X-linked agammaglobulinaemia (XLA) is caused by mutation of the BTK gene. Early immunological screening is important in children with recurrent infection to avoid delay in diagnosis and treatment. A 9-year-old boy with delayed XLA diagnosis presented with a history of recurrent sinopulmonary infection since the age of 1 year old. He had a severe Achromobacter xylosoxidans bacteraemia at the age of 8 years that was successfully treated with intravenous antibiotics. Further immunological screening and genetic testing confirmed the diagnosis of XLA and he was treated with intravenous immunoglobulin replacement therapy. This case provides a valuable information on the diagnosis, treatment and management of XLA, emphasising the importance of early immunological investigations to avoid diagnostic delay.

Flow cytometer, a machine that utilizes the usage of light signals, has become one of the important machines or components in the studies of specific cell populations, cell surfaces, or even in detecting intracellular proteins. Due to its multiplex functionalities, while at the same time being very sensitive and specific, flow cytometer, or the technique of flow cytometry, has become a favourable and valuable tool for immunologists and clinicians for initial diagnosis of primary immunodeficiency diseases (PID), especially in studying cellular functional characteristics linked to PID. This paper will review key immunology tests of clinical flow cytometry, specifically in immunophenotyping, T cells classification and lymphocyte proliferation assays for their advantages and limitations in the field of PID. Importance of validation for the assays will be discussed. It is expected that development of validated immunology tests in clinical flow cytometry for PID diagnosis ensure standardized protocols, improve troubleshooting and disease interpretation, and improve the quality in patients’ diagnosis and management.
Flow cytometry