Lymphocyte subsets (TBNK)

This test uses flow cytometry to count absolute numbers and proportions of peripheral blood T-cells (CD3, CD4, and CD8), B-cells (CD19) and NK cells (CD56/CD16) within the lymphocyte population.

Untreated HIV positive patients usually have reduced CD4 T cells or a reduced CD4/CD8 cell ratio, often in conjunction with an absolute lymphocytopaenia. Whilst a low CD4+ T cell count is no longer a criteria for starting ART (anti-retroviral therapy) in HIV positive patients, regular monitoring of CD4+ T cell counts remains an important tool for the assessment of immune reconstitution in patients with a late diagnosis and as a guide for the requirement of antimicrobial prophylaxis to prevent opportunistic infections. Regular monitoring of CD4 T cell counts is recommended in patients who choose not to start ART and in those who have just commenced or changed ART.

Measurement of TBNK subsets are included in the diagnostic criteria for SCID (severe combined immune deficiency), XLA (X-linked agammaglobulinaemia), 22q11.2 syndrome, and Goods syndrome (thymoma with immune deficiency).

Lymphocyte subsets are further used in the assessment of immune reconstitution post-transplant or post B cell depleting therapy (e.g. Rituximab).

Monitoring of HIV infection
Investigation of primary and secondary immune deficiency
Monitoring of immune reconstitution

NB values for children vary according to age

Reference ranges from Comans-Bitter WM,et al. Immunophenotyping of blood lymphocytes in childhood. Reference values for lymphocyte subpopulations. J Pediatr. 1997 Mar;130(3):388-93.