approach to erythrocytosis/ polycythaemia

erythrocytosis

increase in RBC mass

• PCV

• RBC count

• HGB

relative vs absolute

relative = proportional changes of RBC mass in relation to plasma water

• dehydration

• splenic contraction and release of RBCs

absolute = true increase in RBC mass due to increased erythropoiesis

normal breed-specific variation

• sighthounds/ other breeds have higher HCT

Relative erythrocytosis- Decreased plasma volume due to dehydrationrel

GI disease, water deprivation, severe hyperthermia

Clinical signs of dehydration and fluid loss (e.g. vomiting, diarrhoea)

TP/ALB often increased with dehydration

Correct fluid and electrolyte imbalances

Treat the cause

relative erythrocytosis - RBC redistribution due to splenic contraction

Adrenalin release (e.g. fear, excitement)

Exercise

Only modest HCT increase

Transient

Physiological leukocytosis?

Thrombocytosis?

No clinical consequences

absolute erythrocytosis

Caused by a real increase in RBC mass

Secondary due to increased EPO

• Appropriate (due to hypoxia)

• Inappropriate (not a response to hypoxia)

Primary

• Not due to increased EPO

• Chronic myeloproliferative disease

Clinical signs of hypervolaemia and hyperviscosity

appropriate secondary erythrocytosis

Response to generalised hypoxia (low SatO2) and hypoxaemia (low PaO2)

Appropriate secondary erythrocytosis - examples

inappropriate secondary erythrocytosis examples

Primary erythrocytosis

Not caused by increased EPO

Chronic myeloproliferative disease

• Due to a mutation in the JAK2 gene (humans and dogs)

• Very rare

Diagnostic algorithm for erythrocytosis

Treatment of absolute erythrocytosis

Remove the underlying cause if possible

Stabilise with phlebotomy

• 15-20 ml/kg until resolution of clinical signs and HCT < 55% in dogs, <50% in cats (60-65% can be acceptable if cyanotic cardiac disease)

• Care maintaining normovolaemia

• Can be repeated every 4-8 weeks

• Myelosuppressive therapy (hydroxyurea) in case phlebotomy not effective (required more than once every 4 weeks)