Platform
Company
Immunology & Autoimmune
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Currently under review
Pending specialist review and validation.
This test measures the absolute number of CD8-positive T cells in your blood using flow cytometry. Laboratory instruments identify white blood cells with CD45, confirm T cells with CD3, and then count the subset that carries the CD8 marker. The result reflects how many cytotoxic, or killer, T cells you have in a given volume of blood.
CD8 T cells help control viral infections and survey for abnormal cells. Your clinician may order this test on its own or as part of a lymphocyte subset panel to better understand your immune system and how it is functioning over time.
Knowing your CD8 T-cell count helps your care team assess immune status in conditions that affect T cells, such as HIV, certain viral infections, autoimmune diseases, and after organ or stem cell transplantation. It is also used to monitor recovery after chemotherapy or other treatments that suppress the immune system, and to evaluate responses to immunomodulating therapies.
Results can guide follow-up testing and treatment decisions, especially when viewed together with the total lymphocyte count, CD4 T-cell count, and the CD4/CD8 balance. If your clinician is tracking trends, this test may be repeated over time to see how your immune system is changing and to tailor care accordingly. The test uses a standard blood draw, which carries minimal risks like brief discomfort, bruising, or lightheadedness.
Your result is interpreted in the context of your overall health, symptoms, and other immune markers. A lower CD8 count can occur with some medicines that suppress immunity, after chemotherapy, during certain infections, or with nutritional or medical conditions that reduce lymphocytes. A higher count can be seen with ongoing immune activation, some infections, and in a variety of inflammatory states. Isolated changes are less informative than patterns over time.
Your clinician will typically compare this value with your CD4 T-cell count and total white blood cell and lymphocyte counts. If results are unexpected, your team may repeat the test, review medications, and consider additional evaluations such as viral load testing, immunoglobulin levels, or other immune panels. Always discuss next steps with your clinician, who will align any follow-up with your specific situation and treatment plan.
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.
Viral illnesses and recent vaccines can temporarily shift lymphocyte populations, including CD8 T cells, leading to short-term increases or decreases that may not reflect your baseline.
Corticosteroids, chemotherapy, biologics, calcineurin inhibitors, and other immunosuppressants can lower lymphocyte counts. Some antiviral or immunomodulating treatments can also change CD8 levels.
Flow cytometry is sensitive to delays and temperature during transport. Prolonged transit or improper storage can alter cell viability and surface markers, affecting the measured count.
Time of day, acute stress, strenuous exercise, and dehydration can transiently change circulating lymphocyte counts. Testing under consistent conditions reduces this variability.
Normal immune cell distributions vary by age, and underlying conditions such as autoimmune disease, chronic infection, or recovery after transplantation influence CD8 T-cell levels.
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