Preventive Services Task Force and Evidence Based Prevention

The U.S. Preventive Services Task Force (USPSTF) is an independent panel of 16 private-sector experts in primary care, clinical prevention, and epidemiologic methodology

Table 6-1 World Health Organization Criteria for a Screening Test

1. The condition being screened for should be an important health problem.

2. The natural history of the condition should be well understood.

3. There should be a detectable early stage.

4. Treatment at an early stage should be of more benefit than at a later stage.

5. A suitable test should be devised for the early stage.

6. The test should be acceptable.

7. Intervals for repeating the test should be determined.

8. Adequate health service provision should be made for the extra clinical workload resulting from screening.

9. The physical and psychological risks should be less than the benefits.

10. The costs should be balanced against the benefits.

From Wilson JMG, Jungner G. Principles and Practice of Screening for Disease. Geneva, World Health Organization, 1968.

(Guirguis-Blake, 2007). The USPSTF addresses a broad array of prevention topics important to primary care practice, including cancer prevention. Their recommendations address primary and secondary preventive services performed in primary care settings or recognized in primary care settings and referred to specialists. The 16 experts come from the clinical fields of family medicine, general internal medicine, pediatrics, obstetrics and gynecology, preventive medicine, behavioral medicine, and nursing. The USPSTF releases recommendations on a variety of topics relevant to family medicine that address preventive services for children, adolescents, and adults, including pregnant women.

The purpose of the USPSTF is to provide evidence-based recommendations for the provision of preventive services to apparently healthy individuals in the primary care setting. Primary and secondary preventive services addressed by the USPSTF include screening, counseling, and preventive medications. The methodology of the USPSTF is rigorous and transparent and involves the following steps:

1. Creation of an analytic framework and key questions to determine the scope of the literature review.

2. Systematic review of all relevant literature answering the key questions.

3. Quality-rating bodies of literature supporting each key question.

4. Quantification of the magnitude of benefits and harms.

5. Balancing the net benefits and harms of a specific preventive service.

The recommendation is then linked to a letter grade that reflects the magnitude of net benefit (i.e., balance of benefits and harms) and the strength of the evidence supporting the provision of a specific preventive service (see Evidence-Based Summary).

Using screening for osteoporosis as an example, the task force created a set of key questions beginning with an overarching question: Does osteoporosis screening result in decreased mortality or disability from osteoporosis? Because no evidence directly answered this question, a chain of intermediate key questions was systematically searched. What is the accuracy of screening tests (e.g., dual-energy x-ray absorptiometry [DEXA] scans)? What is the effectiveness of treatment of these screen-detected cases in preventing osteoporosis-related fractures, fracture-specific mortality, or overall mortality? What harms are caused by screening for and treatment of osteoporosis (Figure 6-1)? For USPSTF to recommend screening, each link in the chain of evidence must be supported by evidence, and there must be fair- or good-quality evidence that the benefits outweigh the harms. Any break in the chain of evidence (e.g., single key question for which there is insufficient evidence) results in a conclusion of insufficient evidence for that preventive service.

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