Mutational analysis for JAK2 V617F should be conducted. The patient presented with iron deficiency anemia and thrombocytosis. Thrombocytosis is often associated with iron deficiency anemia, particularly if bleeding is the cause of the anemia. However, when the patient's anemia was corrected with oral iron and oral contraceptive pills for better regulation of menstruation, thrombocytosis persisted, suggesting a disorder in platelet regulation. Iron deficiency is the most common cause of reactive thrombocytosis, which corrects within weeks of correcting the iron deficiency. Infection, inflammation, and malignancy are other causes. With iron deficiency ruled out as a cause and no other causes clinically apparent, essential thrombocythemia (ET) becomes more probable. Her lack of splenomegaly is fairly typical. The JAK2 activating mutation is present in 50% of patients with ET, so a negative result would not exclude the diagnosis, but a positive result supports the diagnosis of a myeloproliferative neoplasm (polycythemia vera, ET, or primary myelofibrosis).

BCR-ABL testing, then bone marrow aspiration and biopsy, would be performed if the platelet count remained persistently elevated after correction of serum iron levels with a negative JAK2 mutation status, because myeloproliferative neoplasms other than ET can less commonly elevate the platelet count. In ET, general hypercellularity and megakaryocyte hyperplasia would be seen on the bone marrow examination.

Testing the prothrombin and activated partial thromboplastin times would not be the most appropriate choice, because it focuses the diagnosis on a bleeding diathesis rather than thrombocytosis. Similarly, von Willebrand factor antigen testing does not address the patient's persistently elevated platelet count.