There are a number of types and causes of anemia that affect intensive care unit (ICU) patients, and the initial workup for this condition is important in correcting the underlying dysfunction. For example, the ICU patient may present with acute blood loss from a bleeding duodenal ulcer or diverticulosis. In this case, the administration of packed red blood cell transfusions and the treatment of the underlying cause are of importance. If, for example, the patient had a malignancy such as lymphoma, the anemia may result from an overcrowded marrow and insufficient erythrocyte production. Understanding the context of the anemia will not only allow for appropriate therapy and the correction of any underlying oxygen deficits, but will also provide an opportunity to appropriately treat the underlying condition.