Comparative studies of bone marrow from the United States and Japan.

Two hundred and eighty four bone marrow sections obtained at autopsy from the United States and 304 from Japan were evaluated. Patients who died of malignancy were excluded from the study. There was a significant increase in the incidence of lymphoid aggregates in the bone marrow with increasing age. After the age of 40, the incidence increased to 26.5 percent and 13.8 percent in the USA and Japan, respectively. After age 70, the frequencies reached 45.2 percent (USA) and 18.9 percent (Japan). There was a significant difference in the frequency of lymphoid aggregates between Americans and Japanese, and between females and males. The frequencies are 41.5 percent (females) and 35.1 percent (males) in the USA, and 18.7 percent (females) and 15.2 percent (males) in Japan. Bone marrow necrosis is more frequent in the old age group. The average frequency of marrow necrosis is 38 percent (USA) and 43.1 percent (Japan). Bone marrow fibrosis also increased with increasing age, reaching 16.1 percent (USA) and 19.5 percent (Japan) after the age of 70.