Chapter 004. Screening and Prevention of Disease (Kỳ 1) pptx

Screening and Prevention of Disease Screening and Prevention of Disease: Introduction A primary goal of health care is to prevent disease or to detect it early enough that intervention

Chapter 004 Screening and Prevention of Disease

(Kỳ 1)

Harrison's Internal Medicine > Chapter 4 Screening and Prevention of

Disease

Screening and Prevention of Disease: Introduction

A primary goal of health care is to prevent disease or to detect it early enough that intervention will be more effective Strategies for disease screening and prevention are driven by evidence that testing and intervention are practical and effective Currently most screening tests are readily available and inexpensive Examples include tests that are biochemical (e.g., cholesterol, glucose), physiologic (e.g., blood pressure, growth curves), radiologic (e.g., mammogram, bone densitometry), or tissue specimens (e.g., Pap smear, fine-needle aspirations)

In the future, it is anticipated that genetic testing will play an increasingly important role for predicting disease risk (Chap 64) However, such tests are not widely used except for individuals at risk for high-penetrance genes based on

family or ethnic history (e.g., BRCA1, BRCA2) The identification of

low-penetrance but high-frequency genes that cause common disorders such as diabetes, hypertension, or macular degeneration offers the possibility of new genetic tests However, any new screening test, whether based on genetic or other methods, must be subjected to rigorous evaluation of its sensitivity, specificity, impact on disease, and cost-effectiveness Physicians and patients are continuously introduced to new screening tests, often in advance of complete evaluation For example, the use of whole-body CT imaging has been advocated as a means to screen for a variety of disorders Though appealing in concept, there is currently

no evidence to justify this approach, which is associated with high cost and a substantial risk of false-positive results

This chapter will review the basic principles of screening and prevention in the primary care setting Recommendations for specific disorders, such as cardiovascular disease, diabetes, or cancer, are provided in the chapters dedicated

to these topics

Basic Principles of Screening

In general, screening is most effective when applied to relatively common disorders that carry a large disease burden (Table 4-1) The five leading causes of mortality in the United States are heart diseases, malignant neoplasms, accidents, cerebrovascular diseases, and chronic obstructive pulmonary disease Thus, many prevention strategies are targeted at these conditions From a global health perspective, these same conditions are priorities, but malaria, malnutrition, AIDS, tuberculosis, and violence carry a heavy disease burden (Chap 2)

Table 4-1 Lifetime Cumulative Risk

Breast cancer for women 10%

Colon cancer 6%

Cancer of the cervix for womena

2%

Domestic violence for women Up to 15%

Hip fracture for Caucasian women 16%

Assuming an unscreened population

A primary goal of screening is the early detection of a risk factor or disease

at a stage when it can be corrected or cured For example, most cancers have a better prognosis when identified as premalignant lesions or when they are still resectable Similarly, early identification of hypertension or hyperlipidemia allows therapeutic interventions that reduce the long-term risk of cardiovascular or cerebrovascular events However, early detection does not necessarily influence survival For example, in some studies of lung cancer screening, tumors are identified at an earlier stage, but overall mortality does not differ between screened and unscreened populations The apparent improvement in 5-year survival rates can be attributed to the detection of smaller tumors rather than a real change in clinical course after diagnosis Similarly, the detection of prostate cancer may not lead to a mortality difference because the disease is often indolent and competing morbidities, such as coronary artery disease, may ultimately cause mortality (Chap 78)

Disorders with a long latency period increase the potential gains associated with detection For example, cancer of the cervix has a long latency between dysplasia and invasive carcinoma, providing an opportunity for detection by routine screening It is hoped that the introduction of new papilloma virus vaccines will provide additional disease prevention, ultimately reducing the reliance on

screening for cervical cancer For colon cancer, an adenomatous polyp progresses

to invasive cancer over 4–12 years, providing an opportunity to detect early lesions by fecal occult blood testing (FOBT) or endoscopy On the other hand, breast cancer screening in premenopausal women is more challenging because of the relatively short interval between development of a localized breast cancer and metastasis to regional nodes (estimated to be ~12 months)