Erythrocytosis, or increased red blood cell mass, may be primary as in the case of polycythemia vera (PV), or secondary due to a variety of causes related to erythropoietin (EPO) secretion and hypoxia. Chronic pulmonary disease and certain EPO-secreting tumors should be addressed and excluded early during the course of evaluation for a patient presenting with increased red blood cell mass. Inclusion of the JAK2 V617F gene mutation in the recent World Health Organization criteria for the diagnosis of PV allows for facilitated diagnosis and guides therapy. EPO levels can be helpful in diagnosis and guiding therapy, but in the case of cystic renal diseases, EPO levels are often not elevated, creating diagnostic uncertainty. This report describes a case of symptoms directly attributable to erythrocytosis in the setting of negative JAK2 mutation and normal EPO levels. The subsequent discovery of a large cystic renal kidney and PV were the leading diagnostic considerations.
2016.