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Lab tests to evaluate the T cell function
What laboratory tests can be used to evaluate the integrity of the cellular immune system (T cell function)?
A reasonable screening evaluation of T-cell function is to determine the absolute lymphocyte count and perform a Candida skin test. If these are both normal, clinically significant T-cell dysfunction may be excluded. If the Candida skin test is negative, negative delayed-type skin testing with at least four other antigens is necessary to demonstrate that T-cell function is inadequate. If these screening tests are abnormal, more sophisticated in vitro tests may be necessary to define the underlying PID disorder. HIV testing should be performed as part of the screening evaluation to exclude this acquired T-cell disorder.
Lab tests to evaluate the T cell function
| Category | Specific Tests | Comments |
|---|---|---|
| In vivo functional tests | Candida skin test | Examine degree of induration 48–72 hours later |
| (skin testing for delayed-type hypersensitivity) (routine screening tests) | PPD, Trichophyton , mumps, tetanus/diphtheria toxoid, keyhole-limpet hemocyanin | If Candida skin test is negative, testing with at least four of these antigens must be performed to determine if cell-mediated immunity is inadequate |
| Absolute lymphocyte count (routine screening test) | Determine from total WBC count and % lymphocytes | Severe cell-mediated immunity disorder unlikely in setting of normal lymphocyte count |
| In vitro tests (expensive) | Quantitation of:-Total T cells -CD4 + cells -CD8 + cells -NK cells | Specific monoclonal antibody may be used |
| Lymphocyte blastic transformation | Assessment of radiolabeled thymidine uptake following stimulation with lectins (such as PHA), specific antigen (such as Candida ), or one-way mixed lymphocyte reaction | |
| Quantitate ability of T cells to synthesize IL-2 and IL-2 receptors (CD25) | These and lymphocyte blastic transformation assay are indicators of successful T-cell activation |
IL, interleukin; PHA, phytohemagglutinin; PPD, purified protein derivative (for tuberculosis); WBC, white blood cell.
