Secondary prevention as a complex adaptive system: risk classification, healthcare capacity, and inequality

In many health systems, secondary prevention operates as a routine infrastructure of adult healthcare. Guideline thresholds help determine who is classified as at risk and who enters ongoing monitoring and treatment, yet they produce system-wide consequences that are rarely considered together. Here we argue that viewing secondary prevention as a complex adaptive system helps connect debates on threshold shifts, overdiagnosis, healthcare demand and inequalities in preventive care. Using hypertension and statin eligibility as examples, we show how threshold shifts act as system-level events whose consequences extend beyond individual eligibility decisions. Characteristic features of complex adaptive systems, including feedback, adaptation, and nonlinearity, can interact with unequal access to shape preventive trajectories, generating pressure on finite healthcare capacity and inequalities in care and health outcomes. This systems perspective can help anticipate the unintended consequences of threshold changes and inform equitable approaches to preventive care.