Lymphocyte immunophenotyping

5-10 mL blood in lithium heparin, ACD or EDTA.

Peripheral blood mononuclear cells are incubated with fluorescent labelled monoclonal antibodies directed against specific lymphocyte surface antigens.

Detection of these antigens allows quantitation of total B cell numbers (CD19) and total T cell numbers (CD3), identification and quantitation of T cell subsets (CD4, CD8) and natural killer (NK) cells (CD16).

Cells are enumerated by Flow cytometry.

Affected by age and gender, diurnal rhythm and other physiological variables - consult pathologist.

See Table 5.

Assessment of immune deficiency states, lymphocytosis of unknown aetiology, diagnosis of lymphoid malignancies.

More extensive 'Flow cytometry' analysis is required for investigation of haematological malignancies.

Lymphocyte numbers and CD4/8 ratio are interpreted in conjunction with clinical findings, lymphocyte morphology and other immune measurements.

In HIV infection, low absolute CD4 count (< 0.35 x 10⁹/L) is predictive of disease progression, and < 0.20 x 10⁹/L CD4 is associated with an increased risk of opportunistic infection.

T cells are increased in reactive disorders and in some infections (eg, Infectious mononucleosis).

B cells (CD19) are absent in X-linked hypogammaglobulinaemia but are usually present in common variable immunodeficiency. Increased B cell numbers occur in B cell proliferative diseases; monoclonality suggests leukaemia/lymphoma.

NK (CD16) cell numbers are reduced in some immunocompromised patients, patients with cancer, and in Chediak Higashi syndrome. NK cells may be increased in reactive conditions, hepatitis C virus infection, IV drug abuse, lymphomas.

See also Flow cytometry, Table 1, Table 2.