People usually first notice acute biphenotypic leukemia when sudden, hard-to-explain symptoms appear over days to weeks, such as extreme fatigue, pale skin, frequent nosebleeds or bruising, fevers or infections that don’t clear, and sometimes bone pain or shortness of breath. A blood test done for these concerns often shows very low red cells and platelets with abnormal white cells, prompting urgent referral to a hematologist. Doctors then confirm the diagnosis with a bone marrow exam and specialized lab tests that show leukemia cells carrying features of both myeloid and lymphoid lines—the hallmark first signs of acute biphenotypic leukemia.