In a patient with persistently elevated hematocrit and hemoglobin, negative JAK2 V617F and exon 12, MPL, and CALR mutations, normal bone marrow biopsy, no smoking, no respiratory symptoms, and no B symptoms, what is the next step in evaluation?

Evaluate for Secondary Causes of Erythrocytosis

In a patient with persistently elevated hematocrit and hemoglobin who is triple-negative for JAK2 (V617F and exon 12), MPL, and CALR mutations with a normal bone marrow biopsy, the next step is to measure serum erythropoietin (EPO) level to distinguish between primary and secondary erythrocytosis. 1

Diagnostic Algorithm

1. Measure Serum Erythropoietin Level

This is the critical next step that will guide your entire workup:

• Low or inappropriately normal EPO: Suggests an occult myeloproliferative neoplasm (MPN) despite negative molecular testing
• Elevated EPO: Points toward secondary erythrocytosis requiring further investigation

The NCCN guidelines explicitly include serum EPO level as part of the standard diagnostic workup for suspected MPN 1, and the 2007 WHO criteria revision identifies low serum EPO as a minor diagnostic criterion for polycythemia vera 2.

2. If EPO is Low or Inappropriately Normal

Consider these possibilities:

• JAK2-negative polycythemia vera: While rare (approximately 3% of PV cases are triple-negative 2), this exists and requires meeting additional WHO criteria
• Perform endogenous erythroid colony (EEC) assay: This is a minor diagnostic criterion that can help establish PV diagnosis when molecular testing is negative 2
• Re-evaluate bone marrow biopsy: Look specifically for panmyelosis with prominent erythroid and megakaryocytic proliferation, which is a minor criterion for PV 2

The 2007 WHO criteria specifically address your scenario: diagnosis can be made with the first major criterion (elevated hemoglobin/hematocrit) plus at least two minor criteria (bone marrow histology consistent with MPD, low EPO, and presence of EEC) when molecular testing is negative 2.

3. If EPO is Elevated

Systematically evaluate for secondary causes:

Hypoxia-related causes (even without respiratory symptoms):

• Arterial blood gas with oxygen saturation
• Sleep study for obstructive sleep apnea (common and often asymptomatic)
• High-altitude residence or recent travel
• Chronic lung disease (subclinical)
• Cardiac right-to-left shunt

Renal causes:

• Renal ultrasound to evaluate for cysts, hydronephrosis, or masses
• Renal cell carcinoma can produce EPO without other symptoms

Other tumors producing EPO:

• Hepatocellular carcinoma
• Cerebellar hemangioblastoma
• Uterine leiomyoma
• Pheochromocytoma

Congenital causes:

• High oxygen-affinity hemoglobin variants (requires specialized testing)
• Congenital EPO receptor mutations (rare, usually family history)
• Chuvash polycythemia (VHL gene mutation)

4. Additional Molecular Testing Considerations

Given the sensitivity limitations of standard testing 3, consider:

• Repeat JAK2 V617F testing with a more sensitive assay: The assay should detect mutant allele burden as low as 1-3% 3. Some patients have very low allele burdens that may be missed by less sensitive methods 4
• Broader NGS panel: Recent evidence suggests that broader sequencing panels may identify atypical mutations or rare JAK2 exon 14 mutations not captured by standard testing 5

Critical Pitfalls to Avoid

• Don't assume triple-negative status rules out MPN: Approximately 3% of PV cases are truly triple-negative 2, and very low allele burdens may be missed 4
• Don't overlook occult secondary causes: The absence of respiratory symptoms doesn't exclude sleep apnea or subclinical lung disease
• Don't dismiss the diagnosis without checking EPO: This single test fundamentally changes your diagnostic pathway
• Don't forget that "normal" bone marrow can still show subtle features: Have an experienced hematopathologist specifically look for MPD-consistent features

Quality of Life and Morbidity Considerations

Regardless of the underlying cause, persistent erythrocytosis increases thrombotic risk. While completing the workup:

• Consider therapeutic phlebotomy to maintain hematocrit <45% in men or <42% in women to reduce thrombotic complications
• Assess cardiovascular risk factors
• Evaluate for prior thrombotic events (even occult splanchnic vein thrombosis can occur with very low JAK2 allele burdens 4)

The EPO level is your next definitive step—it will either point you toward occult MPN requiring additional minor criteria for diagnosis or redirect you toward secondary causes that need systematic exclusion.