Population screening aims to detect disease before symptoms arise, shifting intervention earlier in the disease pathway. However, screening is not inherently beneficial; it requires careful evaluation of evidence, test accuracy, disease prevalence, and potential harms.
This chapter examines principles of screening, including sensitivity, specificity, predictive values, overdiagnosis, lead-time bias, and cost-effectiveness. It reviews established screening programmes such as breast, cervical, and colorectal cancer, as well as emerging technologies.
Screening is framed as a calibrated intervention - powerful when appropriately applied, harmful when misused. Public health must balance early detection with ethical stewardship, ensuring programmes are evidence-based, equitable, and proportionate.
Detection without discernment risks unintended consequence.
Key Takeaways
Screening targets asymptomatic populations to detect early disease.
Test performance depends on sensitivity, specificity, and prevalence.
Overdiagnosis and false positives carry psychological and clinical consequences.
Screening must meet established criteria before implementation.
Equity and access are central to screening effectiveness.
Ongoing evaluation is essential for programme sustainability.
Screening is prevention only when benefit outweighs harm.
