Screening, in the context of epidemiology and public health, refers to the process of trying to prevent disease and death through testing a targetted section of the population for early stages of a disease.
Ideal Screening Test
Doctors - perhaps especially specialist doctors - have an understandable urge to try to prevent the suffering caused by the problems that they deal with. Specialists may be inclined, as they see a lot of the condition they specialise in, to lose sight of the true incidence and prevalence of the condition, and of the value of proposed screening conditions. Private companies may prey upon people's anxieties to offer expensive and potentially harmful screening programmes. All screening programmes have costs as well as benefits. There has been little public awareness of the downsides of screening (with a few notable exceptions). Policy makers therefore need to have clear criteria for deciding whether a screening programme is worthwhile.
- important condition
- untreated natural history understood
- recognisable latent or early stage
- acceptable treatment
- diagnostic and treatment facilities available
- early treatment should lead to better outcomes than late treatment
- test should be sensitive, specific, reproducible, validated and safe
- distribution and cut-off points for the test should be known
- acceptable to patients
See Interpreting test results for more information.
- target population agreed
- continuous screening (interval agreed)
- adequate resources
- ideally supporting randomised-controlled trials in favour of screening
Benefits and disadvantages of screening
(Table adapted from J Chamberlain, 1988, which was concerned with breast cancer.)
Examples of potential or actual harmful effects of screening
(This list is currently very incomplete.)
Reporting of screening in the media tends to be biased towards reporting the potential benefits - and not the potential harms - of screening. Ganfyd may be able, here, to collate some studies which highlight potential harms from screening.
- Negative effects on body image and capacity following bone density screening (small qualitative study).
See also Mcartney's book.
The whole basis of public health interventions is different to that of the traditional medical consultation. When proactively recommending a medical intervention to somebody who has not asked for it, the strength of evidence of benefit, and of lack of harm, must be much stronger.
When a patient goes to a doctor (doctor is used here as a metaphor for the wider health system) asking for help, the doctor's ethical duties are reasonably clear. They should respond to the patient's request as best they can, in the patient's best interests, endeavouring to do no harm, and so forth.
When approaching an individual who has not asked for help the onus on the doctor to know that what they propose is likely to benefit that individual and the society, and not to do harm, is much greater. The complexity of the information makes it harder to provide patients with truly "informed choice" as to whether to consent to screening, and risks inadvertent overmedicalisation and overtreatment. Well-intentioned advice which turns out to be wrong can do great harm: the advice from the US' surgeon general to lie babies on their fronts so that they don't aspirate if they vomit caused many infant deaths, for example. Advice based on poor-quality evidence that has to be changed when newer or better quality evidence arises erodes people's confidence in public health advice. A screening programme which provides little benefit diverts resources from activities that could provide greater benefit, breaching the ethical principle of "justice".
Rarely, tests will raise ethical issues relating to people other than the individual screened.
- If an antenatal screen for Down's syndrome or spina bifida will result in the offer of a termination of pregnancy, is it appropriate to do the test if the parents have stated that they will not consider termination whatever the result?
- If someone is diagnosed as having Huntingdon's Chorea, half their children are likely to inherit. Some offspring may prefer not to know what lies ahead. What if a grandchild wishes to know even though the parent does not? If the grandchild is positive then the parent must have passed it on. How does one manage this situation?
No answers are provided as patients and doctors are individuals who will have their own viewpoints. Each must think the position through individually and act upon it. Sometimes a doctor may feel that he or she must withdraw from the case. Patients do not have that option. Sudden decisions are unwise and an opinion from a department of Medical Ethics or a Defence organisation may be required. Optimally this should occur during the planning of the program rather than in a quick scramble half way through. Life is not like that.
Jargon relating to screening
- Interval cancer
- A clinically overt cancer which develops in the interval between scheduled screening episodes. Interval cancers can be used to monitor the appropriateness of the interval between screenings; but also (and more or equally importantly) to trigger checks on the quality of the previous screening - was the smear really NAD?
- Length-time bias
- Makes it more likely that you will detect slow-growing cancers.
- Lead-time bias
- Makes survival “improve” artefactually, by simply diagnosing the condition earlier. Well defined in “Clinical Epidemiology”.
Examples of screening programmes
These may include:
- Newborn blood spot Guthrie tests
- Developmental dysplasia of the hip
- Child checks
- Non-Cancer Screening Programmes:
- NHS Abdominal Aortic Aneurysm Screening Programme
- NHS Diabetic Eye Screening Programme
- NHS Fetal Anomaly Screening Programme
- NHS Infectious Diseases in Pregnancy Screening Programme
- NHS Newborn and Infant Physical Examination Programme
- NHS Newborn Blood Spot Screening Programme (using the Guthrie card) for phenylketonuria (PKU), congenital hypothyroidism (CHT), sickle cell disease (SCD), cystic fibrosis (CF) and medium-chain acyl-CoA dehydrogenase deficiency (MCADD).
- NHS Newborn Hearing Screening Programme
- NHS Sickle Cell and Thalassaemia Screening Programme
- Cancer Screening Programmes:
There have also been a number of programmes that are screening programmes in all but name. The evidence base for these has been questioned; and some have even suggested that there may be ulterior political motives for their introduction. They include:
- NHS Health Checks have been promoted since ??2008. Introduced under a labour government led by Gordon Brown, they have been continued - albeit, according to some, for different political reasons - under Cameron's coalition government. According to the healthcheck web site, the checks are about "helping you to prevent heart disease, stroke, diabetes, kidney disease and dementia". Critics claim that the checks will lead to further overmedicalisation of the worried well, not reach those who really need them, and not be cost effective. Documentation at the healthcheck web site claims otherwise; and the site also claims that the programme's value will be rigorously evaluated.
- Dementia screening has been discussed in 2013. It is not entirely clear whether this is separate from NHS Health Checks. This has been controversial, partly because it is not clear that there is a robust screening test, or an effective, acceptable, and cost-effective treatment to offer.
Private screening companies
A number of companies have realised that there is a market for private screening, and have started marketing themselves to people who can afford to pay enough for them to make a profit.
Some of the screening on offer from such companies may not meet the criteria above, and may even do more harm than good.
Robust advice on whether such screening may be of value can be found at the PrivateHealthScreening web site.
- See NHS Cancer Screening Programmes website:
- Breast cancer screening
- Cervical cancer screening
- Colorectal cancer screening
- (Ovarian cancer screening is NOT recommended.)
Areas of uncertainty
- Streptococcus agalactiae in pregnancy.
- Barrett's oesophagus - to prevent oesophageal cancer
- GFR to screen for chronic renal disease.
- Testing a Screening Test
- Thinking of having a private screening test? leaflet from the UK National Screening Committee.
- UK National Screening Portal (formerly the UK National Screening Committee, at http://www.nsc.nhs.uk/).
- NHS Evidence - screening. The National electronic library for health used to have a specific screening portal, which replaced its "screening branch library" - but it no longer seems to exist.
- Making Sense of Testing: why scans and health tests for well people aren’t always a good idea leaflet and web page from sense about science.
- PrivateHealthScreening web site, which was established by "a group of doctors who are concerned about the safety and the ethics of private screening tests. We are worried that the companies who charge you for these tests are not giving consumers full and fair information about them."
- Pod Delusion episode 129 - with a piece on screening for a educated lay audience by Margaret McCartney
- ↑ Gray JA, Patnick J, Blanks RG. Maximising benefit and minimising harm of screening. BMJ (Clinical research ed.). 2008 Mar 1; 336(7642):480-3.(Link to article – subscription may be required.)
- ↑ Ablin RJ. The great prostate mistake 2010; Updated 9 March; Accessed: 2010 (22 March): Opinion
- ↑ Wilson JMG and Junger G. Principles and Practice of Screening for Disease. WHO Public Health Papers No. 34, 1968. (Direct link - large pdf ~7Mb)
- ↑ UK National Screening Committee. Criteria for appraising the viability, effectiveness and appropriateness of a screening programme. 2003. Last accessed January 15, 2007.
- ↑ Day NE, Chamberlain J. Screening for breast cancer: workshop report. European journal of cancer &amp; clinical oncology. 1988;24:55-9.
- ↑ Bedeman JW, Meisel SF, Pashayan N. Annals Graphic Medicine: Living on Benefits: How Cancer Screening Is Portrayed in the U.K. National Press. Annals of internal medicine. 2016 May 3; 164(9):W13-4.(Link to article – subscription may be required.)
- ↑ Reventlow SD, Hvas L, Malterud K. Making the invisible body visible. Bone scans, osteoporosis and women's bodily experiences. Social science & medicine (1982). 2006 Jun; 62(11):2720-31.(Link to article – subscription may be required.)
- ↑ McCartney M. The Patient Paradox: Why Sexed Up Medicine is Bad for Your Health: Pinter & Martin Ltd, 2012
- ↑ Johansson M, Jørgensen KJ, Getz L, Moynihan R. “Informed choice” in a time of too much medicine—no panacea for ethical difficulties. BMJ 2016;353.
- ↑ http://www.newbornscreening-bloodspot.org.uk/
- ↑ NHS England. Immunisation & Screening National Delivery Framework & Local Operating Model 2013 (23 May)
- ↑ NHS Cancer Screening Programmes website
- ↑ Hallan SI, Dahl K, Oien CM, Grootendorst DC, Aasberg A, Holmen J, Dekker FW. Screening strategies for chronic kidney disease in the general population: follow-up of cross sectional health survey. BMJ. 2006 Nov 18;333(7577):1047. (Direct link - subscription may be required)
- ↑ Clase CM. Glomerular filtration rate: Screening cannot be recommended on the basis of current knowledge.BMJ. 2006 Nov 18;333(7577):1030-1031. (Direct link - subscription may be required)