Polycythemia Causes and Diagnostic Approach

Introduction to Polycythemia

Polycythemia results from either apparent (relative) causes due to plasma volume depletion, primary clonal disorders (polycythemia vera), or secondary causes driven by hypoxia-dependent or hypoxia-independent mechanisms 1, 2, 3

Plasma volume depletion from severe dehydration, diarrhea, vomiting, diuretic use, capillary leak syndrome, or severe burns causes relative polycythemia that is clinically obvious and does not require specialized testing 1, 2, 3
Smoker's polycythemia is a real condition caused by chronic carbon monoxide exposure, which binds hemoglobin with 200-250 times greater affinity than oxygen, creating functional hypoxia; this resolves with smoking cessation 1, 4, 5

Polycythemia vera (PV) is a JAK2-mutated myeloproliferative neoplasm with clonal erythrocytosis, characterized by low or inappropriately normal serum EPO levels 4
JAK2 V617F mutation is present in up to 97% of PV cases and should be tested when EPO is low or normal 4, 5
Bone marrow examination showing characteristic morphologic features remains the cornerstone for confirming PV diagnosis 4

Chronic lung disease (COPD, pulmonary fibrosis) triggers compensatory erythropoiesis through tissue hypoxia 1, 6, 7, 4
Right-to-left cardiopulmonary vascular shunts cause secondary polycythemia due to hypoxia 1, 6, 7, 4
High-altitude habitation leads to physiologic polycythemia as an adaptive response to reduced atmospheric oxygen 1, 6, 7, 4
Carbon monoxide poisoning and chronic exposure in smokers creates functional hypoxia 1, 6, 7
Hypoventilation syndromes including obstructive sleep apnea cause chronic intermittent hypoxia leading to compensatory erythrocytosis 1, 6, 7, 4, 8

Step 1: Distinguish apparent from true polycythemia by assessing for clinically obvious plasma volume depletion and verifying hemoglobin/hematocrit values are truly elevated beyond sex- and race-adjusted normal values 1, 2, 3, 9, 5
Step 2: Measure serum EPO level as the key discriminator; low or inappropriately normal EPO suggests polycythemia vera, while elevated EPO suggests secondary polycythemia 4, 5
Step 3: Evaluate for hypoxia if EPO is elevated, using arterial blood gas analysis or pulse oximetry, and chest X-ray to evaluate for chronic lung disease 5
Step 4: If EPO elevated without hypoxia, evaluate for tumors using abdominal ultrasound or CT to screen for renal cell carcinoma, hepatocellular carcinoma, or other EPO-producing tumors 5
Step 5: Consider congenital causes in young patients, including hemoglobin electrophoresis for high oxygen-affinity hemoglobinopathy and genetic testing for EPOR mutations, von Hippel-Lindau gene mutations, or 2,3-DPG mutase deficiency 1

The American Society of Hematology classifies polycythemia vera (PV) as a chronic myeloproliferative disorder along with essential thrombocythemia and myelofibrosis with myeloid metaplasia, representing clonal stem cell disorders 10, 11
PV often presents with leukocytosis, thrombocytosis, and panmyeloid hyperplasia of the bone marrow, with risks of progression to myelofibrosis or acute leukemia 10