Platform
Company
Immunology & Autoimmune
Review status
Currently under review
Pending specialist review and validation.
This test measures the percentage of T lymphocytes, identified by the CD3 marker, among white blood cells that carry the CD45 marker. It is performed by flow cytometry, a method that labels cells with fluorescent antibodies and counts specific cell types.
CD3 is present on nearly all mature T cells, so this result reflects the relative size of your T cell compartment within the white blood cell population.
T cells help coordinate and carry out immune responses against infections and cancers. Doctors use this measurement to evaluate how well your immune system is functioning, often alongside related tests such as CD4 and CD8 T cell subsets and absolute lymphocyte counts.
It can help assess suspected immune deficiency, monitor certain infections, follow recovery after chemotherapy or transplant, and track the effects of immunosuppressive or biologic therapies.
Your result is interpreted in the context of your age, health history, symptoms, and other blood tests. A lower percentage can reflect fewer T cells or a shift in the balance of other white blood cells, while a higher percentage can occur when other cell types are reduced or when T cells are relatively more abundant.
Because this test reports a proportion, your clinician may also look at absolute counts and detailed T cell subsets to understand whether there is a meaningful immune change. If results are unexpected, your provider may repeat the test, review medications, and consider additional evaluations.
Reference intervals vary by laboratory, analyzer, methodology, population, and units. The ranges shown here are for education only. Always interpret your results against the reference interval printed on your own lab report.
Flow cytometry works best on fresh blood. Delays, extreme temperatures, or improper tube type can reduce cell viability or marker detection and subtly alter measured percentages.
Acute illness and recent immunization can temporarily shift white blood cell distributions, leading to transient changes in the proportion of T cells reported by this test.
Corticosteroids, chemotherapy, and targeted agents that affect lymphocytes can lower T cell numbers. Some monoclonal antibodies may mask cell markers or change counts for a period of time.
Normal immune composition changes with age, especially in infancy and early childhood. Interpretation always considers age-specific expectations for T cell proportions.
HIV infection, primary immunodeficiencies, autoimmune disease, and hematologic disorders can alter T cell proportions and are evaluated alongside clinical findings and other labs.
After stem cell transplant, organ transplant, or T cell–directed therapies, T cell recovery can be delayed or uneven, affecting measured percentages during immune reconstitution.
References