Lymphopenia and Severe Combined Immunodeficiency (SCID) - Think Before You Ink

Objectives Severe combined immunodeficiency (SCID) represents one of the most severe forms of Primary immunodeficiency (PID) disorders, characterized by T cell lymphopenia (TCL) and lack of cellular and humoral immune responses. However, not all patients with low T cell lymphocyte counts may have an abnormal T cell immunity and the observed TCL may be a temporary suppression resulting from transient lymphopenia secondary to severe infections. In such cases, it is necessary to estimate the severity of the observed TCL by assessing thymic capabilities. Methods In this study, patients clinically suspected of SCID were evaluated for lymphocyte subsets analysis, naïve T cells and T cell receptor excision circles (TREC). Results Patients with transient lymphopenia had detectable TREC levels and normal naïve T cells subsets. Normalization of absolute lymphocyte counts, and T cells was seen in the patients after a short duration. Conclusions The authors highlight the importance of detailed immunological investigations in an infant with severe infections and lymphopenia before labeling the infant as SCID.