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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: Common Causes. Certain ethnic races (particularly Caucasian) may have a genetic predisposition towards thick blood. Defects in the coagulation genes adversely affect the capability of the body to turn off the switch that activates the clotting process.