Characteristics of a Good Health Screening Test

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Health screening tests are an important part of medical care. Screening can take the form of simple questionnaires, lab tests, radiology exams (e.g. ultrasound, X-ray) or procedures (e.g. stress test). But just because a test is offered for screening purposes, it doesn't mean that it is a good screening test. Technical accuracy is necessary but not sufficient for a screening test. A combination of the right test, disease, patient and treatment plan makes up a health screening program.

Diagnostic vs. screening exam

A medical exam can be done for diagnostic or screening purposes, depending on whether the patient has signs or symptoms related to the disease in question. 

The purpose of a diagnostic medical exam is to establish the presence or absence of disease in an individual with signs or symptoms of the disease. A diagnostic test can also be done to follow up a positive screening test. The following are examples of diagnostic tests:

  • Cardiac stress test to look for heart disease in a person with chest pain
  • Chest X-ray to look for pneumonia in a person with a cough and fever
  • Complete blood count to look for anemia in a person with fatigue
  • Breast biopsy in a person with an abnormal screening mammogram

The purpose of a screening exam is to detect a disease before signs or symptoms appear in order to allow early treatment. The following are examples of screening tests endorsed by the U.S.

Preventive Services Task Force:

  • Colonoscopy, sigmoidoscopy, or stool test to detect colorectal cancer in adults 50 years or older who don't have signs or symptoms of the disease.
  • HIV test in adolescents and adults aged 15 to 65 years who don't have signs or symptoms of HIV.
  • Testing for type 2 diabetes in asymptomatic adults with sustained blood pressure (either treated or untreated) greater than 135/80 mm Hg
  • Testing for sickle cell disease in newborns

Screening tests are constantly being improved to increase their level of protection. For example, in the case of cervical cancer—which is caused by the human papillomavirus (HPV)—early detection can now be supported by the conventional Pap test screening as well as HPV DNA testing. Recent study results show that HPV testing is more sensitive. Many experts, therefore, argue that it should become the primary screening technology.

What makes a good screening test?

Just because we have a sophisticated test to detect a disease or abnormality, that doesn't mean the test is suitable for screening. For example, a whole-body imaging scan will detect abnormalities in the vast majority of individuals, but it is not recommended as a screening exam for people who are in good health. An exam is only appropriate for screening if it is done in the proper context, which involves questions about the disease itself, people who are susceptible to the disease, and available treatments.

Wilson and Jungner described criteria for a good screening program in their landmark 1968 paper. The World Health Organization adopted these 10 criteria that still serve as the foundation for much of the discussion surrounding screening programs today.

  1. The condition sought should be an important health problem.
  2. There should be an accepted treatment for patients with recognized disease.
  3. Facilities for diagnosis and treatment should be available.
  4. There should be a recognizable latent or early symptomatic stage.
  5. There should be a suitable test or examination.
  6. The test should be acceptable to the population.
  7. The natural history of the condition, including development from latent to declared disease, should be adequately understood.
  8. There should be an agreed policy on whom to treat as patients.
  9. The cost of case-finding (including diagnosis and treatment of patients diagnosed) should be economically balanced in relation to possible expenditure on medical care as a whole.
  1. Case-finding should be a continuing process and not a “once and for all” project

Note that the above criteria do not focus on the test itself, but rather the context in which it is used. If even one of the criteria is not met, then the chances are low that a given screening test will improve the health of our population.

Evolution of screening criteria

Wilson and Jungner did not intend their proposed criteria to be the final answer, but rather to stimulate further discussion. Technology continues to advance, allowing us to detect more and more diseases at a very early stage. But detection of a disease or abnormality doesn't always improve health. (For example, what is the benefit of screening for a disease if there is no treatment for it?) Refined screening criteria have been proposed that would account for the complexities of health care today.

Genetic screening is also becoming an important area of progress, including prenatal screening. Numerous genetic tests are now available, and primary care professionals need to be able to advise their patients so they can make informed choices. Some experts warn that genetic tests should not be routinized. Patients need to be aware of the benefits and risks before taking them. Furthermore, individuals with a high risk of developing a certain genetic condition might benefit just as much from addressing other components of their health, such as nutrition, environmental factors and exercise.

A crucial question to ask before accepting any test for screening purposes is "Does the screening test lead to overall better health?"

Sources

Anne Andermann et al. Revisiting Wilson and Jungner in the genomic age: a review of screening criteria over the past 40 years. Bulletin of the World Health Organization 2008; 86 (4):241-320.

Harris R et al. Reconsidering the Criteria for Evaluating Proposed Screening Programs: Reflections From 4 Current and Former Members of the U.S. Preventive Services Task Force. Epidemiol Rev (2011) 33 (1): 20-35.

Tota J, Bentley J, Ratnam S, et al. Introduction of molecular HPV testing as the primary technology in cervical cancer screening: Acting on evidence to change the current paradigm. Preventive Medicine, 2017;98 (Special Issue: Emerging Paradigms in Cervical Cancer Screening):5-14.

U.S. Preventive Services Task Force. USPSTF A and B Recommendations. Wilson JMG and Jungner G. Principles and practice of screening for disease. Public Health Papers No. 34. Geneva: World Health Organization; 1968.

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