Common causes of thick blood include too many red blood cells or platelets and diseases such as lupus, according to Southeastern Medical Oncology Clinic. Polycythemia vera is a rare blood disease that leads to extra red blood cells, causing thick blood, notes the National Heart, Lung, and Blood Institute.
Lupus is an autoimmune condition caused by a variety of factors, including genetics, explains the National Institute of Arthritis and Musculoskeletal and Skin Diseases. The most common type of lupus is systemic lupus erythematosus, which affects many parts of the body. Symptoms of lupus are intermittent and can range from mild to severe. The most common symptoms include muscle pain, hair loss, mouth ulcers and pain in the joints. Less common symptoms, such as anemia, headaches, confusion and seizures, may also appear.
Polycythemia vera causes blood clots to form more easily, which can lead to complications such as heart attack or stroke, according to the National Heart, Lung, and Blood Institute. Because thick blood flows more slowly than normal blood, certain organs may not get enough oxygen, leading to angina and heart failure. A major cause of polycythemia vera is a genetic mutation, but other factors, such as long-term exposure to low oxygen levels, can also cause it. Symptoms of the disease, such as headaches, itching and blurred vision, may not appear for years.