Introduction

Blood consists of a liquid (plasma) that contains red blood cells, white blood cells, platelets, and other components. A blood disorder can develop when there are too many or too few of these components or when they are abnormal.

Each component of the blood has an important function. Red blood cells (erythrocytes) carry oxygen to the body's tissues and carry carbon dioxide (a waste product) from the tissues. If there is a problem with red blood cells, the body's tissues do not get enough oxygen, and tissues and organs may malfunction. People with too few red blood cells (anemia) often feel tired. White blood cells (leukocytes) help fight infection and cancer. If there is a problem with white blood cells, infections and cancer are more likely to develop. Platelets (thrombocytes) and clotting factors help blood clot. If there is a problem with platelets or clotting factors, excessive bleeding or excessive clotting may occur. The inner part of bone (bone marrow) contains immature, unspecialized cells, called stem cells, that develop into white blood cells, red blood cells, or platelets. If there is a problem with bone marrow, too many or too few of these components may be produced.

Some blood disorders are more common among older people. However, sometimes blood disorders are not detected promptly because the symptoms, such as weakness, fatigue, and shortness of breath, are mistakenly attributed to aging itself. Certain cancers that affect the blood's components, such as multiple myeloma and leukemia, are relatively common among older people.