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Diagnosis and tests

How to read a bone marrow report

A bone marrow report is often a long document full of terms: cellularity, myelogram, blast percentage, fibrosis, immunohistochemistry. This topic calmly explains which parts such a report contains, what each part means and which questions are useful to ask your doctor.

Last updated: ~5 min read
A folded translucent glowing document slowly unfolding on a dark navy background; each layer lights up a different image — marrow tissue, cells, coloured dots and chromosomes; no writing.
Figure 1.Concept: a marrow report is a map that unfolds layer by layer.

01Short answer

A bone marrow report usually has several parts: a description of the sample (the aspirate — the liquid part — and the trephine biopsy — a small core of bone), sample quality (adequate or not), cellularity (what percentage of the marrow is filled with blood-forming cells), the differential or myelogram (the percentage of each cell type), the blast percentage, dysplasia (abnormally shaped cells), fibrosis (fibrous tissue), an iron stain and immunohistochemistry (staining of markers such as CD34 and CD117 in the tissue). Flow cytometry, cytogenetic and molecular results are given in separate sections or separate reports. The most important part is the final diagnosis or comment at the end. At diagnosis, the blast percentage helps define the type of leukemia; after treatment, fewer than 5% blasts in the marrow together with recovered blood counts are key criteria for complete remission, and an MRD test measures an even deeper response.

02Simple explanation

Read the report from the end: the final diagnosis or comment sums up all the details briefly.

Cellularity shows how “full” the marrow is. In leukemia it is often overfull; after chemotherapy it may be temporarily empty.

The blast percentage is the share of immature cells. In healthy marrow it is usually under 5%. In acute leukemia it is much higher.

The myelogram is a list of cell types — neutrophil precursors, red cell precursors, lymphocytes and so on. For the doctor it is a detailed map.

Flow cytometry, chromosome and gene results often come separately and later. The full picture appears only when they are all together.

03Scientific explanation

Aspirate and trephine biopsy. According to MedlinePlus, aspiration removes the liquid part of the marrow and biopsy removes a small core of tissue. The aspirate shows cell shapes and percentages well (the myelogram); the biopsy shows the marrow’s structure, cellularity and fibrosis. When no aspirate can be drawn (a “dry tap”) — for example with fibrosis or a packed marrow — the biopsy is especially important.

Cellularity and age. Normal cellularity falls with age: in children the marrow is almost completely filled with cells, while in older people it may be less than half. Pathologists describe it as “normal for age, increased or decreased”. The ratio of myeloid to erythroid cells (M:E ratio) is also recorded.

Blasts and classification. Under the 2022 WHO classification, the general threshold for AML is at least 20% blasts in the marrow or blood (fewer is enough with certain genetic changes). Fewer blasts may point to other diagnoses, such as a myelodysplastic syndrome. Immunohistochemistry (for example CD34, CD117, TdT, CD20, CD3) shows where blasts and lymphoid cells sit within the tissue.

After treatment. The traditional criteria for complete remission are fewer than 5% blasts in the marrow, no blasts in the blood and recovered blood counts. According to ELN recommendations, MRD testing in AML (by flow cytometry or a molecular test) assesses a deeper response. A “hypocellular marrow” after treatment can be an expected, temporary state.

04What happens in the body?

How the report is organised

The header gives your name, the date and where the sample was taken from (usually the hip bone). Then come the gross description, the microscopic description, additional tests and the final diagnosis. Some hospitals bring all results together in one “integrated” report.

Cellularity: how full is the marrow?

This shows what percentage of the marrow is made of blood-forming cells and what percentage is fat. At diagnosis of leukemia the marrow is often packed; after chemotherapy it empties temporarily and then gradually recovers.

Two translucent bone cross-sections side by side on a dark navy background: on the left the marrow spaces are densely packed with glowing cells; on the right the cells are sparse with pale fat spaces between them.
Figure 2.Cellularity: a full marrow and an emptied marrow.

Blast percentage and the myelogram

The specialist counts hundreds of cells and records the percentage of each type. The blast percentage is the number people notice most: at diagnosis it helps define the type of leukemia, and after treatment it helps assess the response. Always read it together with the date and the stage of treatment.

Under a magnifying lens on a dark navy background, a mix of blood cells among which a few large violet blasts with big nuclei are picked out by soft light; no numbers or labels.
Figure 3.Blast percentage: the share of immature cells.

Fibrosis, iron and dysplasia

Fibrosis is the amount of fibrous tissue (usually graded from 0 to 3). The iron stain shows iron stores. Dysplasia means abnormally shaped cells and matters for some diagnoses. These terms can sound alarming — ask your doctor what they mean for you.

Discussing the result with your doctor

Useful questions: “What does the final conclusion say?”, “Is this blast percentage what you expected?”, “Which results are we still waiting for?”, “Does this change the treatment plan?”, “When is the next marrow test?”. Keep a copy of the report.

05Reading a marrow report: four steps

From the overall picture to the detail.

Conclusion — Read the final section first.1ConclusionRead the final section first.
Cellularity — How full is the marrow?2CellularityHow full is the marrow?
Blasts — The percentage of immature cells.3BlastsThe percentage of immature cells.
Extra tests — Flow, chromosomes, genes — separately.4Extra testsFlow, chromosomes, genes — separately.
A readable documentThe terms no longer frighten.
Precise questionsA productive talk with your doctor.
The trendComparison with earlier marrow tests.

06Common phrases in a bone marrow report

PhraseMeaningNote
Hypercellular marrowMore cells than normalCommon in leukemia at diagnosis
Hypocellular marrowFew cellsCan be temporary after chemotherapy
Blasts: under 5%Few immature cellsOne of the criteria for remission
Blasts: 20% or moreMany immature cellsGeneral threshold for AML (WHO 2022)
M:E ratioRatio of myeloid to erythroid cellsShows the balance of blood formation
Reticulin fibrosis MF-0 to MF-3Grade of fibrous tissueAt high grades an aspirate is hard to obtain
Inadequate sampleToo little material to assessA repeat test may be needed

* Thresholds and terms can depend on the type of leukemia, the classification system and the laboratory. Discuss what your report means with your hematologist.

07Key terms

Aspirate
The liquid part of the marrow drawn with a needle.
Trephine biopsy
Removal of a small core of bone and marrow.
Cellularity
The percentage of the marrow filled with blood-forming cells.
Myelogram
The percentage breakdown of cell types in the marrow.
Blast
An immature blood cell.
Dysplasia
Abnormal shape and development of cells.
Fibrosis
An increase in fibrous (scar-like) tissue in the marrow.
Immunohistochemistry
Showing markers in tissue with special stains.
Complete remission
No signs of leukemia found by standard tests.

08Key points

  • Start reading the report from the final section.
  • Cellularity shows how full the marrow is and depends on age.
  • The blast percentage matters for diagnosis and for judging response.
  • In remission, marrow blasts are usually under 5%.
  • Flow, chromosome and gene results often come separately and later.
  • An “inadequate sample” sometimes means repeating the test.
  • Always interpret the numbers together with your doctor.

09Frequently asked questions

My report says “hypercellular”. Is that bad?

It means the marrow contains more cells than normal. This is common in leukemia at diagnosis, but it can have other causes too. Your doctor will explain what it means together with the final diagnosis.

After treatment the report says the marrow is “empty”. Should I worry?

After chemotherapy the marrow can be temporarily empty — this is expected. Recovery takes several weeks. Your doctor follows it with blood counts and, if needed, a repeat marrow test.

Two reports give different blast percentages. Why?

Marrow can differ slightly from one spot to another, the aspirate and biopsy can give different numbers, and microscopy and flow cytometry are different methods. Your doctor weighs all the information together.

Why are the genetic results not in the report?

Because they are done in a different laboratory and take longer. They arrive as a separate report or as an addendum later.

Can I get a copy of the report and the slides?

At many hospitals, yes. For a second opinion, both the report and the glass slides or tissue blocks are useful. Ask your doctor how to arrange this.

10Questions for your doctor

Take these questions to your appointment. The ones you save are collected on the “My questions” page and stay on this device only.

  1. My report says “hypercellular”. Is that bad?

  2. After treatment the report says the marrow is “empty”. Should I worry?

  3. Two reports give different blast percentages. Why?

  4. Why are the genetic results not in the report?

  5. Can I get a copy of the report and the slides?

My questions

12Sources

  1. MedlinePlus (U.S. National Library of Medicine). Bone Marrow Tests
  2. MedlinePlus (U.S. National Library of Medicine). Bone marrow aspiration
  3. MedlinePlus (U.S. National Library of Medicine). Bone marrow biopsy
  4. National Cancer Institute (NCI). Surgical Pathology Reports
  5. American Cancer Society. Understanding Your Pathology Report
  6. American Cancer Society. Tests for Acute Myeloid Leukemia (AML)
  7. Cancer Research UK. Bone marrow test
  8. Macmillan Cancer Support. Bone marrow biopsy
  9. National Cancer Institute (NCI). NCI Dictionary of Cancer Terms: blast
  10. National Cancer Institute (NCI). NCI Dictionary of Cancer Terms: minimal residual disease
  11. Leukemia (journal), 2022. Khoury JD et al. The 5th edition of the WHO Classification of Haematolymphoid Tumours: Myeloid and Histiocytic/Dendritic Neoplasms
  12. Blood (American Society of Hematology), 2021. 2021 Update on MRD in acute myeloid leukemia: a consensus document from the European LeukemiaNet MRD Working Party
Medical disclaimerThis information is for educational purposes only and does not replace medical advice.
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