[Diagnostic work-up of erythrocytosis]

Finding increased red cell indices - elevated RBC count, hemoglobin, or hematocrit (erythrocytosis) - is common in medicine. The key question is whether this reflects a myeloproliferative neoplasm (polycythemia vera, primary myelofibrosis, or essential thrombocythemia) driven by mutations such as JAK2, because it can cause thrombotic or hemorrhagic complications or progress to myeloid leukemia. We propose a diagnostic pathway for erythrocytosis that outlines the principal causes to exclude by targeted history and physical examination and incorporates the TRAKJAK score to predict JAK2 mutation positivity. By reducing unnecessary downstream testing, the score can lower costs and the environmental footprint of care.