History and examination should assess

• Recent travel and residence at high altitude (>3000m).

• COAD, other hypoxic respiratory conditions, cyanotic congenital heart disease, other cardiac problems causing hypoxia.

• Smoking—heavy cigarette smoking causes 4 carboxyHb levels leading to 4 RBC mass to compensate for loss of O2 carrying capacity.

• Ventilatory impairment 2° to gross obesity, alveolar hypoventilation (Pickwickian syndrome).

• Possibility of high-affinity Hb abnormalities arises if there is a FH of polycythaemia, otherwise requires assessment through Hb analysis.

• If obvious secondary causes excluded possibilities include:

Spurious polycythaemia—pseudopolycythaemia or Gaisbock's syndrome, associated features can include cigarette smoking, obesity, hypertension and excess alcohol consumption; sometimes described as 'stress polycythaemia'.

Primary proliferative polycythaemia (polycythaemia rubra vera) —

plethoric facies, history of pruritus after bathing or on change of environmental temperature and presence of splenomegaly are helpful clinical findings to suggest this diagnosis.

Inappropriate erythropoietin excess—occurs in a variety of benign and malignant renal disorders. Rare complication of some tumours including hepatoma, uterine fibroids and cerebellar haemangioblastoma.

Part of clinical assessment must also include an evaluation of thrombotic risk; previous thrombosis or a family history of such problems increase the urgency of investigation and appropriate treatment m p240-249.

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