Tests for Acute Lymphocytic Leukemia (ALL)

Blood samples for ALL tests are generally taken from a vein in the arm.

Complete blood count (CBC) and peripheral blood smear: These are often the first tests done on people with a suspected blood problem.

• The CBC measures the number of red blood cells, white blood cells, and platelets in your blood. It is often done along with a differential (or diff) which looks at the amounts of each type of white blood cell.
• For a peripheral blood smear (sometimes just called a smear), a drop of blood is smeared across a slide and then looked at under a microscope. Changes in the number and appearance of the cells can often help diagnose leukemia.

Most people with ALL have too many immature white blood cells in their blood (called lymphoblasts or just blasts) and not enough red blood cells or platelets.

Lymphoblasts aren’t normally found in the blood, and they don't function like normal, mature white blood cells. These findings may suggest leukemia, but the disease usually isn’t diagnosed without looking at a sample of bone marrow cells (see below).

Other tests to look for leukemia cells: Several other lab tests might be done on blood samples to look for leukemia cells. These are described below in ‘Lab tests to diagnose and classify ALL’.

Blood chemistry tests: These tests measure the amount of certain chemicals in your blood. They aren’t used to diagnose leukemia, but they can help find liver or kidney problems caused by spreading leukemia cells or the side effects of certain chemotherapy drugs. They also help determine if treatment is needed to correct low or high blood levels of certain minerals.

Coagulation tests: Blood coagulation tests may be done to see if your blood is clotting properly.

Leukemia starts in the bone marrow, so checking your bone marrow for leukemia cells is a key part of testing for it. Samples for testing are collected by bone marrow aspiration and biopsy.

These tests are usually done at the same time. The samples are most often taken from the back of the pelvic bone (hip), although they are sometimes taken from other bones. If only an aspiration is done, it might be taken from the sternum (breastbone).

Bone marrow aspiration:

For this procedure, you lie on a table (either on your side or your belly). After cleaning the skin over your hip, the doctor numbs the skin and the surface of the bone by injecting a local anesthetic. This may cause a brief stinging or burning sensation.

The doctor then inserts a thin, hollow needle into the bone, and uses a syringe to suck out a small amount of liquid bone marrow. Even with the anesthetic, most people still have some brief pain when the marrow is removed.

Bone marrow biopsy:

A bone marrow biopsy is usually done just after the aspiration. The doctor removes a small piece of bone and marrow by pushing a slightly larger needle into the bone. This also might cause some brief pain. Once the biopsy is done, pressure is applied to the site to help prevent bleeding.

These bone marrow tests help diagnose and classify leukemia. See “Lab tests used to diagnose and classify ALL” below for more on the tests that might be done on these samples.

Bone marrow tests may also be done again later to check if the leukemia is responding to treatment.

ALL sometimes spreads to the area around your brain and spinal cord. This area is surrounded by cerebrospinal fluid (CSF). To check for cancer spread, doctors remove and test a sample of CSF.

You may lie on your side or sit up for this test. First, the doctor numbs an area in the lower part of your back over your spine. Then they collect fluid through a small, hollow needle placed between the bones of your spine and into the area around your spinal cord.

See “Lab tests used to diagnose and classify ALL” below for more on tests that might be done on these samples.

A lumbar puncture can also be used to put chemotherapy drugs into the CSF to try to prevent or treat the spread of leukemia to the spinal cord and brain.

An enlarged lymph node or part of a lymph node might be removed (biopsied), but this is rarely done to test for ALL because the diagnosis is usually made with samples of blood and bone marrow.

In this procedure, a surgeon cuts through your skin to remove all or part of a lymph node.

• Excisional lymph node biopsy: entire lymph node is removed
• Incisional lymph node biopsy: part of a lymph node is removed

If the node is just under your skin, this is often done with local anesthesia (numbing medicine). If the node is inside your chest or abdomen, general anesthesia is used to keep you asleep during the biopsy.

A pathologist (a doctor specializing in lab tests) will look at your bone marrow samples with a microscope. A hematologist/oncologist (a doctor specializing in cancer and blood diseases) may review these as well. These doctors might also look at your blood or CSF samples.

They will classify the white blood cells in the samples by looking at their size, shape, and other traits.

Looking for lymphoblasts (blasts):

• A key factor is whether the cells look mature (like normal blood cells) or immature.
• The most immature blood cells are called lymphoblasts, or just blasts.

The percentage of blasts in your bone marrow:

• An important part of diagnosing ALL is the percentage of blast cells in your bone marrow.
• Normally, blasts make up no more than 5% of bone marrow cells.
• A diagnosis of ALL generally requires that blasts make up at least 20% of bone marrow cells.

In this test, cells are exposed to chemical stains that react only with some types of leukemia cells, causing them to change color. Cytochemistry is rarely done anymore. It has largely been replaced by flow cytometry and immunohistochemistry.

For both flow cytometry and immunohistochemistry (IHC), samples of cells are treated with antibodies (proteins that stick only to certain other proteins on cells).

• For IHC, the cells are looked at under a microscope to see if the antibodies stick to them.
• For flow cytometry, a special machine uses a laser to measure and sort the cells.

These tests are used for immunophenotyping — classifying leukemia cells according to proteins (antigens) on or in the cells. This helps doctors figure out the type of leukemia you have. If doctors already think you have ALL, the tests can help determine the exact subtype.

These tests are most often done on cells from bone marrow, but they can also be done on cells from the blood, lymph nodes, and other body fluids.

Some tests look at the chromosomes (long strands of DNA) inside the cells. Normal human cells have 23 pairs of chromosomes. ALL cells sometimes have chromosome changes that can be found with a microscope or other tests.

Recognizing these changes can help identify certain subtypes of ALL. It can also help determine a person’s outlook and likely response to some treatments.

• Looking for translocation in ALL cells: The most common chromosome change in ALL cells is a translocation. This is when 2 chromosomes swap some of their DNA so that part of one chromosome attaches to part of a different chromosome.
• The Philadelphia chromosome: The most common chromosome change in adult ALL is a translocation that results in a shortened chromosome 22 (called the Philadelphia chromosome). This change is especially important because it can be targeted with certain drugs.

Cytogenetics (karyotyping)

For this test, cells are grown in lab dishes until they start dividing. Then the chromosomes are stained and looked at under a microscope to detect any changes. Because it takes time for the cells to start dividing, cytogenetic testing often takes a week or more.

Not all chromosome changes can be found this way. Some are too small to see under a microscope. Other lab tests (like FISH and PCR, discussed below) can often help find these changes.

Fluorescent in situ hybridization (FISH)

This test uses special fluorescent dyes that only attach to certain genes or parts of specific chromosomes.

• It can find most chromosome changes that are seen under a microscope in standard cytogenetic tests, including translocations.
• It can also find some changes too small to be seen with usual cytogenetic testing.

FISH can be used on regular blood or bone marrow samples, or on cells from lymph node samples or other tissues. It is very accurate and usually provides results within a few days.

FISH only tests for certain gene changes. It doesn’t look at the chromosomes overall. So this test is best when looking for specific gene changes based on the kind of leukemia a person has.

Polymerase chain reaction (PCR)

This is a very sensitive DNA test. Like FISH, it can find certain gene and chromosome changes too small to be seen with a microscope, even if very few leukemia cells are present in a sample.

Also like FISH, it is used to look for specific gene changes and not at the chromosomes overall.

If a person’s leukemia cells have a specific gene or chromosome change, doctors can use PCR to help determine how the leukemia responded to treatment by looking for even small numbers of leukemia cells that may not be visible with a microscope.

Other lab tests can also be done on the tissue and cell samples to look for specific gene changes, as well as other changes in the leukemia cells. Many of these tests are done using next-generation sequencing (NGS), which looks at the code of long strands of DNA (including its genes) all at once.

Some of the changes found on these tests help doctors learn more about the leukemia. Some can even help tell if certain treatments are likely to be helpful.

• To learn more about the lab tests above, see Tests Used on Biopsy and Cytology Samples to Diagnose and Classify Cancer.
• For more on some of the gene and chromosome changes seen in ALL cells, see Acute Lymphocytic Leukemia (ALL) Subtypes and Prognostic Factors.

You might get a chest x-ray if your doctor suspects you have a lung infection. It may also be used to look for enlarged lymph nodes in your chest (although a CT scan of the chest is more often done for this).

A CT scan uses x-rays to make detailed, cross-sectional images of your body.

This test can be used to see if the leukemia is affecting any lymph nodes or organs in your body, such as your spleen, liver, or brain. It isn’t usually needed to diagnose ALL, but it may be done if you’re having signs or symptoms that suggest leukemia cells might be growing outside your blood and bone marrow.

Sometimes a test that combines the CT scan with a PET (positron emission tomography) scan (PET/CT scan) is done.

MRI scans make detailed images of your body using radio waves and strong magnets instead of x-rays.

MRIs are very helpful in looking at the brain and spinal cord. This test might be done if a lumbar puncture finds leukemia cells in your CSF, or if you’re having symptoms that suggest the ALL might have spread to the area around your brain.

Ultrasound uses sound waves and their echoes to make pictures of internal organs or masses.

This test can be used to look at lymph nodes near the surface of your body or to look for enlarged organs inside your abdomen, such as your liver, spleen, and kidneys. It can also be used to look at the testicles in men if needed.