What is the most consistent laboratory finding in a patient suspected of having polycythemia vera?

In a patient suspected of having polycythemia vera, a low serum erythropoietin (EPO) level is indeed the most consistent laboratory finding. Polycythemia vera is a myeloproliferative neoplasm characterized by the overproduction of red blood cells, often associated with a mutation in the JAK2 gene. This overproduction occurs independently of erythropoietin levels.

When polycythemia vera is present, the body does not require increased EPO levels to stimulate erythrocyte production. Consequently, individuals with this condition typically have low serum EPO levels, which helps differentiate it from secondary causes of erythrocytosis, where EPO levels are generally high due to stimuli such as chronic hypoxia or tumors producing ectopic EPO. Therefore, a low serum EPO level is a key marker that supports the diagnosis of polycythemia vera in clinical practice.