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.
