Reviewing the Role of B Cell Subset Enumeration in the Paediatric Population

Introduction B cell subset enumeration by flow cytometric method has historically primarily existed to assist in the prognostic classification of common variable immunodeficiency (CVID) patients, and diagnostic reporting practices reflect this. Recently, there has been a noticeable increase in requests in the pediatric population for other indications that may require a different reporting strategy. Proposed indications include further immunophenotyping of inborn errors of immunity (IEIs), especially in humoral deficiencies or immune dysregulation disorders and/or monitoring for reconstitution following stem cell transplant (SCT) or immune-targeting therapies. Method A retrospective audit of paediatric patients (aged under 18 years) who had B cell subset enumeration performed at Immunopathology, Pathology Queensland Central Laboratory over a 12-month period between 1 January, 2024 and 31 December, 2024. We audited the demographics, ordering indication, ordering clinician specialty, concurrent immunoglobulin levels, B cell subsets, and whether the result contributed to diagnosis or management. Results There were 97 distinct B cell subset tests from 95 separate patients. 34 patients were excluded due to insufficient clinical information. Most requests were for assessment of humoral immunodeficiency, either immune phenotyping in a known diagnosis or screening in suspected cases. Conclusion This audit demonstrated that the majority of paediatric requests for B cell subset enumeration are not for CVID subclassification and are for broader indications. This highlighted the need to update B cell subset reporting strategies to greater reflect these indications and assist the clinical application.