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Immunophenotyping

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Also known as: Immunophenotyping by Flow Cytometry or Immunohistochemistry
Formal name: Immunophenotyping

The Test Sample

What is being tested?

Immunophenotyping detects the presence or absence of white blood cell (WBC) antigens. These antigens are protein structures found on the surface or interior of WBCs. Typical groupings of antigens are present on normal WBCs and are unique to specific cell types. Atypical but characteristic groupings are seen with leukemias and lymphomas. This allows immunophenotyping to be useful in helping to diagnose and classify these blood cell cancers.

Leukemias and lymphomas are caused by an abnormal cell that begins to clone itself uncontrollably. The abnormal lymphocytes or myeloid (granular) monoclonal cells proliferate, yet do not fight infections or perform other functions like normal WBCs. Because they do not die at a normal rate, they accumulate in the bone marrow, in a lymph node, or in other tissues, where they grow in numbers. As the number of cells increases in the bone marrow, they may crowd out and inhibit the production of normal red and white blood cells. Eventually, the abnormal cells will also be released into the bloodstream.

CBC (complete blood count) and differential tests performed on a sample of blood from someone with leukemia or a lymphoma may reveal an increased number of white blood cells with a predominance of one type. These tests may suggest lymphoma or leukemia, but more information is generally needed to confirm a diagnosis. CBC and differential testing cannot confirm the presence of monoclonal WBCs or detect the subtle differences that may exist between different types of blood cell cancers.

With immunophenotyping, a blood, bone marrow, or other tissue sample can be tested to gather this information – information that is then used to identify a specific type of leukemia or lymphoma and, where possible, used to predict its likely aggressiveness and/or responsiveness to certain treatment. The identification of different types of leukemias and lymphomas is based upon the presence or absence of antigens and a typical pattern that has been established with each leukemia/lymphoma.

Immunophenotyping detects the presence or absence of antigens found on the surface or interior of blood cells. Atypical or abnormal cells can demonstrate characteristic antigen groupings that are consistent with specific types of leukemia and lymphoma. The identifications made are based upon a "library" of antigen associations and patterns that have been established over time.

Most of the antigens that immunophenotyping detects are identified by a CD (clusters of differentiation or cluster designation) number (see the table in the "What does the test result mean?" section). CD numbers represent a naming convention that is based upon international consensus. While hundreds of antigens have been identified and have received a unique CD number, only a small number of these are routinely used.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm. A bone marrow aspiration and/or biopsy procedure is performed by a trained health practitioner. Fluid samples are obtained through collection of the fluid in a container or by inserting a needle into the body cavity and aspirating a portion of the fluid with a syringe. Sometimes, a tissue sample, such as from a lymph node, is obtained using a biopsy procedure.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.