valve defect, but due to decrease blood rbc, therefore decrease viscosity, increase in turbulence, and murmur ensues. 


Anemia can be caused by what two simple ideas? 

  1. A decrease in erythrocytes entering the blood ( i.e. decreased production/ Bone marrow issues)



  1. An increase in erythrocytes exiting the blood. If BM is functioning normally you will see an increase in reticulocytes in the blood due to regeneration. 


Describe the two different anemic processes. 

1. Non-Regenerative Anemia: Decrease in RBC production. 

  • Can be Primary or Secondary disorder
  • The primary disorder is a true bone marrow dysfunction. 
  • The secondary disorder could be due to renal failure which causes a decrease in EPO which would cause a decrease in erythrocyte production. 


  1. Regenerative Anemia: Increase in RBC exit/ turnover. 
  • Hemolytic: Increase destruction due to intravascular or extravascular lysis. 
  • Hemorrhagic: Internal or External 


How can we tell if the anemia is regenerative? 

  1. Reticulocytes in the blood (NOT IN HORSES--- NO IMMATURE RBC'S IN CIRCULATION)
  2. Macrocytic hypochromic:
  • This causes an increase in MCV (because there are increasing #'s of reticulocytes which are bigger than RBC's) 
  • Causes a decrease in MCH and MCHC because the Hb concentration is decreased. 

Hypochromic indicates an increase in central pallor due to a decrease in Hb. 


  1. Increase polychromasia/ anisocytosis: polychromasia is just reticulocytes and anisocytosis is irregular shapes and sizes of the RBC's. The reason for anisocytosis is because the reticulocytes are bigger than RBC's and are maturing into them (shrinking) therefore we are seeing different sizes due to maturing. 
  2. Basophilic stippling: small dots located at the periphery of the RBC (found in cattle) 


Describe Hemorrhagic anemia. Acute? Chronic? Internal/ External? Coagulopathies?

Blood loss that can be internal or external. 

Acute: after accidents or sx. procedure

Chronic: Bleeding from ulcers, neoplasms, parasitic. 

Coagulopathies: Rat bait. Clotting disorders. 

Internal: not losing Fe to outside therefore can be recycled to make new RBC's

External: Lose iron to outside environment. Cannot be recycled. Less RBC's formed. 


What blood findings would we see in Hemorrhagic Anemia? 

  1. Blood findings are normal in the first few days/ pre regenerative
  2. Regenerative findings
  • polychromasia
  • Howell Jolly bodies (Black nuclear remnants from normoblasts) 
  • Anisocytosis
  • Thrombocytosis
  • Neutrophilia 

These all lead to macrocytic hypochromasia. 


The degree of regeneration in Hemorrhagic Anemia depends on what? Along with the loss of RBC's what else does the body lose? 

  1. Severity of blood loss
  2. location of bleeding (vascular v. avascular)
  • Internal v. External
  • Internal bleeding allows Fe to be recycled to assist in Hb synthesis allowing a greater regeneration. 

Proteins, not just RBC's are being lost causing hypoproteinaemia (panhypoproteinaemia) 


What are two very important features of Hemolytic Anemia? 

  1. Reduced blood cell survival time
  2. Iron from destoryed erythrocytes is retained in the body ( increases regeneration) 


Destruction of the RBC's reduces the RBC's survival time. 


What are the methods of RBC destruction in Hemolytic Anemia? 

  1. Intravascular lysis: in the blood stream
  2. Extravascular lysis: damaged RBC's are phagocytosed by Macrophages in the spleen. (Erythrophagocytosis) 


Describe the process of Extravascular Lysis. 

  • Extravascular hemolysis is a physiologic process that is always occurring to some degree in the body when effete RBC's are phagocytosed by macrophages in the spleen, liver, or bone marrow. 
  • With extravascular hemolysis, the erythrocytes are degraded within macrophages, so hemoglobin is not released free into the cytoplasm. Thus, we do not see hemoglobinemia or hemoglobinuria with extravascular hemolysis alone, unless it is accompanying intravascular hemolysis.
  • Phagocytosis of RBC will lead to splenic enlargement and will break them up into Iron and globin. Iron will be recycled by entering the plasma, binding to the transport protein apotransferrin which will transport it into the bone marrow for Hb production. 
  • Heme from RBC breakdown will be oxidized into biliverdin, which is then reduced to bilirubin. Bilirubin is H20 insoluble. Bilirubin will enter the plasma circulation and bind to albumin which will transport it to the liver. Bilirubin in circulation will cause jaundice if in excess. 
  • When bilirubing is in the liver it undergoes conjugation via glucuronidation to become water soluble to allow for excretion in the bile. 


Describe the process of Intravascular hemolysis. 

  • Intravascular hemolysis results from the rupture or lysis of red blood cells within the circulation, i.e. the red cells are lysing in vivo.
  • The rupture of the RBC membrane releases free Hb. Excess Hb dimers in the plasma will cause a Hemoglobinemia. 
  • Free Hb in the circulation will bind to haptoglobins which will either:

    1. Become phagocytosed by macrophages and release heme which become unconjugated bilirubin which will travel to the liver for conjugation and excretion in the bile. 

    2. Become saturated and travel to the liver where the complex is broken down into Heme, globins, and Fe. Fe is recycled, heme becomes conjugated, and globins are broken down into AA for protein synthesis. 
  • Excess Hb Dimers in the blood (not bound to haptoglobins) will either:

    1.  Will cause a hemoglobinemia in the blood. 

    2. will travel to the kidneys causing a hemoglobinuria. Hemoglobin in the kidneys is toxic and cause a "Toxic Nephrosis" 


What are the four acquired causes of Hemolytic anemia?

  1. Toxic (oxidative compounds)
  2. Infectous agents
  3. Fragmentation (trauma)
  4. Immune-mediated. 


What are inherited causes of hemolytic anemia? 


  1. Phosphofructokinase deficiency in spring spaneils. 
  2. Pyruvate kinase deficiency in Basenjis. 


What are infectious causes of Hemolytic Anemia?

  1. Mycoplasma spp. 
  2. Babesiosis 


What are toxic and oxidative causes of Hemolytic Anemia? 

  • oxdiative agents in drugs/ chemicals can reduce GLUTATHIONE levels on RBCs.
  • Heme iron oxidized to METHEMOGLOBIN. 
  • Oxidative damage to hemoglobin causes HEINZ BODY FORMATION. 
  • Destroyed by intravascular or extravascular hemolysis. 


When are Heinz bodies see physiologically rather than due to oxidative damage? 

Cats will sometimes shows physiologic Heinz bodies in their RBCs due to a different Hb structure. 


What stain can be used to identify Heinz bodies? 

NMB- New Methylene Blue


What are some examples of drugs, elements, and foods which would cause Toxic/ oxidative hemolytic Anemia? 

  • copper posioning
  • zinc
  • brassicas
  • red maple
  • snake venoms
  • onions
  • paracetamol 


What are the causes of Fragmentation Hemolytic Anemia? 

  • RBCs are subjected to excessive trauma in circulation.
  • Features of intravascular lysis may be present. 
    - Hemoglobinemia
  • Schistocytes-fragmented part of a RBC, usually irregularly shaped and jagged and have two pointed ends. 
  • Acanthocytes- spiked cell membrane " spur cells" 
  • Small vessel disorders: microangiopathic. 
  • Large vessel disorders. 


What is an example of why fragmentation of RBCs could occcur? 

  • A lesion in the heart valves stops the heart valves closing there increasing turbulence, cuasing an increasing of bashing of red cells cuasing mechanical trauma. 


What causes Immune Mediated Hemolytic disorders?

  • Blood group incompatibilities
    - Blood transusion reactions

  • Immune mediated hemolytic anemia generated against self anitgen/ own red cells. 


Describe Hemolytic Disease of the Newborn


Maternal blood group anitbodies will be absorbed from the colostrum and destroy the neonates RBC's via phagocytosis/ intravascular lysis. 

This occurs when the mother has a different blood type than the foals (the new born has inherited the fathers blood group) 

The dam has a sensitization to that blood type due to a previous pregnancy, vaccines, or blood products.

Therefore she will form alloantibodies to that specific foreign antigen. 

Signs will develop 12-48 hours after birth. 


What causes Immune Mediated Hemolytic Anemia in Adults? 

  1. Primary: Idiopathic (autoimmune)
  2. Secondary: underlying trigger. 
    - Drugs/ toxins
    -infectious agents
  3. Dogs often pimrary idiopathic/ automimmune 
  4. Other species: uncommon, usually secondary 


Describe Canine Autoimmune Hemolytic Anemia. 

  • Production of autoantibodies against own RBC. 
  • IgM or IgG or BOTH. 
  • Autoantibodies may be agglutinins (clumping) or lysins (lyse) or incomplete in triggering the complement cascade. 
  • IgG-Monomor- Y shaped. 
  • IgM-Pentamer- many hands. 


Warm Antibody AIHA

  • Reacting at body temperature. 
  • The IgG antibodies attach to a red blood cell, leaving their FC portion exposed with maximal reactivity at 37°C (versus cold antibody induced hemolytic anemia whose antibodies only bind red blood cells at low body temperatures, typically 28-31°C). The FC region is recognized and grabbed onto by FC receptors found on monocytes and macrophages in the spleen. These cells will pick off portions of the red cell membrane, almost like they are taking a bite. The loss of membrane causes the red blood cells to become spherocytes.
  • Incomplete IgG coats the RBC. 
  • Becomes complete or partially phagocytosed in the spleen my macrophages causing a splenomegaly or spherocytosis. 
  • May partially activate complement- C3b which opsonizes coated cells removed by macrophages. 


What is spherocytosis?

  • Seen in Autoimmune hemolytic anemia.
  • The increase in production of erythrocytes that are sphere shaped rather than bi concave discs. 
  • no area of central pallor 


Why does Autoagglutination occur? 

A high concentration of IgG or warm reactive IgM antibodies will cause the clumping of RBCs. 


The Slide Agglutination Test:

This test demonstrates the presence of antibody on RBC's. It is the best method to differentiate rouleaux formation (which occurs due to increased viscosity) and agglutination. Adding a drop of saline and a drop of blood to the slide. The saline will decrease the viscosity of the blood therefore separating rouleaux formation. If the cells stay clumped then agglutination is occurring due to the presence of IgM coating the red cells. 


the Direct Coombs Test

In certain diseases or conditions an individual's blood may contain IgG antibodies that can specifically bind to antigens on the RBC surface membrane, and their circulating RBCs can become coated with IgG alloantibodies and/or IgG autoantibodies. Complement proteins may subsequently bind to the bound antibodies and cause RBC destruction.

The direct Coombs test is used to detect these antibodies or complement proteins that are bound to the surface of red blood cells; a blood sample is taken and the RBCs are washed and then incubated poly specific serum (Coombs reagent). If this produces agglutination of RBCs, the direct Coombs test is positive, a visual indication that antibodies (and/or complement proteins) are bound to the surface of red blood cells.