Anaemia in small animals

• What is the definition of anaemia?

  A decreased haematocrit (HCT/Hct) or packed cell volume (PCV) or haemoglobin (Hb).
• What is a haematocrit?

  A calculated value from the mean cell volume and red blood cell count, and haemoglobin concentration, which are provided by automated analysers. Hct can be affected by machine errors.

  HCT = (MCV x RBC) + 10.
• What is PCV?

  Packed cell volume

  A directly measured value measured as a percentage of packed red cells in blood volume. PCV can be affected by how RBCs pack together.
• How do we detect and confirm anaemia?

  Anaemia may be suspected during clinical examination. Signs that may be seen include.

  Inadequate perfusion/ oxygenation:

  • Pale mucous membranes
  • Lethargy, exercise intolerance

  Compensatory mechanism:

  • Tachypnoea, tachycardia

  Other signs:

  • Poor pulse quality.
  • Haemic/ flow heart murmur.

  Signs related to underlying pathology:

  • Splenomegaly, lymphadenopathy, pain, pic, icterus, melaena.
• Categorising anaemia - severity

  Quite arbitrary.

  Does not necessarily relate to clinical condition (chronicity may do more so).

  Can be useful during diagnosis of cause, e.g. a severe anaemia would rarely be due to anaemia of chronic disease.
• Categorising anaemia - RBC indices

  We can categorise RBCs by size, colour, shape and cellular contents.

  Mean corpuscular volume (MCV)

  • The average volume of the RBCs will change if large/small RBCs are present.

  Mean corpuscular haemoglobin concentration (MCHC):

  • The amount if haemoglobin of RBCs will change dependant on absolute amount of Hb but also if affected by cell volume.
• Definition of normocytic

  MCV within the reference interval.
• Microcytic definition

  Small cells; MCV below the reference interval.
• Definition of Hyperchromic

  More colour, darker in colour; MCHC above the reference interval. Usually a false increase (not a true in Vivo finding), e.g. lipaemia can falsely increase the haemoglobin concentration relative to the HCT, this falsely releasing MCHC.
• Definition of polychromatic

  Lots of colours, many colours; there is variability of RBC colour.
• Definition of Normochromic

  MCHC within the reference interval.
• Definition of Hypochromic

  Lighter in colour, less colour; MCHC below the reference interval.
• Categorising anaemia - regeneration

  Are there cells that suggest the bone marrow is trying to correct the reduced RBC number?

  • Reticulocytes
  • Anisocytosis (variable size of RBCs)

  Non-specific RBC indicators common (but not always) in regenerative anaemia:

  • Nucleated RBCs (nRBC) - RBC much smaller than WBC.
  • Basophillic stippling - nuclear remnant (dot within the RBC).
  • Howell-Jolly bodies
  • Heinz bodies
• Causes of regenerative anaemia

  Likely due to haemorrhage or haemolysis
• Causes of non-regenerative anaemia

  Decreased bone marrow production of RBCs.

  Pre-regenerative anaemia (early). The bone marrow takes 3-5 dast ti respond to anaemia so acute conditions may initially appear non-regenerative.

  Chronic haemorrhage or haemolysis that was regenerative will eventually become non-regenerative.
• What are Acanthocytes (spur cells)

  Irregular, blunt tipped spicules.

  Liver disease (due to alterations in lipid metabolism);

  Fragmentation injury - clots/ DIC; fragile RBCs (e.g. Iron deficiency).
• What are echinocytes (burr cells)

  Sharp or blunt projections, tend to be uniform and evenly spaced.

  Artifact.

  Drug exposure (e.g. fursemide, doxorubicin).

  Electrolyte disturbance (typically low IC K+).

  Renal disease, especially golerulonephritis (unknown mechanism).

  Snake envenomation (form due to phospholipases in the venom).

  
• What are Schistocytes?

  RBC fragmetns.

  Mechanical injury; often some level of vascular damage e.g. DIC, glomerulonephritis, vasculitis, PSS, vascular neoplasms.
• What are Spherocytes?

  Sphere shaped, no central pallor, smaller and more dense than a normal RBC.

  Normal-ish volume (MCV is normal).

  Moderate to severe spherocytosis - IMHA; low-moderate numbers - can be other things.

  
• What are the main causes of anaemia?

  RBC loss:

  • Haemorrhage due to trauma or coagulopathy;
  • Internally e.g. GIT, parasites, pulmonary, abdominal cavity.
  • Externally e.g. wounds, epistaxis.

  RBC destruction:

  • e.g. haemolysis
  • From toxicity, infection, immune-mediated, mechanical damage.

  Reduced RBC production:

  • By the bone marrow;
  • Genetic, immune-mediated, infectious chronic disease/ inflammation, nutritional deficiencies (iron-deficiency anaemia), myelodysplasia.
• Causes of anaemia - blood loss and haemorrhage

  Could be acute and spectacular - traumatic wounds, blunt force (intracavity bleeding), diarrhoea and vomit (haemorrhagic diarrhoea, haematemesis), epistaxis, DIC.

  Could be mild or chronic - melaena, chronic or multiple small wounds, GI or blood-borne parasitism.

  No blood loss will result in immediate drop in PCV.

  All blood loss is non-regenerative to begin with.

  Iron deficiency may result if blood loss becomes very prolonged.
• Haemolysis causes of anaemia

  IMHA is a common cause of haemolysis seen in clinical practice.

  Reaction to normal self antigen (Ag);

  • Primary immune system dysfunction and loss of tolerance.
  • Antigen exposed due to cell damage.
  • Similarity between self Ag and foreign Ag (e.g. infectious agent or drug)

  Reaction to infectious agents bound to cell surface.

  Reaction to non-biological Ag bound to cell surface (e.g. drug, toxin).

  Pyrexia, pallor/ jaundice, CV abnormalities

  Spherocytes, leucocytosis, thrombocytopaenia, RBC parasites.
• How do we treat anaemia?

  Triage and emergency treatment, investigation and stabilisation.

  Fluid therapy, blood product transfusion if needed.

  Treat (or limit the symptoms of) the specific disease:

  • Haemorrhage
  • Haemolysis
  • Infectious diseases
  • Oxidative damage
  • Bone marrow
• Emergency stabilisation of the anaemic patient

  1. Oxygen supplementation

  2. Temperature management - often after trauma animals are quite cold, be careful warming them up as they can vasodilator which will decreased their BP, so warms up slowly with appropriate fluids if necessary

  3. Fluid therapy

  4. Analgesia
• Treat cause/concurrent conditions

  1. Confirm and characterise anaemia

  2. TFAST, radiographs, AUS

  3. Full biochemistry and haematology (looking at renal parameters, possible haemocrit to check PCV)

  4. Infectious disease screening e.g. FIV, FeLV, 4DX (Ehrlichia, Anaplasma, HW, Babesia)
• Emergency surgery may be warranted e.g. for bleeding haemangiosarcoma, splenic rupture, arterial bleeds
• Babesia

  Intracellular protozoan; transmitted by ticks, worldwide spread but not endemic here.

  IV and EV haemolysis - pallor, jaundice.

  Pyrexia, haemoglobinuria, CV compromise, weakness, inappetence.

  Microscopy (false negatives) vs PCR.

  Treatment:

  • Imidocarb (unlicensed), Azythromycin, Doxycycline are all effective.
  • Supportive treatment including transfusions, liver support.
  • Should show clinical improvement in 1-2 days, treatment may result in remission rather than a cure.
• Oxidative damage

  Heavy metals (zinc, copper) - more common in farm animals, especially as sheep are most susceptible.

  Alliums (onions, leeks, garlic) - Japanise dog breeds and cats more susceptible.

  Drugs - main one in small animals is paracetamol.
• Ehrlichia in anaemia

  Rickettsial bacteria transmitted by ticks, inside macrophages and monocytes.

  • Grumbling thrombocytopaenia.
  • Hypoglobulinaemia
  • Vague depression, fever, weight loss, poor appetite.
  • Enlarged lymph nodes.
  • Epistaxis, Petechiae, ecchymoses.

  When in acute phase will often recover but can develop to a chronic infected state.
• Chronic monocytic ehrlichia (CME)

  Profound thrombocytopaenia.

  Failure of bone marrow - non regenerative anaemia, other cytopaenias.

  Emaciation

  Swelling of hind legs and scrotum - PLN.

  Thrombocytopaenia - uveitis, neutering signs.

  Hypoglobulinaemia -> glomerulonephritis