18 Clinical Preventive Services (United States Preventive Services Task Force)
In Chapter 16, we explored how screening is, in the most literal sense, “looking for trouble.” Looking for trouble makes sense if, by finding it early, it can be fixed. But if you don’t know what to do with the trouble you find, you are no longer just looking for trouble, you are asking for it.1 The credibility of preventive medicine depends on the following two goals:
The U.S. Preventive Services Task Force (USPSTF) was founded in 1984 to address these goals. This chapter focuses on why its work is important and how busy clinicians can keep up-to-date with and incorporate the Task Force’s recommendations. Recommendations for clinical preventive services change frequently with emerging evidence. For more details and updated recommendations, readers should consult USPSTF online (see Website list at end of chapter).
When the USPSTF was first convened by the U.S. Public Health Service in 1984, it was modeled on an earlier Canadian task force to serve as an independent panel of experts on prevention and evidence-based medicine (EBM). Since 1995, the Task Force has worked under the Agency of Healthcare Research and Quality (AHRQ). It covers all primary and secondary preventive services, including screening, counseling, and specific chemoprophylaxis.2 The Task Force aims to provide accurate and balanced recommendations across a spectrum of populations, types of services, and disease types. Its mission is to:
This mission is very circumscribed. The USPSTF only considers screening of asymptomatic patients, and it only deals with preventive services within primary care. Often, however, USPSTF recommendations are criticized by specialist organizations. Specialists may primarily see preselected patients with subtler symptoms that were missed earlier or may see high-risk groups. Screening decisions for such patients may be different from those for the general population, because the pretest probability of disease is much higher. On the other hand, recommendations of USPSTF are sometimes used for insurance decisions about which screening tests to cover. In these cases, recommendations may be more broadly applied than intended. In contrast to the Community Preventive Services Guide (see Chapter 26), the USPSTF does not take cost-effectiveness or financial concerns into consideration.
When the USPSTF was founded, its principles were revolutionary: that preventive care should be rigorously evaluated, and that not every screening test was worth doing. In its history, USPSTF has often recommended against or failed to endorse screening tests that were recommended by other organizations. The reason for this reluctance to endorse some interventions may be based on several assumptions of the Task Force.
As outlined in Chapter 16, screening studies are subject to many biases that lead researchers to overestimate benefits. Therefore the Task Force places a higher burden of evidence for benefits than for evidence of harm. For benefits, USPSTF will only accept evidence from randomized controlled trials (RCTs), community trials, meta-analyses, or systematic reviews. However, it will take into account evidence of cohort studies and case-control studies in calculations of harm.
Prevention studies describe the upper bounds of efficacy. In other words, controlled trials describe a best-case scenario with well-trained and highly motivated providers and patients. The Task Force assumes that in the real world, with unselected providers and in the general population, the effectiveness of a screening program will be lower.
Delivery of a screening service is not an outcome. Diagnosis of a disease also is not an outcome. Therefore the benefit of a screening program lies not in the number of patients screened or the number of patients diagnosed with disease, but only in the health outcomes. Health outcomes are changes in a patient’s health or health perception, such as pain, shortness of breath, or death. In contrast to health outcomes, intermediate outcomes are measurements of pathology or physiology that can lead to health outcomes (e.g., high blood pressure). USPSTF will give no weight to evidence of number of screening events or cases found, and it gives greater weight to studies of health outcomes than to those of intermediate outcomes.
Because the standard for evidence is so high, USPSTF may wait longer than other organizations before endorsing screening modalities, as with lung cancer screening using helical computed tomography (CT). The number of patient lives potentially saved must be weighed against the risk of subjecting healthy patients to potentially harmful screening tests. With this tension and when in doubt, the Task Force seems to prefer being late to being wrong.
Developing a recommendation is a two-part process: reviewing the evidence and formulating recommendations. Although the Task Force itself makes the recommendations, independent centers review the evidence. USPSTF has established 12 such evidence-based practice centers (EPCs).3 The literature review and recommendation process is highly structured and includes various steps to safeguard the Task Force’s integrity and to help it pursue its goals of transparency, accountability, consistency, and independence4 (Table 18-1). Safeguards include stringent criteria for selection of members, stringent policies regarding conflict of interest, dual review of each abstract, and a comment period for community partners and the public.
Sixteen members serve on the Task Force at any given time. About 25% of USPSTF members are replaced each year. Members are nominated in a public process and are chosen based on their expertise in the subject matter, research methods, disease prevention, application of synthesized evidence to clinical decision making, and clinical expertise in primary health care. They are chosen through a rigorous process and serve staggered 4-year terms on the committee.
Once Task Force members have answered these questions, the group assigns a grade for the service of A, B, C, D, or I5 (Table 18-2). After assigning a tentative grade, the Task Force discusses these recommendations with federal and primary care partners. Federal partners include the Centers for Disease Control and Prevention (CDC), Center for Medicare and Medicaid Services (CMS), Health Resource and Services Administration (HRSA), National Institutes of Health (NIH), and Food and Drug Administration (FDA). Examples of primary care partners include the American Medical Association, American College of Physicians, and American College of Preventive Medicine.