Bone marrow mitotic index: a methodological study

The mitotic index (MI) of bone marrow specimens is assessed in 3 different ways: method I determines the number of mitotic figures per 1,000 nucleated cells; method II counts the number of mitoses seen per 1,000 nucleated cells belonging to the proliferative pool, and method III is the same as method I, but excludes all lymphoid cells. 30 Giemsa-stained bone marrow smears from 6 children were screened by 3 independent investigators. MI of method II is found to be approximately twice as high as the MI of method I. The results of method III indicate that the size of the lymphoid population introduces a bias, which renders method I less reliable. It is concluded that method II is the method of choice for a reliable assessment of bone marrow MI.