At a center for hematological malignancy molecular diagnostics that receives greater than 2000 JAK2 V617F diagnostic tests per annum, 24 requests for JAK2 V617F mutation status were identified with clinical details provided of RCC (disease stage unknown) and either erythrocytosis and/or raised hemoglobin and/or raised hematocrit from January 2006 to December 2022 inclusive. Here, JAK2 is linked to polycythemia.