Immunophenotyping

What is immunophenotyping?

Immunophenotyping is a lab test that checks cells for signs of cancer, especially types of leukemia and lymphoma. During the test, a pathologist checks for proteins called antigens on white blood cells. The presence (or absence) of the antigens provides clues about whether the cells are healthy or malignant (cancerous).

The word “immunophenotyping” provides clues about what’s involved:

• Immuno means having to do with your immune system. During the test, a pathologist uses immune system proteins called antibodies to detect antigens on cells. Antibodies and antigens are like a unique lock and key combo. Specific antibodies (key) bind to specific antigens (lock) on cells.
• A phenotype involves observable traits. Pathologists know that a cell contains the antigen if they see signs that the antibody attached.

The antigens a cell has allow pathologists to identify it as a cancer cell. Immunophenotyping can help pathologists determine the type of cancer cell based on its antigens.

When is immunophenotyping performed?

Your healthcare provider may order this test if the results of a complete blood count (CBC) reveal high levels of abnormal white blood cells. This can be a sign of certain blood cancers. Immunophenotyping can help your provider get closer to a diagnosis.

Immunophenotyping also allows researchers to learn more about how cancer cells with specific antigen markers respond to cancer treatments, like immunotherapy drugs.

How does the test work?

Most of the work in immunophenotyping happens behind the scenes in a lab, after you’ve had a procedure to remove a tissue or fluid sample. Most providers use a lab technique called flow cytometry to perform immunophenotyping. Less often, they use a technique called immunohistochemistry (IHC).

Flow cytometry technique

Flow cytometry allows providers to test large samples of blood or blood cells taken from tissue. A healthcare provider will:

1. Collect the sample: Usually, the sample is bone marrow taken during a bone marrow biopsy or blood removed during a blood draw. Sometimes, the sample comes from spinal fluid or fluid in your abdominal cavity.
2. Preserve the sample: Providers working in the lab will take steps to prepare the sample for immunophenotyping. This may involve adding substances so the cells don’t die.
3. Add the antibody: They’ll add the antibodies designed to attach to the target antigen. The antibodies are linked to a “fluorescent compound” or immunofluorescence marker. The marker causes the cells to generate light if the antibody attaches to the antigen.
4. Perform flow cytometry: A provider places the prepared sample with the antibodies into a flow cytometer. This machine has special detectors that can detect the light from the immunofluorescence marker. The flow cytometer measures how many cells show signs (the light) of antigen-antibody attachments.

Immunohistochemistry technique (IHC)

Immunohistochemistry allows providers to test a specific tissue sample for antigens. The steps that take place in the lab are similar to flow cytometry. The biggest difference is that with IHC, providers add an enzyme to the antibodies instead of a fluorescent compound. The enzyme stains cells a certain color if they have the target antigen. If a provider sees the color stain when they look at the sample beneath a microscope, the cells contain the target antigen.

What are the limitations of immunophenotyping?

The biggest limitation is that there aren’t standard procedures that all labs performing this test follow. This means that there can be some variation in results.

It’s important to remember that healthcare providers consider the results of immunophenotyping alongside other factors, like your symptoms and other test results, before making a diagnosis. This means that you’re unlikely to receive a cancer diagnosis based on this test alone. It’s one helpful source of information your provider can use to learn more about your health.

What type of results do you get, and what do the results mean?

Your healthcare provider will explain what your results mean based on the pathologist’s analysis. The results of an immunophenotyping test aren’t straightforward. It takes a trained pathologist to interpret the data that the flow cytometer generates about the sample.

This includes information like:

• The type of white blood cells.
• Their stage of development.
• How many cells contain the target antigen.

A pathologist compares this data from your sample with data taken from people without cancer. They also compare your results to results from people with specific leukemias or lymphomas. Based on these patterns (and the results of other tests), they determine the likelihood that you have the cancer they’re testing for.

When should I call my healthcare provider?

Call your healthcare provider if you’re unsure when you’ll receive your results or are confused about what they mean. Immunophenotyping is a complex lab procedure that provides information about complex cell characteristics. But your healthcare provider can explain what this means for your health.