How to investigate a suspected immune deficiency in adults.

Patients with immune deficiencies can present with variable clinical phenotypes. This often translates into a significant delay in their diagnosis, and resultant patient morbidity. This review summarises the most common types of immunodeficiency disorders, primary and secondary, along with their key features. It provides a structured approach for the clinician on when to suspect an immunodeficiency, the initial investigations pathway and when a specialist referral should be considered.