Aplastic Anemia: Understanding Your Pathology Report

Section Editor: David Li MD
July 5, 2026

Aplastic anemia is a condition in which the bone marrow, the soft tissue inside bones where blood cells are made, fails to produce enough new blood cells. The word “aplastic” refers to the loss of blood-cell production, and, as a result, the marrow becomes hypocellular, meaning it contains far fewer blood-forming cells than normal. Because all three main types of blood cells are affected, people with aplastic anemia usually have low levels of red blood cells, white blood cells, and platelets at the same time, a combination called pancytopenia. Aplastic anemia is not a cancer, but because other bone marrow conditions can look similar, careful testing is needed to confirm the diagnosis.

This article will help you understand the findings in your pathology report and blood test results for aplastic anemia, what each term means, and why it matters for your care.

What are the symptoms of aplastic anemia?

The symptoms of aplastic anemia come from having too few of each type of blood cell. Because each cell type has a different job, the symptoms fall into three groups:

Low red blood cells (anemia) — Fatigue, weakness, shortness of breath, and pale skin.
Low white blood cells (neutropenia) — Frequent or severe infections, because the body has fewer neutrophils to fight germs.
Low platelets (thrombocytopenia) — Easy bruising, bleeding gums, nosebleeds, or small red spots on the skin.

What causes aplastic anemia?

In most cases, aplastic anemia develops when the body’s own immune system mistakenly attacks and destroys the blood-forming stem cells in the bone marrow. This is called acquired immune-mediated aplastic anemia, and no specific trigger is often found. When a cause is identified, it may include:

Medications and toxins — Certain drugs, or exposure to chemicals such as benzene.
Radiation — High-dose radiation exposure.
Viral infections — Some viral infections, including certain types of hepatitis.
Inherited bone marrow failure syndromes — Rare genetic conditions, such as Fanconi anemia and dyskeratosis congenita, that can cause the marrow to fail. These are more often considered in children and younger adults, and they are important to identify because they change treatment.

How is the diagnosis made?

The diagnosis of aplastic anemia begins with blood tests and is confirmed with a bone marrow examination, after other causes of low blood counts have been ruled out. A complete blood count (CBC) typically shows pancytopenia, meaning low counts of red blood cells, white blood cells, and platelets. A related test measures reticulocytes, which are newly made red blood cells; in aplastic anemia, the reticulocyte count is low, showing that the marrow is not producing enough new cells. A blood smear, a thin layer of blood examined under the microscope, usually shows reduced numbers of cells that otherwise look normal, without the abnormal or immature cells that would point to a different condition.

A bone marrow biopsy and aspiration are needed to confirm the diagnosis. A pathologist examines the samples and looks for a markedly hypocellular marrow, described in more detail in the next section. Because a low blood count with an empty-looking marrow can have several causes, aplastic anemia is considered a diagnosis of exclusion, and additional tests are performed to rule out other conditions. These often include cytogenetic testing (which examines the chromosomes and is usually normal in aplastic anemia), flow cytometry to evaluate a related condition called paroxysmal nocturnal hemoglobinuria, and, particularly in younger patients, genetic testing to evaluate for an inherited bone marrow failure syndrome.

What does aplastic anemia look like under the microscope?

The defining feature of aplastic anemia on the bone marrow report is a hypocellular marrow. Instead of being filled with the many developing blood cells that normally crowd a healthy marrow, the marrow space is largely replaced by fat, with only scattered blood-forming cells remaining. Just as important is what the pathologist does not see: there is no increase in immature cells called blasts, no abnormal or unusually shaped cells (a feature called dysplasia), no scarring (fibrosis), and no infiltration by cancer cells. This combination of an empty marrow without these other changes is what separates aplastic anemia from conditions such as myelodysplastic syndrome or leukemia, which can also cause low blood counts but show additional abnormal findings.

How is the severity of aplastic anemia determined?

Doctors classify aplastic anemia by severity, because this guides how urgently and how intensively it is treated. The severity is based on how low the blood counts are, using the reticulocyte count, the neutrophil count, and the platelet count, together with the degree of marrow hypocellularity:

Non-severe aplastic anemia — Blood counts are reduced but do not reach the thresholds for severe disease.
Severe aplastic anemia — The marrow is markedly hypocellular and at least two of the three blood counts (neutrophils, platelets, and reticulocytes) are very low.
Very severe aplastic anemia — The same as severe disease, but with an even lower neutrophil count, which increases the risk of serious infection.

What happens after a diagnosis of aplastic anemia?

After aplastic anemia is diagnosed, treatment is guided by the severity of the disease, the person’s age, and whether a suitable stem cell donor is available. The findings on the blood and bone marrow reports help shape several decisions:

Supportive care — Blood and platelet transfusions, along with prevention and prompt treatment of infections, are important throughout the course of the disease.
Immunosuppressive therapy — Because the immune system is often the cause, medicines that calm it, such as antithymocyte globulin (ATG) and cyclosporine, are a primary treatment. A medication called eltrombopag, which helps stimulate blood cell production, is now commonly added to improve the response.
Stem cell (bone marrow) transplant — An allogeneic transplant, using blood-forming cells from a donor, can cure aplastic anemia and is often the preferred treatment for younger patients with severe disease who have a matched donor.

Care is provided by a hematology team, and regular blood tests and follow-up help track the response to treatment. Over time, a small number of people develop a related bone marrow condition, such as myelodysplastic syndrome or paroxysmal nocturnal hemoglobinuria, so ongoing monitoring is important. Decisions about treatment are made by the care team together with the patient, based on the specific findings in the report.

What is the prognosis for aplastic anemia?

The outlook for aplastic anemia has improved greatly with modern treatment. Severe aplastic anemia can be life-threatening if untreated, mainly because of the risks of serious infection and bleeding, but most people respond well to immunosuppressive therapy or a stem cell transplant, and many are cured or have long-term control of the disease. Because there is a small long-term risk of developing another bone marrow condition, long-term follow-up is recommended. Your prognosis depends on your own combination of these factors, which your care team can explain in the context of your specific report.

Questions to ask your doctor

What did my blood counts and bone marrow biopsy show?
How hypocellular was my bone marrow?
Is my aplastic anemia non-severe, severe, or very severe?
Were other causes of low blood counts, such as myelodysplastic syndrome, ruled out?
Do I need testing for paroxysmal nocturnal hemoglobinuria or an inherited bone marrow failure syndrome?
Is my aplastic anemia likely immune-related, or was another cause found?
What treatment is recommended for my situation?
Am I a candidate for immunosuppressive therapy, a stem cell transplant, or both?
What can be done to lower my risk of infection and bleeding in the meantime?
What long-term follow-up will I need?
Are there clinical trials that I should consider?