In medicine, screening is a strategy used to test for as-yet-unrecognised conditions or risk markers in individuals or populations without symptoms or signs of the disease being screened.
Screening interventions are designed to identify conditions which could at some future point turn into disease, thus enabling earlier intervention and management in the hope to reduce mortality and suffering from a disease. Although screening may lead to an earlier diagnosis, not all screening tests have been shown to benefit the person being screened- overdiagnosis, misdiagnosis, and creating a false sense of security are some potential adverse effects of screening. Additionally, some screening tests can be inappropriately overused. 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.
Several types of screening exist: universal (population-based) screening involves testing of all individuals in a certain category (for example, all children of a certain age). Case finding involves testing 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). When delivered to large numbers of people at the population level rather than by individual clinicians, testing asymptomatic people for disease because they have one or more risk factors is sometimes referred to as targeted or stratified screening. Screening interventions are not designed to be diagnostic, and often have significant rates of both false positive and false negative results.
In the US, frequently updated recommendations for screening are provided by the independent panel of experts, the United States Preventive Services Task Force. In the UK, recommendations are provided by the UK National Screening Committee.
Principles
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. The principles are still broadly applicable today:
The condition should be an important health problem. There should be a treatment for the condition. Facilities for diagnosis and treatment should be available. There should be a latent stage of the disease. There should be a test or examination for the condition. The test should be acceptable to the population. The natural history of the disease should be adequately understood. There should be an agreed policy on whom to treat. The total cost of finding a case should be economically balanced in relation to medical expenditure as a whole. Case-finding should be a continuous process, not just a "once and for all" project.
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 The screening programme should respond to a recognized need. The objectives of screening should be defined at the outset. There should be a defined target population. There should be scientific evidence of screening programme effectiveness. The programme should integrate education, testing, clinical services and programme management. There should be quality assurance, with mechanisms to minimize potential risks of screening. The programme should ensure informed consent, confidentiality and respect for personal, bodily autonomy. The programme should promote equity and access to screening for the entire target population. Programme evaluation should be planned from the outset. The overall benefits of screening should outweigh the harm. 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'."Anne Andermann, Ingeborg Blancquaert, Sylvie Beauchamp, Véronique Déry 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 Volume 86, Number 4, April 2008, 241-320
Types
Mass screening (sometimes termed population-based screening): The screening of a whole population or subgroup. It is offered to all, irrespective of the risk status of the individual. High risk or targeted screening or selective screening: High risk screening is conducted only among high-risk people. Multiphasic screening: The application of two or more screening tests to a large population at one time, instead of carrying out separate screening tests for single diseases. When done thoughtfully and based on research, identification of risk factors can be a strategy for medical screening.
Examples
Common programs In many countries there are population-based screening programmes. In some countries, such as the UK, policy is made nationally and programmes are delivered nationwide to uniform quality standards. Common screening programmes include: Cancer screening Pap smear or liquid-based cytology to detect potentially precancerous lesions and prevent cervical cancer Mammography to detect breast cancer Colonoscopy and fecal occult blood test to detect colorectal cancer Dermatological check to detect melanoma PSA to detect prostate cancer PPD test to screen for exposure to tuberculosis Beck Depression Inventory to screen for depression SPAI-B, the Liebowitz Social Anxiety Scale and Social Phobia Inventory to screen for social anxiety disorder Alpha-fetoprotein, blood tests and ultrasound scans for pregnant women to detect fetal abnormalities Bitewing radiographs to screen for interproximal dental caries Ophthalmoscopy or digital photography and image grading for diabetic retinopathy Ultrasound scan for abdominal aortic aneurysm SARI Screening Tool for COVID-19 and MERS Screening of potential sperm bank donors Screening for metabolic syndrome Screening for potential hearing loss in newborns Hearing screening at occupational health programs
School-based Most public school systems in the United States screen students periodically for hearing and vision deficiencies and dental problems. Screening for spinal and posture issues such as scoliosis is sometimes carried out, but is controversial as scoliosis (unlike vision or dental issues) is found in only a very small segment of the general population and because students must remove their shirts for screening. Many states no longer mandate scoliosis screenings, or allow them to be waived with parental notification. 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. Those proposing these bills hope to diagnose and treat mental illnesses such as depression and anxiety.
Screening for social determinants of health The social determinants of health are the economic and social conditions that influence individual and group differences in health status.Braveman, P. and Gottlieb, L., 2014. The social determinants of health: it's time to consider the causes of the causes. Public health reports, 129(1_suppl2), pp.19-31. Those conditions may have adverse effects on their health and well-being. To mitigate those adverse effects, certain health policies like the United States Affordable Care Act (2010) gave increased traction to preventive programs, such as those that routinely screen for social determinants of health.Heiman, Harry J., and Samantha Artiga. "Beyond Health Care: The Role of Social Determinants in Promoting Health and Health Equity." Health 20.10 (2015): 1-10. 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.Shekarchi, Amy, et al. "Social Determinant of Health Screening in a Safety Net Pediatric Primary Care Clinic." American Academy of Pediatrics, American Academy of Pediatrics, 1 May 2018, pediatrics.aappublications.org/content/142/1_MeetingAbstract/748.
Policy background in the United States When established in the United States, the Affordable Care Act was able to bridge the gap between community-based health and healthcare as a medical treatment, leading to programs that screened for social determinants of health. The Affordable Care Act established several services with an eye for social determinants or an openness to more diverse clientele, such as Community Transformation Grants, which were delegated to the community in order to establish "preventive community health activities" and "address health disparities".
Clinical programs Social determinants of health include social status, gender, ethnicity, economic status, education level, access to services, education, immigrant status, upbringing, and much, much more. 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. In such cases, it is done as a preventive measure in order to mitigate any detrimental effects of prolonged exposure to certain risk factors, or to simply begin remedying the adverse effects already faced by certain individuals. They can be structured in different ways, for example, online or in person, and yield different outcomes based on the patient's responses. 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.
Medical equipment used Medical equipment used in screening tests is usually different from equipment used in diagnostic tests as screening tests are used to indicate the likely presence or absence of a disease or condition in people not presenting symptoms; while diagnostic medical equipment is used to make quantitative physiological measurements to confirm and determine the progress of a suspected disease or condition. Medical screening equipment must be capable of fast processing of many cases, but may not need to be as precise as diagnostic equipment.
Limitations Screening can detect medical conditions at an early stage before symptoms present while treatment is more effective than for later detection. In the best of cases lives are saved. Like any medical test, the tests used in screening are not perfect. The test result may incorrectly show positive for those without disease (false positive), or negative for people who have the condition (false negative). Limitations of screening programmes can include: Screening can involve cost and use of medical resources on a majority of people who do not need treatment. Adverse effects of screening procedure (e.g. stress and anxiety, discomfort, radiation exposure, chemical exposure). Stress and anxiety caused by prolonging knowledge of an illness without any improvement in outcome. This problem is referred to as overdiagnosis (see also below). Stress and anxiety caused by a false positive screening result. Unnecessary investigation and treatment of false positive results (namely misdiagnosis with Type I error). A false sense of security caused by false negatives, which may delay final diagnosis (namely misdiagnosis with Type II error).
Screening for dementia in the English NHS is controversial because it could cause undue anxiety in patients and support services would be stretched. A GP reported "The main issue really seems to be centred around what the consequences of a such a diagnosis is and what is actually available to help patients."
Analysis