The term polycythaemia has traditionally been used to described disorders in which there is an increase in the number of red cells resulting in a persistently raised haematocrit. However, since usually only red cells are involved erythrocytosis is a more accurate term, and polycythaemia should really be reserved for polycythaemia vera which involves 3 cell lineages.
Erythrocytosis is defined as a raised haematocrit >0.52 in men or >0.48 in women for >2 months
It may be subdivided into
- primary polycythaemia (=polycythaemia rubra vera)
- secondary erythrocytosis
- apparent erythrocytosis
The initial investigations on a finding of erythrocytosis should be
- History and examination
- FBC and blood film
- JAK2 mutation
- Serum ferritin
- U&Es and LFTs
If the JAK2 is negative and there is no obvious secondary cause the next line of investigations should be:
- Red cell mass
- Arterial oxygen saturation
- Abdominal ultrasound
- Serum erythropoietin level
- Bone marrow aspirate and trephine
- Cytogenetic analysis
- BFU-E culture
Primary polycythaemia
- Presentation
- Thrombosis
- Pruritus after baths
- Burning pain in distal extremities
- Splenomegaly
- Weight loss
- Sweating
- Plethora
- Haemorrhagic events
- Gout
- Diagnostic criteria are:
- If JAK2 positive (= around 95%)
- High haematocrit (>0.52 in men, >0.48 in women) OR raised red cell mass (>25% above predicted)
- If JAK2 negative
- Raised haematocrit >0.60 in men or 0.56 in women OR raised red cell mass >25% above predicted AND
- No cause of secondary erythrocytosis
- Then either
- Palpable splenomegaly OR
- presence of an acquired genetic abnormality (excluding BCR-ABL) in the haematopoietic cells OR
- 2 of
- Thrombocytosis (platelet count >450x10^9/l)
- Neutrophil leukocytosis (neutrophil count > 10 x10^9/l in non-smokers or 12.5x10^9/l in smokers
- Radiological evidence of splenomegaly
- Endogenous erythroid colonies or low serum erythropoietin
- Management
- Venesection – maintain haematocrit at less than 0.45
- Aspirin 75mg od unless contraindicated
- Cytoreduction (interferon or hydroxycarbamide = hydroxyurea) should be considered if
- Venesection isn’t tolerated
- Symptomatic or progressive splenomegaly
- Thrombocytosis
- Evidence of disease progression, eg weight loss, night sweats
Secondary erythrocytosis
- Causes
- Hypoxia
- COPD
- High altitude
- Cyanotic congenital heart disease
- Renal pathology
- Polycystic kidneys
- Hydronephrosis
- Renal artery stenosis
- Erythropoietin-secreting tumours
- Hepatoma
- Fibroids
- Cerebellar
- Hypernephroma
- Phaeochromocytoma
Apparent erythrocytosis
- Apparent erythrocytosis is defined as raised haematocrit but normal red cell mass.
- Possible causes for apparent erythrocytosis include:
- Physiological variant
- Obesity
- Smoking
- Alcohol
- Renal disease
- Hypertension
- Diuretics
- If the apparent erythrocytosis is due to decreased plasma volume (ie dehydration) it is called relative erythrocytosis.
- Management
- Reduction of risk factors
- Consider venesection if
- Recent history of thrombosis or risk factors for thrombosis
- Haematocrit >0.54
References
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