[4][5] For these reasons, a test used in a screening program, especially for a disease with low incidence, must have good sensitivity in addition to acceptable specificity.
Case finding involves screening a smaller group of people based on the presence of risk factors (for example, because a family member has been diagnosed with a hereditary disease).
Frequently updated recommendations for screening are provided by the independent panel of experts, the United States Preventive Services Task Force.
[7] In 1968, the World Health Organization published guidelines on the Principles and practice of screening for disease, which is often referred to as the Wilson and Jungner criteria.
[8] The principles are still broadly applicable today: In 2008, with the emergence of new genomic technologies, the WHO synthesised and modified these with the new understanding as follows: Synthesis of emerging screening criteria proposed over the past 40 years In summation, "when it comes to the allocation of scarce resources, economic considerations must be considered alongside 'notions of justice, equity, personal freedom, political feasibility, and the constraints of current law'.
In some countries, such as the UK, policy is made nationally and programmes are delivered nationwide to uniform quality standards.
There are currently bills being introduced in various U.S. states to mandate mental health screenings for students attending public schools in hopes to prevent self-harm as well as the harming of peers.
[13] Screening is believed to a valuable tool in identifying patients' basic needs in a social determinants of health framework so that they can be better served.
[17][18] Several clinics across the United States have employed a system in which they screen patients for certain risk factors related to social determinants of health.
[15] Some programs, like the FIND Desk at UCSF Benioff Children's Hospital, employ screening for social determinants of health in order to connect their patients with social services and community resources that may provide patients greater autonomy and mobility.
[citation needed] Before a screening program is implemented, it should be looked at to ensure that putting it in place would do more good than harm.
[24] Autopsy studies have shown that between 14 and 77% of elderly men who have died of other causes are found to have had prostate cancer.
[28] Another example of overdiagnosis happened with thyroid cancer: its incidence tripled in United States between 1975 and 2009, while mortality was constant.
[31] The problem of overdiagnosis in cancer screening is that at the time of diagnosis it not possible to differentiate between a harmless lesion and lethal one, unless the patient is not treated and dies from other causes.
As researchers Welch and Black put it, "Overdiagnosis—along with the subsequent unneeded treatment with its attendant risks—is arguably the most important harm associated with early cancer detection.
If we do not think about what survival time actually means in this context, we might attribute success to a screening test that does nothing but advance diagnosis.
Screening is more likely to detect slower-growing tumors (due to longer pre-clinical sojourn time) that are less likely to cause harm.
The reason seems to be that people who are healthy, affluent, physically fit, non-smokers with long-lived parents are more likely to come and get screened than those on low-income, who have existing health and social problems.
[35] The best way to minimize selection bias is to use a randomized controlled trial, though observational, naturalistic, or retrospective studies can be of some value and are typically easier to conduct.
Such studies take a long time and are expensive, but can provide the most useful data with which to evaluate the screening program and practice evidence-based medicine.