This study aimed to establish the reference intervals for the 3H thymidine uptake assays of functional cellular immunity. Functional tests of cellular immunity play a critical role in several clinical scenarios. An excellent T cell response to vaccine antigens is arguably the best in vitro test of normal cellular immunity.

In this article the reference intervals for over 250 healthy adults were calculated for lectins, anti-CD3 (OKT3) and antigens comprising Candida, tetanus and diphtheria toxoids. These samples were provided by volunteer blood donors as controls to be run in parallel with diagnostic tests of in vitro cellular immunity in patients with suspected immunodeficiency.

The control samples uniformly responded to PHA. The response to other lectins, OKT3 and antigens was more heterogeneous. The variable responses to diphtheria and tetanus toxoids likely reflected the immunization status of these blood donors to these vaccine antigens.

Although there has been a recent move to implement non-radioactive methods for functional cellular immunity, 3H thymidine uptake continues to be utilized in many diagnostic laboratories because of excellent sensitivity. Robust vaccine-induced cellular responses in immunodeficient patients may inform clinical decisions such as using live attenuated viral vaccines. Similarly, markedly impaired responses to phytohemagglutinin A (PHA), in the appropriate clinical context, supports a diagnosis of Severe Combined Immunodeficiency (SCID) and the need for urgent hematopoietic stem cell transplantation (HSCT). The reference intervals established by this audit will assist other diagnostic laboratories using this platform.

© 2025 The Authors. Published by Elsevier B.V.