General information:
The assessment of bone marrow cellularity is semi-quantitative, i.e. the average estimate is performed at at 100-fold magnification. A 5-stage classification is used.
- empty bone marrow (aplastic bone marrow)
- decreased cellularity (hypocellular bone marrow)
- normal cellularity (normocellular bone marrow)
- increased cellularity (hypercellular bone marrow)
- full marrow (packed marrow)
Some hematologists consider the latter two to be equivalent.
Assessment:
The ratio of blood-forming cells to fat tissue (through fixation of detached "lacunae") is usually 1 to 1 for a middle-aged adult. Younger patients normally have higher cellularity, while older patients have lower cellularity. This corresponds to a normocellular bone marrow. If there is a hypocellular bone marrow, the blood-forming cells are clearly decreased, but still detected. In the case of an aplastic bone marrow, only a few blood-forming cells can be found. The remaining elements containing a nucleus are stromal cells. This picture is often observed, for example, in aplastic anemia or after myelosuppressive chemotherapy. The blood-forming marrow predominates in a hypercellular bone marrow. Fat lacunae can still be detected. In a packed marrow, no more fat lacunae are present and the entire marrow is filled with hematopoietic cells. This picture is typical of the acute leukemias and some myeloproliferative syndromes (e.g. in chronic myelocytic leukemia).
Note:
Ideally, bone marrow cellularity is assessed with a bone marrow biopsy.