The causes of aplastic anemia fall into two groups. In acquired aplastic anemia, the most common form, the patient’s own T cells attack the blood-forming stem cells. This is sometimes triggered by a drug, a toxin or hepatitis, but most often no trigger is found. In inherited aplastic anemia, a gene defect such as Fanconi anemia weakens the stem cells from birth. In both cases, the bone marrow becomes empty and cannot make enough red cells, white cells or platelets.
Finding the cause is not just an academic exercise. It decides which tests we order, whether family members need screening, and whether immunosuppression or a transplant is the better first treatment. Below I go through each cause and the newer insights that have changed care.
What Is Aplastic Anemia?
Aplastic anemia is a hematologic disorder defined by pancytopenia (low counts of all three blood cell lines) together with a hypocellular marrow. On biopsy, most of the marrow space is replaced by fat, and there are no abnormal cells infiltrating it. The problem is too few stem cells, not a cancer crowding them out.
Every circulating cell comes from these stem cells, which sit in the marrow cavities of the skeletal system’s blood-forming tissue. When they fail, all cell lines fall together. This is what separates aplastic anemia from a simple anemia. For background on other anemias, see our anemia guide.
Acquired Causes of Aplastic Anemia
Immune-mediated (idiopathic) aplastic anemia
In most patients, no outside trigger is ever identified. We now understand that these “idiopathic” cases are mostly immune-mediated. Activated cytotoxic T cells release inhibitory signals, especially interferon-gamma, and destroy the stem cell pool. The strongest evidence is that most patients recover blood counts after immunosuppressive treatment.
Drugs
Drugs damage the marrow in two ways. Predictable, dose-related suppression follows chemotherapy and radiation, and it usually recovers. Idiosyncratic reactions are rare and unpredictable. They have been linked to chloramphenicol, some anticonvulsants such as carbamazepine and felbamate, gold salts, and certain sulfonamides and anti-thyroid drugs. Only a tiny fraction of people who take these drugs are affected.
Toxins and radiation
Long-term exposure to benzene is the classic chemical cause. It matters mainly in industrial settings. High-dose ionizing radiation causes marrow failure that depends on the dose received.
Viral infections
Hepatitis-associated aplastic anemia usually follows an acute hepatitis that tests negative for all known hepatitis viruses. It tends to appear weeks to months after the liver inflammation, most often in young males. Epstein-Barr virus and HIV are less common links. Parvovirus B19 typically stops only red cell production (pure red cell aplasia), not all three lines.
Other associations
Aplastic anemia can rarely appear during pregnancy or with autoimmune conditions. It is closely linked to paroxysmal nocturnal hemoglobinuria (PNH). Many patients carry small PNH clones, and a few go on to develop clinical PNH.
Inherited Bone Marrow Failure Syndromes
Inherited forms matter most in children and young adults. They also affect how we treat the patient and whether a sibling can be a donor. More detail is in our article on pediatric aplastic anemia.
| Syndrome | Underlying defect | Clues |
|---|---|---|
| Fanconi anemia | Faulty DNA repair | Short stature, thumb and forearm anomalies, skin pigment changes; positive chromosome breakage test |
| Dyskeratosis congenita and other telomere disorders | Telomeres that shorten too quickly | Abnormal nails, white mouth patches, lacy skin pigmentation, lung or liver scarring |
| Shwachman-Diamond syndrome | Ribosome assembly | Pancreatic insufficiency, poor growth, low neutrophils |
| GATA2 deficiency | Blood-forming transcription factor | Unusual infections, low monocytes, lymphedema |
A telomere disorder can first appear in adulthood with no physical signs. That is why testing for these syndromes is part of a modern work-up in younger adults, not only in children.
How Doctors Work Out the Cause
The work-up has two goals: confirm marrow failure and rule out conditions that look like it. Typical steps include:
- Complete blood count and reticulocyte count: confirm pancytopenia with a low reticulocyte response.
- Bone marrow biopsy with cytogenetics: shows low cellularity and helps separate aplastic anemia from hypoplastic myelodysplastic syndrome, which is the most important condition to rule out.
- PNH flow cytometry: looks for PNH clones.
- Inherited-syndrome screening: chromosome breakage testing, telomere length measurement and gene panels when the history or age suggests them.
- Liver tests, viral serology, B12 and folate: identify hepatitis-associated cases and nutritional causes that can be reversed.
Severity is graded from the counts. Severe aplastic anemia means a marrow cellularity below about 25% plus at least two of the following: neutrophils below 500 per microliter, platelets below 20,000 per microliter, or a very low reticulocyte count. Very severe disease means the same criteria with neutrophils below 200 per microliter.
Treatment: How the Cause Shapes the Plan
Hematopoietic stem cell transplantation from a matched sibling is the preferred first treatment for many younger patients with severe disease, and it can be curative. In inherited syndromes, transplant needs gentler conditioning regimens, and a sibling donor must first be tested to confirm they do not carry the same condition.
For older patients, or those without a matched donor, immunosuppressive therapy is standard. It combines antithymocyte globulin (ATG) and cyclosporine, now commonly with eltrombopag, a drug that stimulates the thrombopoietin receptor. Adding eltrombopag was a major advance and has improved response rates. It works because acquired disease is driven by the immune system. Immunosuppression does not help inherited marrow failure.
While waiting for a response, supportive care keeps patients safe. This includes red blood cell transfusions and platelet transfusions, prompt treatment of fever, antimicrobial prophylaxis and management of iron overload. For a wider view of blood health, see our hematology guide.
When to See a Doctor
Seek medical review promptly if you notice unusual tiredness together with easy bruising, pinpoint red spots on the skin (petechiae), bleeding gums, or repeated or severe infections. A fever in someone known to have low neutrophils is an emergency. A simple blood count is the first step and can be arranged quickly.
Frequently Asked Questions
Is aplastic anemia a type of cancer?
No. Aplastic anemia is marrow failure, not a malignancy, and the marrow is empty rather than filled with abnormal cells. A minority of patients later develop myelodysplastic syndrome or leukemia, which is why long-term follow-up continues after recovery.
Can a medication I took have caused my aplastic anemia?
It is possible but uncommon. Your hematologist will review every medicine you took in the months before diagnosis and stop any suspected drug. Most cases turn out to be immune-mediated with no identifiable trigger.
Can aplastic anemia be passed on to my children?
Acquired aplastic anemia is not inherited. The inherited syndromes, such as Fanconi anemia and telomere disorders, can be passed on. Genetic counseling is recommended when one of them is diagnosed.
Can aplastic anemia be cured?
Stem cell transplantation can cure it, and immunosuppressive therapy produces lasting responses in many patients with acquired disease. Relapse can happen after immunosuppression, so blood counts are monitored for years.
