When to think of immunodeficiency?

Primary Immunodeficiencies (PIDs), although rare, are serious and heightened clinical suspicion leads to earlier diagnosis and improved outcome. Recognition of PIDs may be difficult as infections are common in young children in particular. Clues to the diagnosis of PID may be found in history, examination and initial basic investigations such as lymphocyte count. Age at presentation, type of infective organism and family history help focus on likely PIDs. Type of infective organism may indicate a specific PID, for example Aspergillus and Chronic Granulomatous Disease and Pneumocystis Jiroveci and SCID amongst others. Diagnostic aids such as 'The 10 Warning Signs of Primary Immunodeficiency' can be useful with failure to thrive, need for IV antibiotics, and family history of severe or unusual infections being the most discriminating. Systemic examination including the recognition of dysmorphic features may also support a particular diagnosis.