Hematopathology | Pathology Student

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.

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Teardrop red cells

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Four similarities shared by all myeloproliferative disorders

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How to tell apart CML and benign neutrophilia

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How to tell apart CLL and benign lymphocytosis

Q. If you have a blood smear that shows a lymphocytosis, and all the lymphocytes look pretty mature, how do you know whether it’s chronic lymphocytic leukemia (CLL) or just a plain old benign lymphocytosis? (more…)

What does the bleeding time really measure?

Here’s a very good question about the diagnostic use of the bleeding time.

Q. I’m currently studying heme for boards and came across a practice questions that used platelet count, bleeding time, PT and PTT values to differentiate between certain diseases/problems. I was just wondering how in both Vitamin K deficiency and liver disease you can get an increase in PT and PTT but the bleeding time doesn’t change…I guess I figured that bleeding time would have to increase. Can you explain this to me?

A. Yeah, that does sound weird, you’d think the bleeding time would change – but actually, the bleeding time is only a measure of platelet function. It really has nothing to do with coagulation!

I kind of think of it like this: the platelet plug is the first thing to form, and that is enough to stop the bleeding from the incision made at the beginning of the test. The coagulation cascade happens next, and the status of that won’t be apparent in the bleeding time results. The patient might have some more bleeding later if their coagulation system is really screwed up…but the bleeding time assay will be done by then. In reality, it probably happens a little more concurrently than that (platelet plug is followed very closely by fibrin formation – the two probably even overlap a bit), but I think it’s a good way to remember the concept.

The same reasoning fits with the way that people with coagulation factor disorders bleed (as opposed to patients with platelet disorders). People with platelet abnormalities tend to bleed spontaneously into mucous membranes without much provocation (probably because they’re having a hard time forming that initial platelet plug) whereas patients with coagulation factor abnormalities, like hemophilia, tend to have deep, severe bleeds that happen after some time has elapsed (because they form the initial platelet plug okay, but they can’t seal it up with fibrin very well, so they end up bleeding later on).