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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.
Cells & protein: Blood may become too thick if there too many cells or too much protein. Increased red cell count, polycythemia, can make the blood viscous. High levels of immunogolobulins, usually due to cancer, also increse viscosity. Rarely leukemia with a very high white cell count may make the blood thick.