Investigations and diagnosis

Persistently raised haematocrit M >0·52, F >0·48

Clinical history/examination/1st line investigaions includes EPO

May identify Clear secondary cause - if not then check JAK2 V617F mutational analysis (PB) - if positive then diagnose PV

• significant, JAK2-unmutated erythrocytosis.
• consider red cell mass to confirm (if Hct<0·6/0·56)
• consider USS abdomen

Is there a likely secondary cause from clinical history, stage 1/2 investigations, USS abdomen

statify by serum erythropoietin

• if serum erythropoetin is normal or low then JAK2 exon 12 mutation analysis; consider bone marrow biopsy

Stage 1 Investigations

Full blood count/blood film, Renal and liver function, Arterial oxygen saturation (SaO2)/carboxyhaemoglobin, Serum ferritin, Serum erythropoietin, JAK2 V617F mutational analysis

• Full blood count/blood film
  • full blood count analysis will not only confirm a raised Hct but will also identify neutrophilia and thrombocytosis - are common in JAK2 V617F-positive PV and part of
    the criteria for JAK2-negative PV
    • smokers have a significantly higher neutrophil count than non-smokers - neutrophilia is defined as>12.5x 10^9/l in this patient group
      
      
• blood film
  • if confirmed PV, abnormalities, such as circulating blasts, leucoerythroblastic features and monocytosis, would be indications for bone marrow assessment
    
    
• renal, liver function, bone profile
  • various renal and hepatic diseases can cause erythrocytosis
  • serum calcium levels should also be determined to exclude a parathyroid adenoma/carcinoma - rare causes of secondary erythrocytosis

Erythropoetin

• high EPO levels
  • may occur in hypoxic conditions or when erythrocytosis is secondary to exogenous administration or endogenous overproduction
• EPO levels are typically low in PV

Serum ferritin

• low serum ferritin levels are common in PV patients and iron deficiency can mask the presentation of PV > giving a misleadingly low Hct because iron deficiency limits erythropoiesis and hypochromic microcytosis develops.

JAK2 V617F mutational analysis

• identification of JAK2 mutations in almost all PV patients has revolutionised the diagnosis of PV. The JAK2 V617F mutation can be found in over 95% of PV patients and an exon 12 mutation in most remaining patients
  • testing for JAK2 V617F in peripheral blood is sensitive and bone marrow samples are not required to identify this
  • testing for JAK2 V617F is advised as a stage 1 investigation and should confirm the diagnosis the vast majority of PV patients.

2) Further investigations in JAK2 V617F-negative erythrocytosis

Further investigations are warranted in those patients with a persistent, significant erythrocytosis if JAK2 V617F studies are negative and a secondary cause is not immediately apparent. Secondary causes must be considered because PV is rare in the absence of a JAK2 V617F mutation

Red cell mass studies

• patients with Hct >0.60 (males) or >0.56 (females) can be assumed to have an absolute erythrocytosis, but in others RCM studies can be helpful to confirm an absolute erythrocytosis
• an RCM more than 25% above the mean predicted value is diagnostic of an absolute erythrocytosis

Those with a raised Hct but an RCM within the normal range have an apparent erythrocytosis.

• a relative erythrocytosis, found in states of dehydration, can be confirmed when the RCM is within the normal range and plasma volume is below normal
• patients with a relative or apparent erythrocytosis require no further investigation

Abdominal ultrasound

• radiological splenomegaly is a minor criterion for JAK2 V617F-negative PV and ultrasound is the simplest method for detection
• can also exclude secondary causes of erythrocytosis, particularly renal and hepatic pathology, including hepatocellular carcinoma

Further testing can be stratified according to the EPO level measured during stage 1 investigations

Normal or low EPO level

JAK2 exon 12 analysis

• compared with JAK2 V617F, patients with exon 12 mutated- PV tend to be
  • younger,
  • with higher haemoglobin concentrations,
  • lower white blood cell (WBC) and platelet counts, and
  • an isolated increase in erythropoiesis without granulocytic or megakaryocytic morphological abnormalities

In contrast to JAK2 V617F testing, a discrepancy between exon 12 mutant allele burden in bone marrow and peripheral blood has occasionally been described.

High EPO level

A raised EPO level should lead to a thorough search for secondary causes of erythrocytosis, which may require additional supplementary investigations.

• CT head and neck
  -Cerebellar haemangioblastoma
  -Meningioma
  -Parathyroid carcinoma/adenoma
  
  
• consider further investigaion for secondary cause if clinically suspected
  -referral to respiratory/renal, sleep studies

Reference:

McMullin MF et al. Guidelines for the diagnosis, investigation and management of polycythaemia/erythrocytosis. Br J Haematol. 2005 Jul;130(2):174-95

McMullin MF et al. A guideline for the diagnosis and management of polycythaemia vera. A British Society for Haematology Guideline.British Journal of Haematology, 2019, 184, 176-191