How aplastic anaemia is diagnosed

Why one blood test is never enough

A low blood count is usually the first clue, and it cannot settle the question alone. Many conditions can lower red cells, white cells and platelets together, so diagnosis has two jobs. The team has to show that the marrow itself is failing, and they have to rule out conditions that look similar.

This page follows that process roughly in the order it happens. It covers routine blood tests, the work done to exclude other causes, the bone marrow sample, genetic checks, and how severity is graded. Centres differ in the details. If you want the condition itself explained first, the what aplastic anaemia is page covers that.

Starting with the blood count and the blood film

The full blood count, usually called the CBC, measures red cells, white cells and platelets. It also reports haemoglobin, the protein that carries oxygen around the body. In aplastic anaemia all three cell lines are typically low, a pattern known as pancytopenia. Great Ormond Street Hospital explains that GPs or local paediatricians usually order blood tests first, and that the full blood count may show the marrow is not making enough healthy cells.

A blood film, where a sample is spread on a slide and examined under a microscope, adds detail. The reticulocyte count matters here too. Reticulocytes are young red cells that have just left the marrow, so a low number suggests the marrow is not keeping up. In the StatPearls review of aplastic anemia, a reticulocyte count below 1 per cent is one of the cytopenia findings used in the diagnostic criteria.

A low count is not proof on its own. The GOSH page notes that early symptoms and results can be confused with leukaemia, which is why the next stages matter.

Ruling out look-alike conditions

Several conditions can resemble aplastic anaemia. The most important to exclude is hypoplastic myelodysplastic syndrome, in which the marrow is sparse but abnormal. The British Society for Haematology adult guideline states that the diagnosis is confirmed only after this and other alternatives have been excluded.

Flow cytometry is one of the tools used. It tags blood cells with markers so they can be counted and sorted by type. According to the StatPearls review, it helps separate hypoplastic MDS from aplastic anaemia and looks for PNH. Clinicians also take a careful history, asking about recent viral illnesses, medicines, toxins and radiation. Hepatitis, Epstein-Barr virus, parvovirus B19 and COVID-19 are among the infections that come up. Vitamin B12 and folate levels are usually checked as well, since deficiency can also pull the counts down. The paroxysmal nocturnal haemoglobinuria page explains why the PNH test matters.

The bone marrow sample

A bone marrow sample is the only method that diagnoses aplastic anaemia with certainty, as GOSH puts it, because the problem sits in the marrow and the team needs to see it directly. If the marrow’s normal job is unclear, the how bone marrow makes blood page explains what the team is looking at.

Dana-Farber describes the procedure. A local anaesthetic numbs the back of the hip, a needle draws a liquid aspirate, and a small core of bone and marrow is taken through the same site. That core is what is often called a trephine biopsy. The skin and bone surface are numbed first, so the main sensation is usually pressure and pulling rather than a sharp pain. Some soreness afterwards is normal. Ask your team what pain relief they use and whether a sedative is an option at your centre.

Results arrive in stages. The aspirate often produces a “dry tap”, meaning little liquid comes back, which is one reason the core matters. NCBI describes the typical finding as a hypocellular marrow with fatty replacement and no fibrosis or malignant infiltration. The lab also runs extra stains and tests on the same material, so the full answer can take longer than the first look. Ask what timeline to expect for your own tests.

Cytogenetics and screening for inherited causes

Cytogenetics examines the chromosomes in marrow cells. In aplastic anaemia the karyotype is typically normal. When a sample yields few cells, FISH or SNP arrays can still give useful information. A next-generation sequencing panel can also look for mutations such as DNMT3A and ASXL1.

Inherited bone marrow failure is considered too, because it changes treatment choices and family advice. Telomere length and chromosome breakage tests can help rule it out. Germline testing on a blood or skin sample checks for known or suspected inherited mutations, and Dana-Farber notes that relatives may be offered testing as well. Doctors also look for physical features such as short stature, abnormal thumbs, heart defects and skin or nail changes. In children, GOSH notes that Fanconi anaemia is the commonest inherited cause. The acquired versus inherited page sets out the main groups.

The table below summarises what each test looks for.

How severity is graded

Once the diagnosis is confirmed, the team grades severity. The BSH guideline says the Camitta criteria are used for this, and that severity, age and the availability of a matched donor all shape treatment decisions. Grading matters because it helps decide between immunosuppressive treatment and transplant.

Great Ormond Street’s summary, which is written for children, grades disease by looking at neutrophils, platelets and how active the marrow is. The neutrophil count is the main dividing line: below 0.5 x 10⁹ per litre points to severe disease and below 0.2 x 10⁹ per litre to very severe disease, alongside a platelet count below 20 x 10⁹ per litre and marrow activity below 30 per cent. Results that fall short of those patterns are classed as non-severe, and in practice doctors weigh the measures together rather than reading off one number. Adult grading can differ in detail and centres may use slightly different versions, so ask your team which scale they are applying.

Being told you have a rare condition can be hard, and the emotional side of a first diagnosis is easy to overlook in clinical summaries. Many people find it useful to write down questions between appointments and to bring someone along to the next one.

A diagnosis built from many small answers

No single number confirms aplastic anaemia. The blood counts point toward marrow failure, the exclusion tests close off look-alikes, the marrow sample shows the problem directly, and the genetic checks look for an inherited cause. When your team explains a result, it is usually one piece of a larger picture. Asking how each test fits into that picture is one of the most useful things you can bring to an appointment, and the questions to ask your haematologist page offers a starting list.