Many patients in the Intensive Care Unit (ICU) are immunocompromised. In some, immunosuppression is easily apparent, especially when caused directly by underlying disease (such as hematological malignancies) or treatment (such as drugs to prevent organ rejection or as a side effect of cancer chemotherapy). In others, immunosuppression is less apparent and is induced by the underlying disease, for example following traumatic injury or sepsis, or as a response to therapies provided during intensive care (such as steroids).

Note: Infection remains an important cause of morbidity and mortality in immunocompromised patients.

While immunosuppression itself does not cause pathology, it does leave the patient more prone to infection. The clinician must maintain a high index of suspicion as there is currently no good test to measure the degree of immunosuppression. The consequences of immune suppression in the ICU highlight the importance of infection prevention and control, as well as surveillance measures to ensure that appropriate treatment is implemented safely and quickly. Intensive care clinicians require a thorough understanding of the mechanisms of immune suppression and the management of patients with immune dysfunction.