4.3.4: Anaemia - aetiology and pathogenesis Flashcards
How can we detect anaemia on clinical exam?
- Inadequate perfusion/ oxygenation
- Pale mucous membranes
- Lethargy, exercise intolerance
- Compensatory mechanisms e.g. tachypnoea, tachycardia
- Other signs: poor pulse quality, haemic (flow) heart murmur
- Signs related to underlying pathology e.g. pain, icterus, melena
Anaemia
decreased haematocrit (Hct) (a.k.a. Packed Cell Volume, PCV) or haemoglobin (Hb)
Normal PCV dog
35-55%
Normal PCV cat
25-45%
Why is it useful to compare PCV to TP?
- TP is useful to combine with PCV to give us an idea of hydration status
- e.g. if animal with tacky mm and high TP (suggests dehydration) also have PCV on very low end of normal, we might suspect that if properly hydrated, the animal would be anaemic
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Normal
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What are some non-pathological causes that lead to apparent anaemia?
- Splenic relaxation e.g. anaesthetic agents -> sequestration of RBCs in spleen
- Physiologic anaemia in young animals due to rapid growth rate with haemodilution from plasma volume expansion, dilutional from ingested colostrum, destruction of foetal RBCs and low EPO in first few months of life
- Overhydration will dilute the RBCs present and falsely lower the PCV
What are the broad causes of anaemia?
RBC loss due to trauma or coagulopathy.
RBC destruction in haemolysis - could have immune-mediated/ infectious/ toxic cause
Reduced RBC production by bone marrow - could have genetic/ immune-mediated/ chronic disease/ nutritional (iron-deficiency anaemia) and other causes
Mean corpuscular volume (MCV)
average RBC size
Mean corpuscular haemoglobin concentration (MCHC)
the amount of haemoglobin in RBCs; will be affected by any changes in cell volume too
Hyperchromic
MCV above reference interval (i.e. high Hb)
* Usually a false increase because cells can’t pack in more Hb than usual
* e.g. lipaemia can falsely elevate Hb concentration relative to the PCV, thus falsely increasing the MCHC
Polychromatic
lots of colours/ variability of RBC colour
Normochromic
MCHC within the reference interval
Hypochromic
Lighter in colour/ MCHC below the reference interval
How can you decide if an anaemia is regenerative or not?
- Presence of immature, anucleate RBCs -> reticulocytes
- Nucleated RBCs (nRBCs) are more common in regenerative anaemia
- Basophilic stippling = blue dots in cytoplasm of RBCs which correspond to ribosomes not present in mature RBCs -> seen more in regenerative anaemia
- Howell-Jolly bodies -> seen more in regenerative anaemia
- Increased numbers of Heinz bodies -> seen more commonly in regenerative anaemia