Hematology-Oncology Q50

Answer & Critique

Correct Answer: B

Educational Objective: Diagnose polycythemia vera.

Key Point

JAK2 V617F mutation is present in 97% of patients with polycythemia vera, so testing should be performed in patients in whom the disease is suspected.

The most appropriate diagnostic test to perform is for the JAK2 V617F mutation. Polycythemia vera (PV) is a disorder of the myeloid and erythroid stem cells that causes erythropoietin-independent proliferation of erythrocytes. This older adult patient has an elevated hematocrit level, a low erythropoietin level, and splenomegaly, indicating a likely diagnosis of PV. More than 97% of patients with PV have the JAK2 mutation. The 2016 World Health Organization major criteria for PV include increased hemoglobin level (>16.5 g/dL [165 g/L] in men and >16 g/dL [160 g/L] in women), a bone marrow biopsy specimen showing hypercellularity and increased reticulin and collagen fibrosis, and positive findings for JAK2 or exon 12 mutation. JAK2 mutation testing can be done on peripheral blood granulocytes.

Calreticulin mutation has been recently found in JAK2-negative myeloproliferative disorders such as essential thrombocythemia and myelofibrosis. Evaluation for the calreticulin mutation would not be indicated in the absence of thrombocytosis or cytopenia.

Translocation of chromosomes 9 and 22, resulting in a BCR-ABL fusion gene, is seen in patients with chronic myeloid leukemia (CML). CML can present with elevated leukocyte and platelet counts, but polycythemia is not a typical presentation.

Most causes of secondary erythrocytosis share the mechanism of an elevated erythropoietin level, which is most commonly driven by hypoxemia. Polycythemia can be the presenting symptom of undiagnosed sleep apnea, and all patients with polycythemia should be screened for symptoms and signs of sleep apnea. However, in this patient with no symptoms, a low erythropoietin level, and splenomegaly, PV is much more likely, and JAK2 mutational analysis should be performed first.

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