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 Red Blood Cells The main components of blood include Plasma Red blood cells White blood cells Platelets read more
and hemoglobin can cause symptoms of 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 , such as fatigue, weakness, and shortness of breath.Decreased white blood cells White Blood Cells The main components of blood include Plasma Red blood cells White blood cells Platelets read more
or immune system proteins Components 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 can cause recurrent fever and infections Fever in Adults Fever is an elevated body temperature that occurs when the body's thermostat (located in the hypothalamus in the brain) resets at a higher temperature, primarily in response to an infection... read more .Decreased platelets Platelets The main components of blood include Plasma Red blood cells White blood cells Platelets read more
or blood clotting factors 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 can cause abnormal bleeding and bruising Bruising and Bleeding Bruising or bleeding after an injury is normal (see also How Blood Clots). However, some people have disorders that cause them to bruise or bleed too easily. Sometimes people bleed without any... read more 
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Occasionally, symptoms may relate to increases in blood components.
Increased red blood cells (erythrocytosis Erythrocytosis Erythrocytosis is increased production of red blood cells (erythrocytes). (See also Overview of Myeloproliferative Neoplasms.) Erythrocytosis may be Primary: Caused by a disorder of the blood-forming... read more ) can cause thickening of the blood (increased blood viscosity) and thereby cause headache and a reddened or ruddy complexion (plethora).
Increased immune system proteins also can cause thickening of the blood (increased blood viscosity).
Increased platelets (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 ) or blood clotting factors can cause inappropriate excessive blood clotting (thrombosis).
When blood disorders cause a person's blood to become thickened, the thickened (more viscous) blood may have difficulty passing through small blood vessels, decreasing blood flow to certain areas of the body, which is a serious condition called hyperviscosity syndrome Hyperviscosity syndrome Neutrophilic leukocytosis is an abnormally high number of neutrophils (a type of white blood cell) in the blood. Neutrophils are a type of white blood cell that help the body fight infections... read more . Affected people may experience symptoms such as shortness of breath, headaches, dizziness, and confusion. Hyperviscosity syndrome can occur in people who have multiple myeloma Multiple Myeloma Multiple myeloma is a cancer of plasma cells in which abnormal plasma cells multiply uncontrollably in the bone marrow and occasionally in other parts of the body. People often have bone pain... read more , in which it is caused by increased immune system proteins.
Blood disorders often cause symptoms that can also occur in other disorders. For example, the weakness and shortness of breath caused by 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 can be caused by other conditions that impair oxygen delivery to the body, such as heart or lung disorders. Also, easy bruising Bruising and Bleeding Bruising or bleeding after an injury is normal (see also How Blood Clots). However, some people have disorders that cause them to bruise or bleed too easily. Sometimes people bleed without any... read more , a symptom suggestive of a blood disorder, can be caused by other conditions such as disorders of the blood vessels or the use of various drugs such as aspirin. Blood in the urine Blood in Urine Blood in the urine (hematuria) can make urine appear pink, red, or brown, depending on the amount of blood, how long it has been in the urine, and how acidic the urine is. An amount of blood... read more or stool Gastrointestinal Bleeding Bleeding may occur anywhere along the digestive (gastrointestinal or GI) tract, from the mouth to the anus. Blood may be easily seen by the naked eye (overt), or blood may be present in amounts... read more 
can be caused by a blood disorder but is usually caused by an abnormality in the urinary or gastrointestinal tract.
Although people may have bleeding after an injury or a medical procedure (such as dental procedures) or during menstruation, the presence of some blood disorders makes such bleeding worse.
Some symptoms are more suggestive of a blood disorder. Just a few examples include the following:
Blood clot 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 (phlebitis), usually in a leg (most often causing swelling, redness, and/or warmth of the leg or shortness of breath)
Petechiae (fine pin-point red, purple, or brown spots on skin or mucus membranes such as inner surface of the eyelids or in the mouth) caused by too few platelets 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
Blood blisters in the mouth (caused by too few platelets or clotting problems Bruising and Bleeding Bruising or bleeding after an injury is normal (see also How Blood Clots). However, some people have disorders that cause them to bruise or bleed too easily. Sometimes people bleed without any... read more
)Swollen lymph nodes Swollen Lymph Nodes Lymph nodes are tiny, bean-shaped organs that filter lymph fluid. They are located throughout the body, but particular collections are found just under the skin in the neck, under the arms,... read more
caused by white blood cell cancers (such as leukemias Overview of Leukemia Leukemias are cancers of white blood cells or of cells that develop into white blood cells. White blood cells develop from stem cells in the bone marrow. Sometimes the development goes awry... read more or lymphomas Overview of Lymphoma Lymphomas are cancers of lymphocytes, which reside in the lymphatic system and in blood-forming organs. Lymphomas are cancers of a specific type of white blood cells known as lymphocytes. These... read more 
)Pica Pica Pica is an eating disorder characterized by regularly eating things that are not food. Usually, what people with pica eat does not harm them, but sometimes what they eat causes complications... read more (eating of ice, dirt, or clay) suggests iron deficiency anemia Iron Deficiency Anemia Iron deficiency anemia results from low or depleted stores of iron, which is needed to produce red blood cells. Excessive bleeding is the most common cause. People may be weak, short of breath... read more
