Diagnosis and tests

Symptom → test → diagnosis

The path from the first suspicion to an exact diagnosis has several steps. This topic shows, in order, which test is done at each step and why it is needed.

Last updated: 14 October 2026~3 min read

Four glowing steps on a dark navy background with a feather, a test tube, a microscope and a DNA helix. — **Figure 1.**Four steps from symptom to diagnosis.

01Short answer

The path to a diagnosis usually runs: symptoms or an abnormal routine test → full blood count and blood smear → hematologist review → bone marrow aspiration and biopsy → immunophenotyping (flow cytometry) → cytogenetic and molecular tests. The blood count raises suspicion, and blasts may be seen on the smear. The bone marrow test shows the percentage of blasts. Flow cytometry uses “markers” on the cell surface to identify the type of leukemia (myeloid or lymphoid, B or T). Genetic tests (karyotype, FISH, PCR, NGS) define the subtype and risk. Blood chemistry, clotting tests and, when needed, a spinal fluid test and heart check are also done.

02Simple explanation

Step one: a full blood count. Red cells, white cells and platelets are counted. If anything is abnormal, a blood smear is looked at under a microscope.

Step two: the bone marrow. A thin needle takes liquid marrow (aspiration) and a tiny piece of tissue (biopsy) from the hip bone, under local anaesthetic.

Step three: the cell’s “passport”. Flow cytometry shows which family the leukemia cells belong to.

Step four: genetics. Changes in chromosomes and genes are looked for. These define the subtype and the treatment plan.

03Scientific explanation

Blast threshold: according to the ACS, AML is usually diagnosed when at least 20% of cells in the marrow or blood are blasts; but with certain genetic changes, such as t(8;21), inv(16) or t(15;17), AML is diagnosed even with fewer blasts.

Immunophenotyping: according to MedlinePlus, flow cytometry tags cells with special antibodies and counts them with a laser. This separates AML from ALL and B-ALL from T-ALL, and lays the groundwork for later tracking of measurable residual disease (MRD).

Genetic tests: a karyotype looks at all chromosomes, FISH quickly finds specific changes, and PCR and NGS detect gene changes such as FLT3, NPM1 and BCR-ABL1. According to the NCI, these results define the risk group and the choice of targeted drugs.

04What happens in the body?

How is a bone marrow test done?

Usually lying down, from the back of the hip bone. The skin and bone surface are numbed, and sometimes a sedative is offered. It takes 15–30 minutes. There may be mild soreness for a day or two.

A marrow sample and a flow cytometer in a calm lab, a teal beam passing through a thin stream of cells. — **Figure 2.**Flow cytometry reads the “passport” of leukemia cells.

When are results ready?

A blood count takes hours; a marrow smear and flow cytometry take one or two days. A karyotype and some molecular tests can take one to three weeks.

Glowing chromosomes arranged in pairs on a dark background, one pair highlighted in gold. — **Figure 3.**Genetic tests define the subtype.

Additional tests

Liver and kidney function, electrolytes, uric acid, clotting tests, infection tests, a heart ultrasound (before some drugs) and, in ALL, a spinal fluid test.

05The four steps of diagnosis

Each step answers the next question.

1SymptomSomething has changed.

2Blood testSuspicion arises.

3Bone marrowLeukemia confirmed.

4GeneticsSubtype and risk.

TypeMyeloid or lymphoid.

SubtypeGenetic changes.

PlanChoice of treatment.

06Tests and the questions they answer

Test	What does it show?	When is it ready?
Full blood count	Cell numbers	Hours
Blood smear	Whether blasts are present	1 day
Bone marrow aspiration/biopsy	Blast percentage, marrow structure	1–5 days
Flow cytometry	Type of leukemia (AML/ALL, B/T)	1–2 days
Karyotype, FISH	Chromosome changes	FISH: days; karyotype: 1–3 weeks
PCR / NGS	Gene mutations (FLT3, NPM1, etc.)	Days to 2–3 weeks

* Timings vary between laboratories.

07Key terms

Aspiration: Taking the liquid part of the bone marrow.
Biopsy: Taking a tiny piece of tissue.
Flow cytometry: Analysing cells by the markers on their surface.
Karyotype: A microscope study of all the chromosomes.
FISH: A test that finds specific gene changes with glowing probes.
NGS: A test that reads many genes at once.

08Key points

Diagnosis is made step by step.
A blood test raises suspicion; the marrow confirms it.
Flow cytometry identifies the type.
Genetics shows the subtype and risk.
Some results take weeks.
The treatment plan rests on all the results.

09Frequently asked questions

Is a bone marrow test very painful?

With local anaesthetic most people feel pressure and brief pain. Mention your worries beforehand; a sedative may be offered.

Why does treatment start before all results are back?

In acute leukemia, delay can be dangerous. Core treatment begins, and the plan is refined when the genetic results arrive.

Will the test be repeated?

Yes, the marrow test is repeated at set stages to check the response to treatment.

Can I get copies of my results?

Yes, and it is worth keeping them: they help with second opinions and future care.

10Questions for your doctor

Take these questions to your appointment. The ones you save are collected on the “My questions” page and stay on this device only.

Is a bone marrow test very painful?
Why does treatment start before all results are back?
Will the test be repeated?
Can I get copies of my results?

My questions

12Sources

American Cancer Society. Tests for Acute Myeloid Leukemia (AML)
National Cancer Institute (NCI). Adult Acute Myeloid Leukemia Treatment (PDQ) – Patient Version
NHS. Acute myeloid leukaemia: Diagnosis
MedlinePlus. Bone marrow biopsy
MedlinePlus. Flow cytometry
Leukemia & Lymphoma Society. Diagnosing leukemia
British Journal of Haematology, 2020. The revised guidelines for the diagnosis and management of hairy cell leukaemia and the hairy cell leukaemia variant
Annals of Oncology (ESMO), 2015. Hairy cell leukaemia: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up
American Journal of Hematology, 2024. Hairy cell leukemia 2024: Update on diagnosis, risk-stratification, and treatment
Blood (American Society of Hematology), 2022. The International Consensus Classification of Mature Lymphoid Neoplasms

Medical disclaimerThis information is for educational purposes only and does not replace medical advice.

Last updated: 14 October 2026← Back to the list

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