Disorders that affect the blood are called blood disorders or hematologic disorders. There are many blood disorders, and they can affect the quantity as well as the function of the cells in the blood (blood cells) or proteins in the blood clotting system How Blood Clots Hemostasis is the body's way of stopping injured blood vessels from bleeding. Hemostasis includes clotting of the blood. Too little clotting can cause excessive bleeding from minor injury Too... read more or immune system Overview of the Immune System The immune system is designed to defend the body against foreign or dangerous invaders. Such invaders include Microorganisms (commonly called germs, such as bacteria, viruses, and fungi) Parasites... read more .
Some blood disorders cause the number of cells in the blood to decrease:
A decreased number of red blood cells Red Blood Cells The main components of blood include Plasma Red blood cells White blood cells Platelets read more
is called anemia Overview of Anemia Anemia is a condition in which the number of red blood cells is low. Red blood cells contain hemoglobin, a protein that enables them to carry oxygen from the lungs and deliver it to all parts... read more .A decreased number of white blood cells White Blood Cells The main components of blood include Plasma Red blood cells White blood cells Platelets read more
is called leukopenia Overview of White Blood Cell Disorders White blood cells (leukocytes) are an important part of the body’s defense against infectious organisms and foreign substances ( the immune system). To defend the body adequately, a sufficient... read more 
.A decreased number of platelets Platelets The main components of blood include Plasma Red blood cells White blood cells Platelets read more
is called thrombocytopenia Overview of Thrombocytopenia Thrombocytopenia is a low number of platelets (thrombocytes) in the blood, which increases the risk of bleeding. Thrombocytopenia occurs when the bone marrow makes too few platelets or when... read more 
.
Other blood disorders cause the numbers of blood cells to increase:
An increased number of white blood cells is called leukocytosis Overview of White Blood Cell Disorders White blood cells (leukocytes) are an important part of the body’s defense against infectious organisms and foreign substances ( the immune system). To defend the body adequately, a sufficient... read more
.An increased number of platelets is called thrombocytosis or thrombocythemia Essential Thrombocythemia Essential thrombocythemia is a myeloproliferative neoplasm in which excess platelets are produced, leading to abnormal blood clotting or bleeding. The hands and feet may burn, turn red, and... read more .
Other blood disorders affect proteins within the blood cells or blood plasma Plasma The main components of blood include Plasma Red blood cells White blood cells Platelets read more (the liquid portion of the blood):
Hemoglobin, the oxygen-carrying protein inside red blood cells
Immune system proteins, such as antibodies Overview of the Immune System The immune system is designed to defend the body against foreign or dangerous invaders. Such invaders include Microorganisms (commonly called germs, such as bacteria, viruses, and fungi) Parasites... read more (also called immunoglobulins)
Blood flows to every cell in the body and is important to the health and function of all of the body's organs.
Blood cells are produced in the bone marrow, and many blood proteins are made in the liver or the blood cells themselves. Blood cells and blood proteins provide the following functions:
Red blood cells contain hemoglobin, which carries oxygen to every part of the body.
White blood cells and antibodies fight infections and cancers.
Platelets and blood clotting factors make bleeding stop or prevent bleeding from occurring.
Blood disorders cause symptoms Symptoms of Blood Disorders Blood disorders can cause various symptoms in almost any area of the body. Most commonly, symptoms are caused by decreases in the blood components. Decreased red blood cells and hemoglobin can... read more 
resulting from disruption of these functions, and symptoms can arise from any tissues and organs that are adversely affected.
Doctors will ask about a person's symptoms and do a physical examination Medical History and Physical Examination for Blood Disorders Doctors first take a person's medical history (ask about symptoms, occupational or other exposures, and family information). Then they do a physical examination. The findings from the history... read more 
, but often, the presence of a blood disorder is first discovered by a blood test Complete blood count Doctors select tests to help diagnose blood disorders based on the person's symptoms and the results of the physical examination. Sometimes a blood disorder causes no symptoms but is discovered... read more such as the complete blood count (CBC) done when the doctor is doing a complete evaluation of a person or when investigating why a person is not feeling well. The doctor usually must do further blood tests to diagnose a person's blood disorder, and sometimes a bone marrow biopsy Bone Marrow Examination Red blood cells, most white blood cells, and platelets are produced in the bone marrow, the soft fatty tissue inside bone cavities. Sometimes a sample of bone marrow must be examined to determine... read more is necessary.
