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Immunology & Autoimmune
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Currently under review
Pending specialist review and validation.
This blood test measures the absolute number of CD3-positive T lymphocytes, a major group of white blood cells that help coordinate and carry out immune responses. The analysis uses flow cytometry, applying CD45 to identify all white blood cells and CD3 to pinpoint T cells within that population.
Your result reflects how many T cells are present in a set volume of blood. It is commonly reported alongside other lymphocyte subsets, such as CD4 and CD8 T cells, to build a more complete view of immune status.
Clinicians use this test to evaluate how well your immune system is functioning. It can aid in diagnosing or monitoring conditions that affect T cells, including immunodeficiencies, infections such as HIV, autoimmune disorders, lymphoproliferative diseases, and the effects of treatments that suppress or restore immunity.
Results can help guide decisions about further testing, preventive care, and therapies. The test is often ordered when there are frequent or unusual infections, unexplained lymphocyte changes on a complete blood count, before and after transplantation, during chemotherapy or biologic therapy, or when tracking recovery from an illness.
Your healthcare provider will interpret the result in context with your symptoms, history, and other laboratory findings. A lower count can be related to medications that suppress the immune system, certain infections, congenital immune conditions, malnutrition, or severe illness. A higher count can be seen with active infection, inflammation, recovery phases, or some lymphoproliferative conditions.
A single measurement rarely tells the whole story. Trends over time and the balance with other lymphocyte subsets often provide more insight. If a result is unexpected, your clinician may repeat the test, review medications and recent illnesses, or order additional immune studies to clarify the cause.
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.
Lymphocytes are sensitive to delays between collection and analysis. Prolonged transport, extreme temperatures, clotting, or inadequate mixing can reduce viable cells and alter flow cytometry gating, affecting the reported count.
Active infections or a recent vaccine can temporarily shift T cell numbers and distribution. Counts may fluctuate during illness and recovery, so timing relative to symptoms or shots can influence the result.
Corticosteroids, chemotherapy, biologic agents, and other immunosuppressants often lower circulating T cells. Some antivirals and growth factors can also affect counts, so share all medications and therapies with your care team.
Normal daily rhythms, standing versus lying down, and recent strenuous activity can change lymphocyte trafficking. These physiologic shifts can cause modest differences in a single measurement.
Pregnancy, early life, and older age are associated with shifts in lymphocyte subsets and distribution. In these groups, interpretation relies heavily on clinical context and may prioritize trends over a single value.
Flow cytometry panels, antibody clones, and gating strategies vary across laboratories. Using the same laboratory for follow-up testing improves comparability of results over time.
References