Which factors that can cause a false positive hepatitis c test?

Autoimmune: No test is perfect. Every test has a false positive and false negative rate. Any condition that leads to lots of antibody production, like autoimmune diseases, can lead to false positive tests. In hcv, antibody response is not as important as viral load since about 25% of people will be truly infected but clear it themselves. Everyone with hcv antibodies needs an hcv RNA test for active infection.