A flow cytometry test is one of the most important tests during the diagnostic process for chronic lymphocytic leukemia (CLL).

This test can determine that the cancer is CLL and not another form of leukemia. In addition to confirming a CLL diagnosis, the results of a flow cytometry test can also help doctors stage your cancer and get a better idea of your prognosis.

Once CLL is diagnosed and staged, doctors can work with you to determine a treatment plan.

Keep reading to learn more about the CLL flow cytometry test — when it’s used, how it works, and more.

Flow cytometry is a machine that looks for markers in or on cells that can help identify those cells. It can be used to see if white blood cells called lymphocytes are cancerous. It can also determine what type of cancer cells are present and how many cancer cells there are.

Information from a CLL flow cytometry test can help doctors:

  • confirm a diagnosis
  • identify if cells have certain markers that make them more or less aggressive
  • determine the staging of cancer
  • choose your initial treatment

Flow cytometry can also identify cancer cells in bone marrow.

Flow cytometers are able to determine the properties of individual cells. They can provide information such as:

  • cell DNA
  • cell DNA expression
  • new cell DNA
  • cell proteins
  • cell surfaces receptors
  • cell size
  • cell structure
  • cell antigen signaling

Flow cytometers get this data from a sample of a person’s blood or bone marrow. Blood or bone marrow samples are treated with specialized biologic stains called fluorochromes that highlight cellular markers. The samples are then diluted before being passed through a laser.

As the samples pass through the laser, irregular cells light up and are counted by the machine. This is processed as data that doctors can read and interpret.

The results of a flow cytometry test will show how many irregular cells are present in white blood cells or bone marrow.

A diagnosis of CLL requires at least 5,000 irregular cells per microliter of blood. Numbers beyond this can help doctors stage CLL and can help them plan your treatment.

Test results can also show specific makers that can indicate outlook. For instance, flow cytometry can detect antigens called ZAP-70 or CD38 in CLL cells. According to the American Cancer Society, people with CLL with lower numbers of these antigens may have a better overall outlook.

Flow cytometry isn’t the only test used to diagnose leukemia. Your first step will be a doctor’s appointment that will include a medical history and physical exam.

A doctor will ask you about your symptoms and will examine your lymph nodes and other areas. They might refer you to a cancer specialist for further testing.

You’ll likely have several other tests to confirm a diagnosis of CLL. These might include:

  • Complete blood count (CBC). A CBC measures the red blood cells, white blood cells, and platelets in your blood. People with CLL often show too many lymphocytes, which are a type of white blood. They might also have a low level of red blood cells and platelets.
  • Peripheral blood smear. A peripheral blood smear looks at a sample of your blood under a microscope to see how many of your lymphocytes look abnormal.
  • Bone marrow biopsy and aspiration. Bone marrow biopsies and aspirations remove samples of your bone marrow fluid and bone marrow so they can be tested in a lab. They’re done by inserting two long and thin needles into your hip bone. The first needle removes the sample of bone marrow fluid, and the second needle removes the bone marrow.
  • Cytogenetic tests. Cytogenetic tests use samples of bone marrow cells to grow new cells in a lab. This allows doctors to see the chromosomes of a person with CLL and can help determine outlook.
  • Fluorescent in situ hybridization (FISH). A FISH test looks at the chromosomes already present in blood or bone marrow samples. The test uses a special dye to look for changes that are associated with CLL.
  • Imaging tests. Imaging tests such as MRIs and X-rays aren’t normally part of CLL testing. However, you might have them done if your doctor suspects swelling in your lymph nodes or any organs.

The results of all your tests will be used to determine the stage and progression of your cancer. Doctors factor in other information such as your age and overall health to come up with the best treatment plan for you.

You and your doctor can discuss available treatment options and what they would mean for you. You can proceed with a treatment plan decided upon by you and your doctor or take your results to another cancer specialist to get a second option and more treatment options.

Either way, once you have a diagnosis, you’ll be able to make choices and start treatment.

Flow cytometry is part of the CLL diagnostic process. It helps diagnose CLL and rule out other types of leukemia.

The test is able to read information about individual cells. It can help determine how many lymphocytes are cancerous. This can confirm a diagnosis of CLL, stage CLL, help determine treatment, and indicate the outlook.

Flow cytometry isn’t the only diagnostic test for CLL but it’s one of the most important.