Abstract
Immunodeficiency occurs when one or more immune system components do not function properly, resulting in the body's inability to resist mostly infectious agents. Most cases of immunodeficiency in adults are acquired (secondary), but congenital immunodeficiencies are not uncommon. Primary immunodeficiencies are a heterogeneous group of innate immune errors that result in various clinical and laboratory manifestations. In contrast, secondary immunodeficiencies involve an acquired decrease in immune cell count and/or impairment of their function, commonly associated with an antibody level decrease. Secondary immunodeficiency in patients with B-cell hematological malignancies is a common condition attributed to both hematological malignancy and secondary antitumor therapy-related causes. Paradoxically, immunodeficiency, initially attributed to secondary causes, may be due to a previously undiagnosed primary immunodeficiency. Early diagnosis of immunodeficiency and optimization of management strategies with a multidisciplinary approach are critical to providing the most effective specific treatments and reducing the incidence of infection-related complications and mortality. The article addresses clinical practice, recommendations, and problems of immunodeficiency diagnosis and the effectiveness of immunoglobulin replacement therapy illustrated by clinical cases.