Comprehensive approach to primary immunodeficiencies in adulthood: recognition and diagnosis.

Primary immunodeficiencies, now referred to as inborn errors of immunity (IEI), are increasingly recognized in adults, not only in the pediatric population. In adults, they may present with recurrent, severe, or unusual infections, but also with autoimmunity, malignancy, allergies, or inflammation, posing a diagnostic challenge. This review is based on clinical experience and the 2022 International Union of Immunological Societies classification. It includes four clinical cases and proposes a practical approach for the evaluation of adults. In the presence of suspected IEI, a stepwise laboratory approach is proposed to facilitate early detection and improve prognosis. Initial screening with basic immunological tests-including complete blood count, immunoglobulin and complement levels, and lymphocyte immunophenotyping-is emphasized. Confirmation of each IEI requires more specific testing, often involving molecular techniques.