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Thick blood is caused by a variety of conditions, such as heavy proteins in the blood, too much blood in circulation or a blood clot system imbalance, according to Southeastern Medical Oncology Center. Diseases such as cancer and lupus can also lead to thick blood. Continue Reading.
An excess of platelets can cause excessive clotting or sometimes bleeding if the platelets are not functioning properly. However, people with too many platelets often have no signs or symptoms, so the condition may be found only when a platelet count is done as part of a health check or for other reasons.