Peripheral-blood cytopenia, an early indicator of inborn errors of immunity.

Inborn errors of immunity (IEI) are inherited monogenic disorders resulting in defective immune response. Non-infectious presentations are increasingly more apparent. Widely available, cost-effective early indicators are needed. Peripheral-blood cytopenia may be a presenting laboratory feature or an observed secondary phenomenon. This retrospective review of the South African Primary Immunodeficiency Registry (SAPIDR) aimed to assess the haematological indices at presentation and their association with the International Union of Immunological Societies (IUIS) 2019 IEI classification and mortality. Of 396 patients on the SAPIDR, 66% (n = 257) had available haematological results. Sixty percent were males and 85% under 18 years. A majority (53%) had predominantly antibody deficiency. At presentation, infection was prominent (86%) followed by cytopenia (62%). Neutropenia was associated with IUIS III [odds ratio (OR) 3.65, confidence interval (CI) 1.44-9.25], thrombocytopenia with IUIS II (OR 14.39, CI 2.89-71.57), lymphopenia with IUIS I (OR 12.16, CI 2.75-53.73) and pancytopenia with IUSI I (OR 12.24, CI 3.82-39.05) and IUIS II (OR 5.99, CI 2.80-12.76). Cytopenia showed shorter overall survival (OR 2.81, CI 1.288-4.16). Cytopenias that are severe, persistent, unusual and/or recurrent should prompt further investigation for IEI. The full blood count and leucocyte differential may facilitate earlier identification and serve as an adjunct to definitive molecular classification.