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Thick blood may also be caused by the presence of harmful pathogens such as fungi, viruses, bacteria, and parasites. These pathogens can actually activate a coagulation response in the body as a way to avoid being attacked by the bodyâs immune system.
Thick blood is caused by heavy proteins, or by too much blood in the circulation. Too many red cells, white cells, and platelets will result in blood thickening. Another cause is an imbalance in the blood clotting system.