This patient requires CT of the abdomen and pelvis to detect possible renal cell carcinoma. The findings of a markedly elevated serum erythropoietin level due to secondary erythrocytosis plus vague midback pain and microscopic hematuria suggest the presence of an underlying renal cell carcinoma. Renal cell carcinoma is associated with secondary erythrocytosis in about 1% to 3% of patients. Polycythemia vera (PCV), a myeloproliferative neoplasm that results in excessive and unregulated erythrocyte production, is associated with very low serum erythropoietin levels. In contrast, an elevated serum erythropoietin level indicates the presence of secondary erythrocytosis. Although the most common causes of secondary erythrocytosis are chronic hypoxia and elevated carboxyhemoglobin concentrations due to tobacco use, an important cause is an erythropoietin-producing tumor. Other tumors commonly associated with secondary erythrocytosis include hepatocellular carcinoma and pheochromocytoma.

Bone marrow biopsy is not indicated because of this patient's markedly elevated serum erythropoietin level, which suggests external erythropoietin production and not a bone marrow disorder as a cause of this patient's polycythemia.

JAK2 mutation testing, which would be appropriate to rule out PCV in a patient with a very low serum erythropoietin level, is not indicated for this patient who has a markedly elevated level that is not compatible with a diagnosis of PCV.

Peripheral blood flow cytometry would not add useful information because this patient has isolated polycythemia and no evidence of abnormal lymphocytes. Flow cytometry is best used to help establish a diagnosis when evaluating for a malignancy that would reveal a monoclonal population of cells with a specific phenotype.