Genetic relatives of hereditary colorectal cancer patients with Lynch syndrome (LS) are at risk of cancer. Testing both colorectal cancer patients and relatives of mutation carriers for LS allows targeted prevention. However, this could mean disclosing sensitive health data to family members. In light of potential trade-offs between cost-effectiveness and patient privacy, this study investigates the implications of increasing test uptake in Germany. Out of 22 screening strategies for LS, the non-dominated and current German strategies were assessed from the perspective of the statutory health insurance. Life years gained by increased prevention were estimated with Markov models. The effects and implications of different test uptake rates in index patients and their relatives were investigated by scenario analysis. Privacy limitations could yield health gains of up to 2500 undiscounted life years for first-degree relatives of index patients and substantially improve cost-effectiveness. However, this approach may contradict the right to informational self-determination. This study demonstrates the effect higher LS test uptakes could have on the lives and rights of colorectal cancer patients and their relatives. It shows potential conflicts between the efficient use of health care resources on the one hand and reasonable consideration of patient autonomy on the other.