Red bone marrow is not a disease, but a state of the bone marrow. The bone marrow in our body is divided into red and yellow bone marrow. However, in a pathological state, some yellow bone marrow can be converted into red bone marrow. Red bone marrow is a kind of bone marrow with hematopoietic function in the body, which is a normal body tissue. Generally, young children have strong hematopoietic function, and all of their bone marrow cavities are filled with red bone marrow. After the age of 5 years, the red bone marrow in the long bones is gradually replaced by fat, and turns into yellow bone marrow. The average adult has about half red marrow and half yellow marrow. Red bone marrow is mainly found in the skull, sternum, ribs, vertebrae, clavicle and scapula. In old age, the body’s hematopoietic function decreases, fat gradually decreases, and the bone marrow will gradually change into mucous gelatinous bone marrow. Therefore, red bone marrow is generally normal and not a disease. However, diseases such as leukemia and myeloproliferative neoplasms may cause yellow bone marrow to turn into red bone marrow. If there are any uncomfortable symptoms, it is recommended to consult a doctor for effective treatment by a medical professional in conjunction with the test results.