Severe aplastic anemia (SAA)

It usually starts with a complete blood count (CBC), which counts red cells, white cells and platelets. In aplastic anemia, all three are usually low. The lab also counts young red cells (reticulocytes). A hematologist, a doctor who treats blood diseases, then usually arranges a bone marrow aspiration and biopsy. A needle takes a small sample of marrow, and the lab checks how many blood-making cells are left. Under the microscope, a marrow sample shows fewer blood-making cells than normal and more fat in their place.

Other tests look for conditions that can look the same. Flow cytometry, a test that sorts cells by markers on their surface, looks for cells linked to paroxysmal nocturnal hemoglobinuria (PNH). Chromosome and gene tests help rule out myelodysplastic disease and inherited marrow-failure conditions, such as Fanconi anemia or telomere disorders. Genetic results can take a few days to weeks.

The results also set the grade. Aplastic anemia is called severe when the marrow has less than a quarter of its normal cells. At least two counts must also be very low: neutrophils under 500, platelets under 20,000 or reticulocytes under 20,000 per microliter (under 60,000 when a machine does the count). It is very severe when neutrophils are under 200. The grade, along with age and donor options, guides treatment.

Immunosuppressive treatment commonly combines horse antithymocyte globulin, ciclosporin and eltrombopag. It aims to reduce the immune attack and help the remaining stem cells recover. Transfusions and infection prevention support the person while blood production improves.

An allogeneic transplant supplies blood-forming cells from another person. A matched sibling may be preferred; well-matched unrelated and other alternative donors are also options in appropriate settings. Guidance differs between countries. A 2024 US guideline from the American Society for Transplantation and Cellular Therapy looks at children and adults who have no matched relative. For them, it favors a transplant from a matched unrelated donor or a half-matched relative over immunosuppression. A 2024 UK guideline for adults lists immunosuppression or a transplant from a matched brother or sister as the first treatment. It keeps an unrelated-donor transplant mainly for when immunosuppression does not work, or for some young adults with severe infections who have a matched unrelated donor ready.

Age alone does not decide the treatment. Disease severity, active infection, other health conditions, donor availability, local guidance and the person’s preferences all matter. Recommendations for adults do not automatically apply to children.

When a transplant from a donor is planned, the team usually tests brothers and sisters first. Each full sibling has about a one in four chance of being a full match.

Most patients do not have a matched relative. In the words of NMDP, the U.S. registry, “75% of patients don’t have a fully matched donor in their own family.” The team then searches registries of volunteer donors around the world and banks of donated cord blood. In some transplants, a half-matched parent, child or sibling can also be the donor.

Matching depends on inherited tissue markers called HLA, so a patient is most likely to match someone who shares their ancestry. Every person who joins makes the search a little more likely to succeed, especially for patients from groups that are underrepresented on registries.

Most children and young adults with aplastic anemia are alive five years after diagnosis. Age is one of the strongest factors in outlook. Others include how severe the disease is and how soon treatment starts. For a transplant, the source of the cells matters too. In a large European study, survival was better when the transplant came within six months of diagnosis. It was also better when bone marrow was used rather than stem cells collected from the blood.

Medicine that calms the immune attack helps most people's counts improve. In an NIH study of 92 people who started treatment from 2012 to 2015 with eltrombopag added, most had better counts by six months, and 97% were alive about two years later. Counts can fall again, though. A 2018 expert review of long-term results says that after immune-calming treatment, about a third of people relapse or need long-term cyclosporine to keep their counts up. It also says about 15 in 100 develop a related marrow cancer, such as MDS or AML, in the ten years after treatment. That is why follow-up continues for years.

A donor transplant replaces the failing marrow and can cure it for some people. Younger people tend to do best. The numbers below describe groups of people treated years ago, and care has changed since. No number can say what will happen to one person.