Polycytaemia

Question 1

Define Polycytaemia

Answer 1

Increase in PCV/Hct, RBC count or Hb.Aka erythrocytosis - Increase in RBC mass

Question 2

In which situations may a increase in the erythron be seen?

Answer 2

• Sighthounds - higher PCV naturally
• Dehydrated patients
• Splenic contraction in horses - physiological (exercise)

Question 3

What is the difference between relative and absolute erythrocytosis?

Answer 3

Relative

• Decreased plasma volume
• Erythrocyte redistribution Absolute
• Actual increase in red cell mass

Question 4

Name and describe some causes of relative polycytaemia due to decreased plasma volume (fluid shift/ dehyd)

Answer 4

Dehydration

• Increasing TP (unless hypoproteinaemia) Acute GI disease
• Fast fluid shift
• May not show dehydration
• eg Haemorrhagic gastroenteritis Severe hyperthermia
• V fast fluid shift
• x dehydration
• eg heat stroke

Question 5

What causes splenic contraction?

Answer 5

ExerciseAdrenaline release - stress

Question 6

What is an ‘appropriate’ causeof secondary absolute polycytaemia?In which clinical conditions may this be seen?

Answer 6

A response to generalised hypoxia (low SatO2)and hypoxaemia (low PO2)

• Severe heart disease - congenital r-l shunt
• Severe lung disease
• High altitude
• Alveolar hypoventilation
• Haemoglobinopathies - inherited/ aquired

Question 7

Causes of aquired chronic haemoglobinopathies…

Answer 7

Chronic CO exposureMethaemoglobinaemia

Question 8

What is an innapropriate secondary cause of absolute polycytaemia?

Answer 8

Increased EPO caused by:

• Tumours causing localised hypoxia
• Tumours producing EPO or EPO-like substances

Question 9

How would relative and absolute polycytaemia be treated?

Answer 9

Relative

• Fluid replacement Absolute
• Remove underlying cause
• Phlebotomy - 10-20mL/kg until resolution