Idiopathic Erythrocytosis is More Common Than Polycythemia Vera in Indian Men
In Indian adult males with unexplained erythrocytosis, idiopathic erythrocytosis (IE) is substantially more common than polycythemia vera (PV), with IE accounting for approximately 80% of primary erythrocytosis cases. 1
Evidence from Indian Population
The most relevant and recent data from an Indian Armed Forces Hospital study demonstrates a clear predominance of IE over PV:
- IE represented 79.6% (39 of 49 patients) of primary erythrocytosis cases, while PV accounted for only 20.4% (10 of 49 patients) 1
- This 4:1 ratio of IE to PV is specific to the Indian population studied and represents the most direct answer to this question 1
- Among the PV cases identified, 7 had JAK2 V617F mutation, 1 had JAK2 Exon12 mutation, and 2 were JAK2-negative PV 1
Hemoglobin Thresholds and Diagnostic Implications
The distribution differs significantly based on hemoglobin levels:
- 90% of PV patients had hemoglobin >18.5 g/dL, compared to only 53.8% of IE patients (p=0.06) 1
- Notably, no JAK2-mutated patients had hemoglobin <18.5 g/dL 1
- Most patients with hemoglobin between 16.5-18.5 g/dL were classified as IE, suggesting that the revised WHO hemoglobin thresholds may be capturing a large proportion of IE cases 1
Clinical Distinguishing Features
When evaluating Indian men with erythrocytosis, key differentiating features include:
Laboratory parameters favoring PV over IE:
- Hemoglobin >18.5 g/dL strongly suggests PV 1
- Elevated white blood cell and platelet counts 2, 3
- Low serum erythropoietin levels 2, 3
- Red cell count >6.5 million/cmm 3
- Hematocrit ≥55% 3
Clinical features favoring PV:
- Splenomegaly (present in PV, absent in IE) 2, 3
- History of thrombotic events 2
- Older age at presentation 2
Features suggesting IE:
- Normal spleen size 2
- Normal platelet counts 2
- Higher serum EPO levels 2
- No history of thrombosis at diagnosis 2
Practical Diagnostic Approach
A functional test can help distinguish between these entities:
- Phlebotomy to achieve hematocrit <45% induces platelet count increase in 70% of PV patients but not in IE patients 2
- This response pattern can support the diagnosis of IE when other features are equivocal 2
Important Caveats
- The general epidemiology of PV shows a slight male preponderance (1.2:1) with median age at diagnosis of approximately 60 years 4
- However, this Indian cohort data specifically demonstrates that when evaluating primary erythrocytosis in Indian men, clinicians should have a higher index of suspicion for IE rather than PV 1
- Further genetic studies are needed to characterize the underlying causes of IE in the Indian population, as recent evidence suggests IE may be largely a germline disorder rather than a clonal hematopoietic condition 5