Polycythaemia
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Direct answer
Polycythaemia is an elevated red-cell mass — or, in relative (spurious) polycythaemia, a normal red-cell mass concentrated by reduced plasma volume (dehydration, diuretics, alcohol, "stress polycythaemia") — presenting with hyperviscosity symptoms: headache, dizziness, tinnitus, visual blurring, burning palms and soles (erythromelalgia), and thrombosis including Budd-Chiari syndrome in the young. Absolute polycythaemia divides into primary — polycythaemia vera, a myeloproliferative neoplasm in which a JAK2 V617F mutation (over 95 percent) drives autonomous erythropoiesis with suppressed erythropoietin — and secondary, with appropriately raised erythropoietin from chronic hypoxia (altitude, chronic lung disease, cyanotic heart disease, sleep apnoea, smoking) or erythropoietin-secreting tumours (renal cell, hepatocellular, cerebellar haemangioblastoma). Treatment of polycythaemia vera is phlebotomy to a haematocrit below 45 percent, with low-dose aspirin and cytoreduction (hydroxycarbamide) for high-risk patients.
What you must remember
- Classification in one breath: relative (low plasma volume, normal red-cell mass — dehydration, diuretics, alcohol) versus absolute: primary polycythaemia vera with JAK2 and LOW erythropoietin; secondary with HIGH erythropoietin from hypoxia or tumour — the erythropoietin level is the fork.
- Polycythaemia vera clinical set: hyperviscosity symptoms, erythromelalgia (burning palms and soles, responsive to aspirin), aquagenic pruritus (itching after hot baths — histamine), gout from high cell turnover, splenomegaly, and thrombosis including hepatic vein (Budd-Chiari) — polycythaemia vera belongs in every young Budd-Chiari work-up.
- Laboratory discriminants: haemoglobin over 16.5 g/dL in men (16.0 in women, WHO 2016) or raised haematocrit, JAK2 V617F positivity in over 95 percent (exon 12 in most of the rest), LOW erythropoietin, often leucocytosis, thrombocytosis and basophilia.
- Treatment targets and doses: venesection 400-500 mL every few days initially, maintaining haematocrit BELOW 45 percent (42 considered for women in some guidance); low-dose aspirin 75-100 mg daily; hydroxycarbamide for high-risk patients (age over 60 or prior thrombosis), interferon-alpha preferred in young or pregnant patients.
- Secondary polycythaemia causes: chronic hypoxia — altitude (a real Indian entity in Ladakh), chronic obstructive pulmonary disease, sleep apnoea, cyanotic congenital heart disease; smoking; erythropoietin-secreting tumours — renal cell, hepatocellular, cerebellar haemangioblastoma, uterine fibroma; post-transplant erythrocytosis; exogenous erythropoietin and androgens.
- Physiological adaptation: high-altitude residents may carry haematocrits that would be disease at sea level — treat symptoms, not numbers; phlebotomy is reserved for symptomatic hyperviscosity.
- Complication clock of untreated vera: thrombosis early, and over years transformation to myelofibrosis (post-polycythaemic myelofibrosis) or acute myeloid leukaemia — the reason for lifelong haematological follow-up.
- Emergency picture: hyperviscosity with thrombosis or visual loss warrants urgent phlebotomy (with volume replacement) — and remember that repeated venesection can deplete iron stores, with iron replacement used cautiously (it drives erythropoiesis), with iron replacement used cautiously (it drives erythropoiesis).
Working through a high haemoglobin
A 54-year-old man presents with three months of headache, itching after hot showers and burning feet; haemoglobin 19 g/dL, haematocrit 57 percent, white cells 13,000 with basophilia, platelets 620,000, and a palpable spleen tip. The constellation of leucocytosis, thrombocytosis and basophilia shouts myeloproliferative neoplasm rather than a relative rise: JAK2 V617F is positive and erythropoietin low — polycythaemia vera. Management opens with venesection 450 mL twice weekly until haematocrit is under 45 percent, daily aspirin 75 mg, allopurinol for hyperuricaemia, and risk stratification — his age puts him in the high-risk group, so hydroxycarbamide is added; he is counselled on transformation risk and lifelong surveillance.
The contrasting pathway belongs to a 46-year-old mountain-dwelling smoker with chronic lung disease, haemoglobin 18.5 g/dL, normal white cells and platelets, JAK2 negative and erythropoietin high — secondary polycythaemia, managed by treating the lungs and stopping smoking, with phlebotomy only for hyperviscosity symptoms. The third archetype is the anxious executive on diuretics with haemoglobin 17 but a normal red-cell mass — relative polycythaemia, needing reassurance and hydration, not venesection. Three haematocrits, three diseases, separated by erythropoietin, JAK2 and red-cell mass.
Where students slip
The recurring slip is treating every high haemoglobin as one disease: the exam's architecture is the three-way split (relative, primary, secondary), bridged by the erythropoietin level plus JAK2 status. Second, the target number: below 45 percent is the trial-supported phlebotomy goal, and "normal range" is not the answer. Third, aquagenic pruritus and erythromelalgia are the two symptoms a generic summary underweights and NBE overtests; erythromelalgia responding to aspirin is stem-worthy. Fourth, Budd-Chiari in a young patient puts polycythaemia vera on the screen-first list. Fifth, physiological secondary polycythaemia at altitude is not routinely venesected — only symptomatic hyperviscosity justifies it. Finally, transformation to myelofibrosis or acute leukaemia supplies the follow-up questions.
Frequently asked questions
How is polycythaemia classified?
Relative (reduced plasma volume, normal red-cell mass), primary absolute (polycythaemia vera with JAK2 mutation and low erythropoietin), and secondary absolute (high erythropoietin from hypoxia or tumours).
What is the haematocrit target in polycythaemia vera and why?
Below 45 percent, achieved by venesection, because controlled follow-up showed thrombosis rates rise significantly above this threshold.
Which mutation and laboratory pattern confirm polycythaemia vera?
JAK2 V617F (over 95 percent, exon-12 variants in most others) with low serum erythropoietin, often with leucocytosis, thrombocytosis and basophilia.
What is erythromelalgia in this context?
Burning pain and redness of palms and soles from platelet-mediated microvascular occlusion, characteristically relieved by low-dose aspirin.
When is phlebotomy indicated in secondary polycythaemia?
Only for symptomatic hyperviscosity (headache, visual disturbance, thrombosis) in secondary or physiological polycythaemia; otherwise treat the underlying hypoxic cause.