Canterbury DHB

Investigation of Suspected PV

An algorithm for investigating suspected PV is suggested on UpToDate – Diagnostic approach to the patient with polycythemia. Bone marrow aspirate, trephine and cytogenetics are not required to diagnose PV, but may be useful in distinguishing between early PV, essential thrombocythemia (ET) (both of which can be associated with thrombocytosis), and early-stage primary myelofibrosis (PMF).

For a discussion of the role of bone marrow histopathology in MPN, see Thiele J, et al. (2005) pages 184–95³.

The British Committee for Standards in Haematology⁴ suggests a similar diagnostic approach.

Note – Red cell mass and endogenous erythroid colony studies are not locally available. A study from the Mayo Clinic found raised red cell mass in all patients with Hct >0.55 and ).50 in men and women respectively.

Non-PV erythrocytosis

If no JAK2 mutation can be found, and serum epo is normal to elevated, PV is virtually excluded. Consider other causes of erythrocytosis:

• hypoxia – CXR, arterial oxygen saturation and/or pulse oximetry, sleep studies, etc.
• renal disease – tumour, local renal hypoxia
• congenital disorders – Hb mass spectroscopy, p50, rare germline mutations.
• exogenous epo use
• other epo (or epo-like) secreting tumours

In patients who have had PV excluded, erythrocytosis may be categorised as:

• non-secondary erythrocytosis – a true increase in red cell mass due to a circulating stimulatory factor, usually erythropoietin, secondary either to a renal tumour or hypoxia.
• apparent erythrocytosis – caused by a reduction in plasma volume without a true increase in red cell mass. This has also been referred to as:
  • stress erythrocytosis
  • spurious polycythaemia
  • Gaisböck’s syndrome
  • pseudo-polycythaemia
• combined polycythaemia – both reduced plasma volume and increased red cell mass. This combination is seen most commonly in smokers.

In such cases, management is directed at the underlying cause so is not typically managed in a haematology clinic. Most patients without PV do not require venesection unless symptomatic, or unless haematocrit is >0.6.

Individualise management for patients with very high haematocrits and, if attempting venesection, monitor treatment closely to ensure it is proving beneficial.

Venesection has not been shown to reduce stroke risk in patients with increased red cell mass secondary to cyanotic heart disease⁵. By extrapolation, no benefit is expected in patients with elevated red cell mass due to hypoxia in other situations, e.g. smokers.

Topic Code: 6654