What are the core assumptions underlying screening programs, and how do they relate to the criteria for implementing a screening program?

The core assumptions are that screening will reduce disease-associated morbidity and mortality through early identification and treatment, and that all who screen positive have access to appropriate assessment and treatment services. These assumptions underpin the screening criteria: valid tests, practical tests, serious disease, effective early treatment, high prevalence, and available referral resources. Each criterion helps ensure the assumptions can actually be met in practice.

The text identifies two core assumptions underlying screening programs. First, screening is assumed to reduce disease-associated morbidity and mortality because it allows early identification and early engagement in treatment. Second, it is assumed that everyone who screens positive for probable disease has access to appropriate assessment and treatment services. These assumptions are the basis for deciding whether a screening program should be implemented. For example, the criterion that the disease be serious enough to warrant screening and that early treatment be more effective directly supports the first assumption: if early detection does not lead to better outcomes, screening will not reduce morbidity or mortality. The criterion that resources are available for referral, diagnosis, and treatment supports the second assumption: without economic access, physical access, and capacity to treat, positive screens cannot receive the follow-up care they need. Other criteria, such as high sensitivity and specificity, simplicity and acceptability of the test, and high prevalence in the target population, also serve to make the screening program effective and ethically sound. The text stresses that it is unethical to conduct screening if treatment is not available, because the program would fail to fulfill its core assumption of reducing harm.