Diagnosis

An accurate diagnosis of the type of leukemia is important. The exact diagnosis helps the doctor estimate how the disease will progress and determine the appropriate treatment.

Diagnosing acute myeloid leukemia (AML) and the AML subtype usually involves a series of tests. Some of these tests may be repeated during and after therapy to measure the effects of treatment.

Blood and bone marrow tests are used to diagnose AML and the AML subtype. A change in the number and appearance of blood cells helps to make the diagnosis.

Blood samples are generally taken from a vein in the arm. The blood sample is sent to a lab for testing.

Complete Blood Count (CBC) with Differential

This test measures the number of red blood cells, white blood cells, and platelets. Children with AML often have a high number of white blood cells, but most of these are leukemic blast cells that do not protect against infection. They also usually have a low number of red blood cells and platelets.

Even if blood test results suggest that your child has leukemia, an AML diagnosis is usually made only after the examination of the bone marrow cells.

Bone Marrow Test

Samples of marrow cells are obtained by bone marrow aspiration and biopsy. Bone marrow testing involves two steps usually performed at the same time in a doctor's office or a hospital:

  • A bone marrow aspiration to remove a liquid marrow sample
  • A bone marrow biopsy to remove a small amount of bone filled with marrow

Bone marrow samples are usually taken from the hip bone. Both samples are examined under a microscope to look for chromosomal and other cell changes.

Lumbar Puncture

AML cells can spread to the cerebrospinal fluid, the fluid that flows around the brain and spinal cord. After the area over the spine in the lower part of the back has been numbed with local anesthesia, a thin needle is inserted between two vertebrae (back bones) and into the cerebrospinal fluid. The sample is sent to a lab for testing.

Cell Assessment

Blood, bone marrow, and cerebrospinal fluid samples are examined under a microscope to determine if the cells look like normal, mature blood cells or abnormal, immature blood cells (blast cells).

Typically, there are no blast cells in the blood, and no more than 5 percent of the cells in the bone marrow are blast cells. A diagnosis of AML generally requires a finding of 20 percent or more of the cells in the bone marrow sample to be myeloid blast cells.

Immunophenotyping (Flow Cytometry)

A flow cytometry test can measure the number and specific characteristics of cells in a sample (such as their size and shape), as well as identify specific markers on the cell surface. Leukemia cells can have different antigens on their surfaces, depending on the type of leukemia. In addition to its use as a diagnostic test, flow cytometry is also used after treatment for evaluating minimal/measurable residual disease (MRD), which refers to the small number of cancer cells that may remain in the body after treatment. 

Cytogenetic Analysis (Karyotyping)

This test uses a microscope to examine the chromosomes inside the cells. Chromosomes are the part of a cell that contains genetic information. Normal human cells contain 23 pairs of chromosomes, for a total of 46 chromosomes. The chromosomes are a certain size, shape and structure. In some cases of AML, the chromosomes of the leukemia cells have abnormal changes.

Cytogenetic testing is done with either a bone marrow or blood sample. The leukemia cells are allowed to grow in a laboratory and then stained. The sample is then examined to see the arrangement of the chromosomes, called a “karyotype.” The karyotype shows if there are any abnormal changes in the leukemia cells. In some cases, this provides important information to determine treatment options and prognosis.

Fluorescence In Situ Hybridization (FISH)

This very sensitive test is used to examine genes or chromosomes in cells and tissues. Doctors use FISH to detect certain abnormal changes in the chromosomes and genes of leukemia cells. Pieces of DNA that contain special fluorescent dyes are prepared in the laboratory and added to the leukemia cells on a glass slide. The pieces of DNA that bind to certain genes or areas of chromosomes light up when the slide is viewed under a specialized “fluorescence” microscope. Not only can FISH identify most abnormal changes that can be seen with karyotype testing under a microscope, but it can also detect some changes that are too small to be seen with karyotype testing. It is not, however, used as a general screening tool. FISH has one disadvantage—before the test is performed, the doctor must select the specific chromosomes or genes that are going to be examined.

Polymerase Chain Reaction (PCR)

This is a very sensitive test that finds and measures genetic mutations and chromosome changes that are too small to be seen with other tests or even with a powerful microscope. PCR can find a single leukemia cell in approximately 100,000 normal cells. This test is given during treatment or after treatment, and the results allow doctors to determine the amount of minimal/measurable residual disease (MRD), the small number of cancer cells left in the body after treatment.

Biomarker Testing

Biomarker testing, also called “molecular testing” or “genomic testing” refers to a number of different laboratory tests that examine the exact sequence (order) of DNA or RNA. This makes it possible to identify a variety of genetic changes in a patient’s cancer cells. These changes are important in guiding risk assessment and prognosis and may also inform treatment decisions. The information it provides can help doctors to determine which patients are at high risk and may need more intensive treatment or may benefit from treatment with novel therapies.

There are targeted sequencing tests (also called “multigene panels”) that look for specific mutations in the cancer cells. These tests focus on specific sets of genes or areas of DNA. There are also broad DNA sequencing tests (genomic screening tests) that analyze the sequence of large regions of DNA, rather than looking for mutations of specific genes. Doctors may also order sequencing of all the DNA in your entire genome. This test is known as “whole genome sequencing.”

The term “next-generation sequencing (NGS)” is a catch-all term used to describe a number of different modern sequencing technologies. These technologies allow for sequencing of DNA and RNA much more quickly and cheaply than sequencing methods that were used previously.

Since the introduction of DNA sequencing, the number of mutated genes that can be detected in AML patients has increased considerably. These markers are important in guiding risk assessment and prognosis and are also used to guide treatment decisions.

Generally, biomarker testing should be done when the cancer is first diagnosed and again after a relapse. This is because patients may acquire additional genetic abnormalities after they complete their initial, “first-line” treatment.

Pre-Treatment Tests

After your child has been diagnosed with AML and before they start treatment, tests will be done to learn more about your child’s overall health. Tests may include:

  • Blood chemistry profile
  • Human leukocyte antigen (HLA) typing
    • An HLA test is done before allogeneic stem cell transplantation to find out if there is a tissue match between a potential donor and the patient.
  • Echocardiogram to test heart function

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