Assessing Mechanisms Accounting for Unexplained Anemia in the Elderly

Background: \- Anemia occurs commonly and is associated with poor outcomes in the elderly. In about a third of anemia cases in older people (over age 65), the cause of anemia is unexplained. Anemia in older adults may be caused by the bone marrow's inability to produce red blood cells fast enough to replace older red blood cells that have died. Researchers want to look at unexplained anemia by studying the life span of red blood cells in younger adults and older adults. To do so, a vitamin called Biotin will be used as a marker on the red blood cells. Objectives: \- To investigate possible causes of unexplained anemia in older people. Eligibility: * Individuals in the following groups: * Men and women between 18 and 50 years of age who do not have anemia * Men and women at least 70 years of age who do not have anemia. * Men and women at least 70 years of age who have iron-deficiency anemia. * Men and women at least 70 years of age who have anemia with no known cause. Design: * Participants will be screened with a physical exam and medical history. Blood and urine samples will be collected. * Participants will have an overnight stay for the first study visit. They will provide a blood sample to which Biotin will be added. The blood sample with Biotin will then be returned to the participant. Twenty-four hours later, another blood sample will be collected. * Participants will have up to 14 additional study visits. At each visit, blood samples will be collected to measure the amount of Biotin remaining in the blood. * Participants may also provide a separate blood sample for genetic testing. These tests may provide more information about genetic causes of unexplained anemia.