INTRODUCTION

Immune deficiency most often comes to clinical attention because of an increase in the incidence or severity of infectious illness beyond what is considered "normal." This topic review will provide a general approach to the laboratory evaluation of the immune system, beginning with screening tests and progressing through the indications for more advanced immunologic testing. Indications for referral to a specialist are discussed, and links to more detailed topics about the different groups of disorders are provided here and throughout the topic. (See "Primary humoral immune deficiencies: An overview" and "Combined immunodeficiencies" and "Primary disorders of phagocytic function: An overview" and "Laboratory evaluation of neutropenia and neutrophil dysfunction" and "Overview and clinical assessment of the complement system".)

INITIAL APPROACH TO THE PATIENT

Immune deficiency disorders should be considered once the more common causes of recurrent infection have been excluded. The initial approach to a child or adult with recurrent infections is described separately. (See "Approach to the child with recurrent infections" and "Approach to the adult with recurrent infections".)

Immune dysregulation can result in disorders other than recurrent infections, including:

• Autoimmune disorders, such as autoimmune hemolytic anemia
• Inflammatory disorders, such as inflammatory bowel disease or inflammatory arthritis
• Malignancies, such as lymphoma
• Allergic disease, such as atopic dermatitis, food allergy, and allergic rhinosinusitis and asthma

Before initiating immunologic testing, the clinician should perform a thorough clinical history and physical examination. In infants and children, height and weight records should be reviewed, as failure to thrive and poor growth are consistent with immunodeficiency. In patients with possible immunodeficiency, important elements of the clinical presentation include: