Cautions

T-cell counts should be appropriately interpreted in context of the clinical presentation and other immunological parameters and relevant laboratory test results.

For serial monitoring of T-cell numbers, it is recommended that the patient be evaluated at the same time of the day to account for diurnal variation.

For follow-up of infants identified by newborn screening for severe combined immunodeficiency (SCID) and severe T-cell lymphopenia, SCID should be considered as a potential diagnosis in infants with fewer than 300 autologous CD3 T cells/mcL. Infants with 300 to 1500 autologous CD3 T cells/mcL may have leaky SCID, Omenn syndrome, or variant SCID, depending on other clinical and molecular features.

In infants identified by newborn screening for SCID, T-cell lymphopenia is defined as autologous CD3 T cells at or below 1500 cells/mcL.

This assay should not be used for diagnosing T-lymphocytic malignancies or evaluation of T-cell lymphocytosis of unknown etiology, though the latter may be identified through this assay in a screening assessment. In such cases, LCMS / Leukemia/Lymphoma Immunophenotyping, Flow Cytometry, Varies will be recommended, which includes a hematopathology review.

Also, when diagnostically assessing lymphocyte subsets (quantitatively) in any of the above clinical contexts, it may be more useful to order the T-cell, B-cell, and natural killer(NK) cell quantitation assay rather than the T-cell subset quantitation alone, as it excludes B-and NK-cell counts.