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Understanding your report

Reading Your — Bone Marrow Biopsy Report

A bone marrow biopsy report is written in the language of pathology, not the language of patients. The numbers and words are real and important — and understanding what they describe helps you have a better conversation with your haematologist.

Medically reviewed by Dr. Mohammed Imaduddin, Surgical Oncologist, MBBS · MS (General Surgery) · M.Ch (Surgical Oncology) · Last reviewed September 2026

  • Cellularity is a ratio — It tells you how much of your marrow space is filled with blood-forming cells versus fat — and normal looks different at every age.
  • Blasts are immature cells — A small number is always present in healthy marrow. The percentage in the report is a key figure your haematologist will focus on.
  • No single number stands alone — Every figure in the report is read alongside your blood counts, symptoms, and clinical history — not in isolation.
  • Results go to your haematologist first — They review everything together before explaining what it means for your diagnosis and next steps.
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Cellularity describes how full your bone marrow is with blood-forming cells, expressed as a percentage. A high number means the marrow is more active than expected for your age; a low number means less active. Neither tells the whole story without your blast percentage and blood test results alongside it.

What does cellularity mean in a bone marrow report?

Cellularity is the proportion of the marrow cavity occupied by blood-forming cells rather than fat. Young marrow is naturally denser; older marrow normally contains more fat. So a figure that looks low for a twenty-year-old may be entirely normal for a seventy-year-old.

When your report says hypercellular, the marrow is more packed than expected for your age. Hypocellular means less packed. Neither word is a diagnosis — both are descriptions that your haematologist reads in the context of the full report.

The number on its own tells you almost nothing. Your age, your blood counts, the blast percentage, and what the individual cells look like under the microscope are what give it meaning.

How do I read through a bone marrow biopsy report?

  1. Start with the final impression or conclusion

    This is usually the last section, and it summarises what the pathologist found. Read it first so you know where the rest of the report is heading before you look at any numbers.

  2. Find the cellularity figure

    Look for a percentage or the words hypercellular or hypocellular. Note it, but do not try to interpret it without everything else.

  3. Find the blast percentage

    Blasts are immature cells. The report states what proportion of the cells counted were blasts. This is one of the most important figures, and your haematologist will explain what it means for your situation.

  4. Look at the cell differential

    This section lists proportions of different cell types found in the sample. You do not need to interpret each line — it is read as a pattern, and the pathologist's conclusion reflects all of it together.

  5. Note any comments on cell appearance or fibrosis

    The pathologist may describe how individual cells look — whether their shape or size is abnormal — and whether there is scarring in the marrow. These observations feed into the overall picture.

  6. Bring the printed report to your appointment

    Write your questions in the margins. Ask your haematologist to walk you through the conclusion. Having the document in front of both of you makes the conversation more specific.

What are blasts, and why does the percentage matter?

Blasts are the earliest, most immature form of blood cells. Healthy marrow always contains a small proportion of them — they are a normal part of how blood is made.

When the blast percentage rises above what is expected, it can signal that the marrow is not maturing cells properly. How far above normal, and what else is present in the report, determines the significance. Your haematologist uses WHO classification criteria to interpret this against your full clinical picture.

The blast count is a measurement, not a verdict. Your haematologist will explain what it means for your diagnosis and what happens next.

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What questions should I ask my haematologist about the report?

  • What does my cellularity figure mean for someone my age?
  • What is my blast percentage, and is it within or outside the normal range?
  • Were the cells described as normal in appearance, or was dysplasia noted?
  • Is there any fibrosis, and if so, how much?
  • What did the aspirate and the trephine each show — did they agree?
  • What are the next steps based on these findings?

What does my haematologist do with the biopsy result?

The report does not reach you as a standalone answer. Your haematologist reviews it alongside your full blood count, any previous biopsies, scan results, and your symptoms. The combination is what guides the diagnosis and any treatment recommendation.

Some reports return with a clear finding. Others are inconclusive, and a repeat biopsy or additional testing may follow. An inconclusive result is not a failure of the procedure — it is an honest answer when the picture is not yet complete.

If you have received the report before seeing your haematologist, do not try to interpret the numbers alone. Write down what you do not understand and bring those questions to your appointment.

What do the terms in my bone marrow report mean?

Cellularity

The percentage of the marrow cavity filled with blood-forming cells rather than fat. It is interpreted against your age, because what is normal changes across a lifetime. A number that appears low in a young adult may be appropriate in an older patient, which is why the pathologist always states whether it is normal, hypocellular, or hypercellular for your age group — not just what the figure is.

Blast percentage

The proportion of cells in the sample that are blasts — immature cells that have not yet developed into functional red cells, white cells, or platelets. A small number of blasts is normal in healthy marrow. When the percentage is raised, its significance depends on how high it is, which cell lines are involved, and what else the report shows. Your haematologist uses WHO classification criteria to interpret the figure in the context of your full clinical picture.

Aspirate and trephine

A standard bone marrow biopsy collects two samples at the same time. The aspirate is a liquid sample drawn from the marrow space that allows individual cells to be spread on a slide and counted in detail. The trephine is a small solid core of bone and marrow that preserves the architecture — how cells are arranged and how dense the marrow is. They give complementary information, and a complete report addresses both.

Dysplasia

A description of cells that look abnormal under the microscope — the wrong size, shape, or internal structure compared to what is expected. The pathologist notes which cell types show dysplasia and to what degree. It is an observation that contributes to the overall interpretation, not a diagnosis by itself. Its significance depends on how many cell lines are affected and what the blast percentage shows alongside it.

Hypercellular and hypocellular

Hypercellular means the marrow is more densely packed with blood-forming cells than is normal for your age. Hypocellular means less densely packed than expected. Both terms describe the landscape the pathologist is examining. Both can be features of several different conditions, and neither is a diagnosis on its own — they are part of the picture your haematologist assembles from the full report.

Fibrosis or reticulin

The marrow contains a fine supporting network of fibres called reticulin. The pathologist grades the amount present, typically on a numbered scale. When fibrosis is increased beyond a normal level, it can affect how the marrow functions and may be associated with certain conditions. Your haematologist will explain whether the grade recorded in your report is relevant to your diagnosis and whether it changes what treatment is recommended.

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Common questions

Frequently asked questions

My report says my cellularity is low. Does that mean my marrow is failing?

Not necessarily. Hypocellular marrow has several possible causes — some serious, some not. It can reflect a condition affecting the marrow, but it can also be a feature of normal ageing, a medication effect, or recovery after treatment. Your haematologist will interpret the figure alongside your blood counts and clinical history before drawing any conclusion. A description of density is not the same as a diagnosis of failure.

The blast percentage in my report worries me. What level is dangerous?

The level that is clinically significant depends on your specific diagnosis and the classification framework your haematologist is using. Searching for a threshold online and comparing it to your own number is likely to produce more anxiety than clarity, because the same percentage means different things in different clinical contexts. Ask your haematologist directly: what does this percentage mean for my situation, and what does it tell us about next steps? That question will get you a more useful answer than any figure in a general source.

Why does my report mention two different samples — aspirate and trephine?

These are the two components of a standard bone marrow biopsy, usually collected during the same procedure. The aspirate is a liquid sample that lets the laboratory count and examine individual cells in fine detail. The trephine is a small solid core that shows how the marrow is organised overall — how dense it is and how the cells are arranged. Each gives information the other cannot, and reading both together gives a more complete picture than either alone.

My report mentions dysplasia. Should I be alarmed?

Dysplasia means the pathologist has seen cells that look abnormal in shape, size or internal appearance under the microscope. It is an observation, not a diagnosis by itself. Dysplasia in one cell type has a different significance from dysplasia affecting several, and what it means depends on the blast percentage and other findings in the same report. Your haematologist will explain whether the dysplasia noted is relevant to your overall clinical picture and what, if anything, follows from it.

I received the report before my appointment. Should I read it now?

Yes, if you want to — and many patients find it useful to be familiar with the terms before they sit down with their haematologist. The most productive approach is to note down the words and numbers you do not understand rather than trying to interpret them yourself. Bring those questions to your appointment. A printed copy with your questions written in the margins helps you get through the conversation efficiently, and it means you leave with specific answers rather than general reassurance.

How long does a bone marrow biopsy result take?

Processing a bone marrow biopsy takes longer than a blood test because the solid trephine sample must go through a chemical processing step before it can be examined under the microscope. Most results are available within one to two weeks of the procedure, though samples sent for specialist testing or complex cases may take longer. Your haematologist's team will give you an expected timeline when the biopsy is done. If you have not heard back within that timeframe, it is entirely reasonable to call and ask.

Full index

Browse all 701 biopsy topics

Every page in this section, grouped by the part of the journey it belongs to. Pick a group to see what is in it.

What Is a Biopsy?

What Is a Biopsy? Everything You Need to Know →

Types of Biopsy Compared

Which Biopsy Will You Have? Techniques Compared →

Preparing for a Biopsy

What to Expect on the Day of Your Biopsy →

Recovery and Aftercare

After a Biopsy: Recovery, Aftercare and Warning Signs →

Biopsy by Body Part

Biopsy by Body Part: What to Expect at Each Site →

Understanding Your Report

How to Read a Biopsy Report: Terms Explained →

IHC and Molecular Markers

IHC and Molecular Markers on a Biopsy: What They Mean →

Grading and Scoring Systems

Cytology & Prostate Scoring Systems Explained →

How Accurate Is a Biopsy?

How Accurate Is a Biopsy? Errors and Second Opinions →

If Your Result Is Benign

Your Biopsy Is Benign: What It Means and What Comes Next →

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