How to read a bone marrow biopsy

There are several things you should look for when evaluating a bone marrow biopsy specimen – see if you can see them in the image above.

First, take a look at the cellularity. The white spaces are fat cells that have washed out during processing; the cells in between the fat cells are hematopoietic precursors. The ratio of cells to fat is called the “cellularity.” The marrow above is approximately 30-40% cellular. You need to know the age of the patient to estimate whether the cellularity is normal. Here is a rough guide to cellularity by age:

0-3 months: 100%
3 months – 10 years: 80%
20 years: 65%
30 years: 50%
40 years: 45%
50 years: 40%
60 years: 35%
70 years and over: about 30%

Next, take a look at the composition of the marrow. Myeloid cells make up the largest percentage of the normal marrow cellularity; erythroid cells are second most common. The ratio of myeloid to erythroid cells should be about 2:1 to 4:1. It’s easier to see these cells on an aspirate smear, but you can get a pretty good idea on the marrow section too. Neutrophils and precursors often have eosinophilic, granular cytoplasm; if you look closely, you can see the indented nuclei of metamyelocytes and segmented nuclei of mature neutrophils. Erythroblasts generally have very round, dark nuclei; earlier forms are large, and later forms are small. A few megakaryocytes (large cells with abundant eosinophilic cytoplasm and multiple nuclei) should be sprinkled throughout the marrow too. Lymphocytes normally represent about 10-15% of the marrow cellularity. The above marrow appears to have a myeloid:erythroid ratio of 2:1, and megakaryocytes are normal in number.

Finally, take a look through all the sections to see if you see anything weird, like fibrosis, metastatic carcinoma, lymphoid aggregates, or amyloid deposition. As you scan the sections, you should see evenly-distributed cellularity, with evenly-spread hematopoietic precursors. Anything that deviates from this pattern should be investigated on higher power.

What do normal red blood cells look like?

Before you can really appreciate pathologic changes in red cells, you need to know what normal red cells look like.  Here is a normal blood smear image, taken at high power. (more…)