What is the workup for erythrocytosis?

Workup for Erythrocytosis

Begin the diagnostic evaluation with JAK2 mutation testing (including exons 12-15) and serum erythropoietin (EPO) level to distinguish polycythemia vera from secondary causes. 1, 2

Initial Laboratory Assessment

First-Line Testing

• Complete blood count (CBC) with differential to confirm elevated hemoglobin/hematocrit and assess for associated thrombocytosis or leukocytosis 3
• JAK2V617F mutation testing (including exon 12 mutations) as the primary test to identify polycythemia vera, which accounts for >95% of clonal erythrocytosis 3, 1
• Serum erythropoietin level to differentiate clonal from secondary erythrocytosis—typically low or subnormal in PV (<70% sensitivity, >90% specificity) and normal-to-elevated in secondary causes 3, 1, 2

Hemoglobin/Hematocrit Thresholds

• Men: Hemoglobin >18.5 g/dL or hematocrit >55% warrants evaluation 3
• Women: Hemoglobin >16.5 g/dL or hematocrit >48% warrants evaluation 3
• Alternative criterion: Sustained increase of ≥2 g/dL from baseline, even if below absolute thresholds 3

Distinguishing Acquired vs. Congenital Erythrocytosis

Review Historical Data

• Longstanding erythrocytosis (present since childhood/young adulthood) suggests hereditary causes and requires germline mutation screening 2
• Acquired erythrocytosis (recent onset in adulthood) suggests PV or secondary causes 1, 2
• Family history of erythrocytosis strongly suggests hereditary etiology 2

Diagnostic Algorithm Based on JAK2 and EPO Results

JAK2 Mutation Positive + Low EPO

• Diagnosis: Polycythemia Vera 3, 1
• Confirm with bone marrow biopsy showing hypercellularity with trilineage growth (panmyelosis) if only one major criterion is met 3
• Diagnostic criteria require: Both major criteria (elevated Hgb/Hct AND JAK2 mutation) plus ≥1 minor criterion, OR first major criterion plus ≥2 minor criteria 3
• Minor criteria include: (1) bone marrow panmyelosis, (2) subnormal serum EPO, (3) endogenous erythroid colony formation 3

JAK2 Mutation Negative + Normal/Elevated EPO

Proceed to evaluate for secondary erythrocytosis 1, 2:

Assess for Hypoxia-Driven Causes

• Arterial oxygen saturation and arterial blood gas to identify central hypoxia 3, 2
• Chest radiograph to evaluate for cardiopulmonary disease 4
• Sleep study if obstructive sleep apnea suspected 2
• Smoking history and carboxyhemoglobin level for smokers 2
• High-altitude residence as physiologic cause 3, 2

Evaluate for EPO-Producing Conditions

• Renal imaging (ultrasound or CT) to identify renal cell carcinoma, renal cysts, or renal artery stenosis 2
• Abdominal imaging to detect hepatocellular carcinoma or other EPO-secreting tumors 2
• Medication review for testosterone, anabolic steroids, erythropoiesis-stimulating agents, or SGLT2 inhibitors 2

JAK2 Mutation Negative + Low EPO (Rare)

Consider hereditary erythrocytosis with germline mutation screening 1, 2:

Low EPO with Congenital Onset

• EPO receptor (EPOR) mutation testing—causes hypersensitivity to EPO (familial erythrocytosis type 1) 5, 2

Normal/Elevated EPO with Congenital Onset

Test for oxygen-sensing pathway defects 1, 6, 5:

• VHL gene mutations (familial erythrocytosis type 2) 6, 5
• EGLN1/PHD2 mutations (familial erythrocytosis type 3) 6, 5
• EPAS1/HIF2A mutations (familial erythrocytosis type 4) 6, 5
• EPO gene mutations (familial erythrocytosis type 5) 5

Evaluate for Increased Oxygen Affinity

• P50 measurement (oxygen tension at 50% hemoglobin saturation)—decreased P50 indicates high oxygen affinity 1, 2
• Hemoglobin electrophoresis and genetic testing for hemoglobin variants (HBB, HBA1, HBA2 mutations—familial erythrocytosis types 6-7) 5, 2
• 2,3-bisphosphoglycerate (2,3-BPG) level and BPGM gene testing (familial erythrocytosis type 8) 5, 2
• Methemoglobin level to exclude methemoglobinemia 2
• PIEZO1 mutation testing for rare hereditary xerocytosis with erythrocytosis 2

Additional Testing for Polycythemia Vera Confirmation

When JAK2 is Positive but Diagnosis Uncertain

• Bone marrow biopsy with histology showing characteristic hypercellularity, trilineage growth, and megakaryocyte clustering 3
• Cytogenetic studies may reveal abnormalities (trisomy 8 or 9, deletions of 13q or 20q) in 13-18% of cases, though not required for diagnosis 3
• Endogenous erythroid colony assay (if available) demonstrates spontaneous colony formation without EPO 3

Iron Status Assessment

• Serum ferritin and iron studies are essential, as iron deficiency can mask elevated hemoglobin in PV patients 3, 7, 8
• Microcytosis in the presence of thrombocytosis or leukocytosis suggests iron-deficient PV 3

Common Pitfalls to Avoid

• Do not measure red cell mass routinely—JAK2 mutation testing has replaced this cumbersome test in modern practice 1, 4
• Do not diagnose "idiopathic erythrocytosis" prematurely—this label often reflects incomplete evaluation and failure to account for normal population outliers 2
• Do not perform phlebotomy in non-clonal erythrocytosis without documented symptom benefit—cytoreductive therapy should be avoided in secondary and hereditary causes 2
• Do not overlook iron deficiency in suspected PV—formal diagnosis requires meeting hemoglobin/hematocrit criteria after iron repletion in research settings, though clinical diagnosis can proceed in practice 3
• Do not assume normal EPO excludes PV—up to 30% of PV patients have normal-range EPO levels 3
• Do not forget to assess for thrombotic risk factors—PV patients require cardiovascular risk optimization and consideration of low-dose aspirin 2

Special Clinical Scenarios

Borderline Hemoglobin with PV-Related Features

If hemoglobin/hematocrit is in the upper-normal range but patient has thrombocytosis, leukocytosis, splenomegaly, aquagenic pruritus, unusual thrombosis (Budd-Chiari syndrome), or erythromelalgia, proceed with full PV workup including JAK2 testing and bone marrow biopsy 3

Erythrocytosis with Thrombosis

Young patients with major thromboembolic events warrant urgent evaluation for HIF pathway mutations (VHL, PHD2, HIF2A), which can cause severe complications 6