Approach to polycytaemia Flashcards
Define polycytaemia/erythrocytosis
Increase in any
- PCV / Htc
- RBC count
- Hb
Increased HCT or RBC count can be relative or absolute, describe each of these
Relative: : proportional changes of RBC numbers in relation to plasma water
Absolute: true increase in RBC numbers due to erythropoiesis i.e. erythrocytosis – plasma volume is normal
What are the two causes of relative polycytaemia/erythrocytosis?
- fluid loss/redistribution => dehydration
- splenic contraction (horses)
What is the effect of relative polycytaemia/erythrocytosis on protein?
Increases in albumin and total protein
How can relative polycytaemia/erythrocytosis be treated?
- correct fluid and electrolyte imbalances
- treat the cause
What is the cause of absolute polycytaemia/erythrocytosis?
Increase in red cell mass due to more RBC production
Compare primary and secondary absolute polycytaemia/erythrocytosis
Primary - independent of erythropoietin
Secondary = dependant on erythropoietin
What are the causes of erythropoietin dependant secondary absolute polycytaemia
- Appropriate (due to generalised hypoxia)
- Inappropriate (not a response to hypoxia)
Appropriate secondary absolute polycytaemia is a response to?
Generalised hypoxia (low SatO2) and hypoxaemia (low PO2)
Appropriate secondary absolute polycytaemia stimulates what to happen?
The kidney to produce erythropoietin which stimulates the marrow for RBC production
What are the causes of inappropriate secondary absolute polycytaemia?
Caused by inappropriately increased EPO
- Renal tumours or other lesions causing localised renal hypoxia (Most common cause)
- Non renal tumours producing EPO or EPO-like substances (Rare)
What is the cause of primary absolute polycytaemia?
- Not caused by increased EPO
- The bone marrow is producing more RBCs without being instructed to do so
How can you treat primary absolute polycytaemia?
Remove the underlying cause if possible
- Stabilise with phlebotomy
If PCV is increased and total protein is within normal limits is it a relative or absolute erythrocytosis?
Absolute
