Acute myeloid leukemia diagnosis
Fact-checked by Establishing an acute myeloid leukemia (AML) diagnosis and determining the disease subtype requires several tests to identify and characterize cancerous cells in the blood and bone marrow. These typically include blood tests, microscopic bone marrow analyses, and cellular and molecular analyses.
Collectively, these test results guide treatment decisions and help doctors predict a person’s prognosis. After an AML diagnosis, doctors may repeat certain diagnostic tests throughout treatment to evaluate how the cancer is responding.
How is AML diagnosed?
AML is largely diagnosed based on the presence of cancer cells in the blood and bone marrow — the spongy interior of some bones where blood cells are made.
The process often begins when a person develops characteristic symptoms, which typically emerge rapidly over a few weeks. If AML is suspected after a thorough physical exam and review of medical history, a doctor will order diagnostic tests to look for cancerous cells, which in AML are immature blood cells called blasts.
Normally, blasts make up no more than 5% of all cells in bone marrow and are not present in the blood. In AML, blast cells grow out of control in the bone marrow and enter the bloodstream.
An AML diagnosis traditionally requires that blasts account for at least 20% of cells in the blood or bone marrow, though this threshold may be lower when certain genetic features are present. Identifying these genetic features also pinpoints the AML subtype, which informs treatment options.
Throughout treatment, doctors may repeat these tests to measure how many cancer cells remain. The small number of leukemia cells that persist after treatment is called measurable residual disease, or MRD.
Diagnostic tests for AML
Most diagnostic tests for AML require samples of blood or bone marrow. Blood is taken from a vein in the arm, while bone marrow is collected using a thin needle inserted into a bone, usually in the back of the hip. Healthcare providers may extract both bone marrow fluid (bone marrow aspiration) and a solid sample of bone and marrow (bone marrow biopsy).
Several different tests may be used to analyze these samples to identify AML and its subtypes. These include:
- complete blood count: measures the number of different blood cell types in the blood
- microscopic examination: identifies cancerous cells in blood or bone marrow samples
- flow cytometry: helps confirm the presence of cancer cells and their type
Complete blood count
A complete blood count (CBC) is often among the first blood tests for AML. It can’t confirm a diagnosis on its own, but it can flag AML as a possible explanation for symptoms.
The CBC measures the numbers of all blood cell classes. It usually includes a white blood cell differential, which counts individual white blood cell types. CBC results in AML often show:
- low levels of red blood cells and platelets
- high levels of white blood cells
While the number of healthy, mature white blood cells is often low in AML, the overall white blood cell count can be high due to an increase in cancerous blast cells. The white blood cell differential can help flag whether there is an unusual percentage of blast cells.
Microscopic analysis
Examining blood and bone marrow samples under a microscope helps doctors better understand the size, shape, maturity, and other characteristics of blood cells.
Doctors use this to identify cancerous blast cells and determine their proportion relative to healthy blood cells. Cell features observed under a microscope can also provide clues about the AML subtype.
Flow cytometry
Flow cytometry is a specialized technique that helps confirm and characterize AML. It uses antibodies to detect protein markers found on the surface of leukemia cells — a process called immunophenotyping.
Flow cytometry in leukemia helps determine the specific type of blast cells present, which differentiates AML from other diseases characterized by abnormal blast cells, such as acute lymphoblastic leukemia.
Due to its high sensitivity, this test is often repeated during treatment to detect MRD.
How doctors identify the AML subtype
There are two main sets of AML diagnostic criteria: the World Health Organization criteria and the International Consensus Criteria. While their specifics vary, both classify disease subtypes based on the presence of specific AML genetic mutations, which also informs whether AML can be diagnosed with a blast threshold below 20%. There are also nongenetic subtypes related to cell maturity or a patient’s medical history.
Doctors identify the AML subtype based on the characteristics of a person’s cancer cells in blood or bone marrow samples. Genetic and molecular testing in AML may include:
- cytogenetic analysis: identifies abnormalities in chromosomes, the structures that cells use to store DNA
- DNA sequencing or polymerase chain reaction (PCR): identifies gene mutations linked to AML subtypes
Also called karyotyping, cytogenetic testing for AML involves isolating blasts from blood or bone marrow samples, growing them in a laboratory setting, and examining their chromosomes under a microscope. In AML, chromosomes can be rearranged, duplicated, or have parts deleted or added.
Other tests identify genetic mutations in cancer cells that cannot be seen under a microscope. In AML, these disease-associated mutations are usually acquired throughout life — they are not inherited at birth.
DNA sequencing is often performed at diagnosis and repeated later to see if a person’s cancer cells have acquired new mutations over time.
Polymerase chain reaction is a highly sensitive genetic testing method that can detect rare or small mutations that other approaches miss. It is used to help determine the disease subtype at diagnosis and repeated later to detect MRD, because it can identify the very small group of blasts that remain alive after treatment.
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| Test | What it measures |
|---|---|
| Complete blood count | Counts the number of each blood cell type, which offers clues that more testing is needed |
| Microscopic analysis | Identifies the presence and proportion of abnormal blast cells, the defining feature of AML |
| Flow cytometry | Confirms the type of abnormal blast cells, which distinguishes AML from other blood disorders |
| Cytogenetics | Identifies chromosomal abnormalities in cancer cells, which informs the AML subtype |
| DNA sequencing and PCR | Identify genetic mutations in cancer cells, which inform the AML subtype |
Tests used to assess overall health before treatment
In addition to diagnosis and subtype identification, the AML testing process typically involves measuring a patient’s overall health. Certain types of intensive chemotherapy require that a person have good general health before treatment starts. These tests may measure:
- blood chemistry, which helps evaluate organ health, blood sugar, cholesterol levels, and other factors
- ability to complete daily tasks
- heart and lung function
- cognitive abilities
- psychiatric health
- other health conditions that someone has alongside AML
How long AML test results can take
The timeline for receiving AML test results depends on the specific test type and the testing facility. Patients should ask their healthcare team when to expect results in their case.
In general, the results of blood tests like a CBC come back very quickly — often within a few hours to a day — while more specialized AML tests, such as cytogenetic analyses, can take a week or longer.
Questions to ask when reviewing a new diagnosis
An AML diagnosis can bring up many questions and concerns. Patients should talk with their care teams about what to expect next. It may be helpful to ask about:
- whether any follow-up testing is required before treatment starts
- treatment options and recommended timelines
- the prognosis for their AML subtype
- if referrals to other specialists are recommended
- available resources for information, patient support, financial aid, or mental healthcare
Rare Cancer News is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.
