Evidence Based Prevention Definitions

Prevention is often categorized as primary, secondary, and tertiary prevention. Primary prevention is defined as interventions that reduce the risk of disease occurrence in otherwise healthy individuals. Counseling patients to avoid smoking and prescribing fluoride to children to prevent cavities are examples of primary prevention. Secondary prevention includes screening to identify risk factors for disease or the early detection of a disease among asymptomatic and at-risk individuals. Evaluating and treating abnormal blood pressure in adults is an effective way to identify individuals at risk for heart disease and provides an opportunity to intervene before the disease occurs. Screening for colon cancer using colonoscopy to detect precancerous polyps and then removing the polyps is another example of secondary prevention. Individuals who receive primary or secondary prevention services have no obvious signs of illness; in clinical terms, they are asymptomatic.

In contrast, tertiary prevention services are provided to individuals who clearly have a disease, and the goal is to prevent them from developing further complications. For example, diabetes care, including regular retinal examinations, foot care, and management of blood sugar levels, is tertiary prevention because the care provided is focused on limiting the complications of a disease that has already been identified. Many believe tertiary prevention is outside the scope of traditional prevention and should be a part of disease management.

Because prevention involves an intervention in a patient who is asymptomatic, clinicians should demand a high standard of evidence that proposed prevention strategies, including screening, counseling, chemoprevention, and immunizations, have been proven to prevent disease. This is critical because all interventions, including preventive screenings and immunizations, have harms. Evidence-based prevention recognizes that doing something to healthy asymptomatic patients requires a good evidence base that the benefits of the intervention outweigh its harms. Benefits to patients should be improvements in patient-oriented outcomes—benefits that are meaningful to a patient's function and well-being—rather than in intermediate outcomes, such as improvements in laboratory test results.

Steps involved in systematically assessing the net benefit of a preventive service involve assessing the ability to detect a risk factor or early disease before it causes complications; understanding and quantifying the effectiveness of early identification to modify a risk factor or condition and early intervention (compared with waiting until the condition becomes clinically apparent); understanding and quantifying the harms that result from the preventive service, including those from additional confirmatory testing and treatment of the condition; and balancing the overall benefits and harms of this preventive service.

Preventive services also involve costs of time and money to the patient and the health care system. Even services such as counseling that, on face value, appear to require minimal cost, actually involve a considerable cost in time and personnel resources, especially for counseling services that require intensive and repeated multifaceted counseling sessions to be effective. The time and personnel costs of counseling interventions must be balanced against the cost savings resulting from prevention or delay of a costly chronic illness. A well-established set of criteria from the World Health Organization (WHO) can help in evaluating whether screening is appropriate for specific diseases (Table 6-1).

In general, evidence-based prevention involves evidence derived from populations, and what "works" for a population may or may not be appropriate for an individual patient. Often, the populations who choose to be a part of randomized, controlled trials and other clinical trials are carefully selected and monitored for adherence to treatments. At the same time, it is not feasible to do an N-of-1 trial for every patient who visits the clinic. When considering applying evidence-based prevention, like evidence-based medicine in general, it is important to ask if the evidence or guideline applies to the individual patient.

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