What is aplastic anaemia?

A blood condition that starts in the marrow, not the blood

Aplastic anaemia (spelled "anemia" in the US) is a rare, serious condition in which the bone marrow stops making enough blood cells. The name sounds like a milder cousin of the iron-deficiency anaemia many people have heard of, and it is nothing of the kind. The NHS inform guide is explicit that the two are different: aplastic anaemia is a serious bone marrow condition.

This page explains what the term means, how often it occurs, who tends to get it, what causes it and how it shows up in the body. It also covers how severity is graded, whether it counts as cancer, and what the outlook looks like in general terms. It is the starting point for the rest of the guide, so each section points onward to a fuller page.

Nothing here replaces the judgement of a haematology team, who can see your actual results. Think of this as the map, and your clinic as the people who know your particular road.

What aplastic anaemia actually is

Bone marrow is the soft tissue inside the bones where blood cells are made. In aplastic anaemia, production slows down or stops altogether, so there are not enough cells in the circulation. Three kinds are affected: red cells that carry oxygen, white cells that fight infection, and platelets that stop bleeding and bruising. If you want the full picture of how that factory normally runs, how bone marrow makes blood covers it step by step.

Doctors use two terms to describe what they find. Pancytopenia means all three blood cell counts are low at the same time. A hypocellular marrow means that when a sample of marrow is examined under the microscope, it holds far fewer blood-forming cells than it should. The British Society for Haematology guideline names pancytopenia with a hypocellular bone marrow as the defining feature, and notes that other conditions, including hypoplastic myelodysplastic syndromes, must be excluded first.

Some people hear "empty marrow" and picture a total void. The accurate picture is a marrow that is depleted of blood-forming cells, and how depleted varies from person to person.

How rare is it, and who gets it?

Very rare. NHS inform says it affects around 2 people in every 1 million each year in Scotland, and the US NIDDK gives almost the same figure for the United States, about 2 in every 1 million people diagnosed each year. The StatPearls review on aplastic anemia gives a wider range, 0.6 to 6.1 cases per million, and points out that the figure comes mainly from historical death registries. In other words, the true rate is hard to pin down, but it sits in the low single digits per million in Western countries.

It is not evenly spread around the world. The same StatPearls review notes that the occurrence of adult aplastic anaemia in Thailand and Taiwan exceeds that found in Western nations.

Anyone can be affected, and the sexes are affected about equally. Age is where things get interesting, because the condition tends to appear in waves rather than evenly across a lifetime. StatPearls describes two peaks, one in the first 30 years of life and a second in people over 60. NHS inform places the peaks at ages 10 to 20 and over 60, while NIDDK says it is more likely at ages 2 to 5, 20 to 25 and 55 and older. The sources slice the ages differently, but they agree on the broad shape: young people and older adults are over-represented, with a quieter stretch in between.

What causes it?

The most common mechanism is the immune system turning on the marrow. The US NHLBI describes the usual cause as an autoimmune process in which the immune system attacks the blood-forming stem cells. NHS inform calls it an unusual immune disorder for the same reason. Why the immune system misfires is usually unknown, which is why so many cases are labelled idiopathic. StatPearls puts the idiopathic group at 65 percent of cases.

When a trigger can be found, it tends to fall into a few groups.

• Medicines, including some chemotherapy drugs, and certain other prescription drugs (NIDDK mentions sulfonamides and some antiseizure medicines).
• Long-term exposure to chemicals such as benzene and pesticides.
• Infections, including viral infections and hepatitis. StatPearls says seronegative hepatitis accounts for roughly 5 to 10 percent of cases.
• Other autoimmune conditions, and pregnancy, which NIDDK lists among the risk factors.

A small number of cases are inherited. NHS inform names Fanconi anaemia, dyskeratosis congenita and Shwachman-Diamond syndrome as inherited conditions that can cause aplastic anaemia, and StatPearls reports telomerase defects in about 5 to 10 percent of adult-onset cases. These forms are more likely to be suspected in younger patients or when there is a family history, and a genetic test may be offered to rule them in or out. The difference between acquired and inherited marrow failure matters for treatment, so it has its own page: acquired versus inherited bone marrow failure.

One more point worth stating plainly. There is no way to prevent aplastic anaemia, according to NHLBI, and nothing a person did or did not do is likely to explain it. Many readers arrive carrying guilt about a past medicine, a workplace chemical or a virus. In most cases no link is ever proven.

Symptoms, cell line by cell line

The symptoms follow directly from which cells are in short supply. That makes them easier to understand than they first seem.

Low red cells

Red cells deliver oxygen, so a shortage brings fatigue, pallor, breathlessness and sometimes a fast heartbeat. NHS inform also lists headaches and chest pains. Tiredness is often the earliest and most easily dismissed sign, especially when it creeps in over weeks.

Low white cells

White cells defend against infection. When the neutrophils among them run low, fevers and bacterial infections become more likely, and severe neutropenia raises the risk of invasive fungal infections too, according to StatPearls. NHS inform describes recurring severe infections as a hallmark. A fever in someone known to have low counts is treated as urgent, and the guide on living with bone marrow failure covers practical precautions.

Low platelets

Platelets plug leaks in damaged blood vessels. A shortage shows up as easy bruising, tiny red or purple pinpoint spots on the skin called petechiae, and bleeding from the gums or nose. NHS inform lists bleeding and bruising among the main symptoms.

Not everyone feels unwell. StatPearls notes that some cases are found by chance, when a routine blood test shows abnormal counts. NHS inform adds that some people report brain fog and poor concentration, which may come from the condition, its treatment or other factors. If you are searching for early signs of aplastic anaemia, the honest answer is that they are vague: tiredness, bruises that seem out of proportion, and infections that will not clear. None of these points to aplastic anaemia alone, since far more common problems cause them, which is why a blood count is the sensible first step. How the diagnosis is then confirmed is set out in diagnosing bone marrow failure.

Non-severe, severe and very severe

Haematologists grade the condition by how low the blood counts have fallen. NHS inform describes three categories, not severe, severe and very severe, and explains that the fewer blood cells there are, the more severe the aplastic anaemia is likely to be. The BSH guideline refers to the Camitta criteria for this grading.

In everyday terms, a non-severe case means the counts are reduced but not dangerously so, and some people are watched closely rather than treated straight away. A severe case means the counts have dropped further, and very severe sits beyond that. NHS inform also warns that a low white cell count raises the risk of severe infection and a low platelet count raises the risk of bruising and bleeding. The exact cut-off numbers are set out in the clinical guidelines and your own team will tell you which category applies.

Grade matters because it shapes the plan. According to NHS inform, treatment depends on how severe the condition is, together with age, general health and any underlying conditions. The options are laid out in the aplastic anaemia treatment overview.

Is it cancer? Is it like leukaemia?

No. NHS inform states that aplastic anaemia is not a blood cancer. In leukaemia, abnormal cells multiply out of control. In aplastic anaemia the problem runs the other way: too few cells are being made, and the ones that do appear are healthy. NIDDK describes it as a condition in which many blood stem cells are injured or destroyed, yet the cells that are produced are normal.

The confusion is understandable, because some of the care looks alike. NHS inform notes that patients may be treated in hospital, need transfusions or a bone marrow transplant, and may have to take infection precautions similar to those used during chemotherapy.

There are links worth knowing about, though. NHLBI says aplastic anaemia can raise the risk of complications including leukaemia or other serious blood conditions, and NIDDK notes a higher risk of acute myeloid leukaemia in people with aplastic anaemia and especially in those with myelodysplastic syndromes (MDS), another bone marrow failure disorder in which the cells that are made do not work properly. NHS inform also says aplastic anaemia can sometimes be associated with paroxysmal nocturnal haemoglobinuria. That relationship is explained on the PNH page. These overlaps are one reason follow-up appointments continue after counts improve.

What the outlook looks like in general terms

The picture today is far more hopeful than many newly diagnosed readers fear. StatPearls reports survival of 80 to 90 percent in severe aplastic anaemia with modern treatment, and describes overall survival with transplant and immunosuppressive therapy as exceeding 80 to 85 percent. Younger age and higher reticulocyte and lymphocyte counts at diagnosis predict better outcomes.

Can it be cured? NHLBI says blood and bone marrow transplants may cure aplastic anaemia in some people, and other treatments can bring blood counts up without removing the underlying cause. Relapse is a real possibility. StatPearls says it occurs in up to one third of patients with severe aplastic anaemia, though a second course of immunosuppressive therapy works in 55 to 60 percent of them.

Those are averages gathered across large groups, and an average is not a forecast for one person. Age, severity, donor availability, other health problems and how early treatment starts all move the odds. The question of how long someone is likely to live is therefore one only the treating team can answer for a specific case.

Where to read next

If you have just had a diagnosis, the next useful steps are understanding how the tests work and what the treatment choices are. Start with diagnosing bone marrow failure for the blood counts and marrow biopsy, then aplastic anaemia treatment for the options. The questions of ongoing daily life, from fatigue to infection precautions, are handled in living with bone marrow failure.

Some readers will want to look further into related areas later, such as psychological support or the experience of children and young people with the condition. Those topics deserve their own space and will be added to the guide over time.

The short version: rare, serious, and far more treatable than it once was

Aplastic anaemia is a failure of the marrow to produce blood cells, usually because the immune system has attacked the stem cells that make them. It is not cancer, it is not preventable, and it is rarely anyone's fault. The symptoms trace back to low red cells, white cells and platelets, severity is graded by how far the counts have fallen, and survival figures with modern treatment are encouraging. A haematology team can tell you where you or your family member sits within that picture.