Last partial update: July 2016 - Please read disclaimer before proceeding

 

Screening - Helping to diagnosing disease before its symptoms have occurred

Screening for a disease involves asking a question or performing an investigation to help indicate which patients may have that particular serious disease. Most people are aware of the commonly recommended cancer screening tests but there are many other types of disease that can be screened for. Examples include cardiovascular disease (heart attacks), diabetes, Down syndrome and kidney disease.

Most screening tests do not provide a diagnosis. Rather they assist in identifying people at increased risk of the condition being screened for. Further investigations are usually necessary to make a definite diagnosis. (There are exceptions to this general rule, an example being the use of blood glucose testing to screen patients for diabetes.)

It is very important to understand that screening is done on people who DO NOT have / have not had symptoms of the disease. Screening tests are not the appropriate method for investigating people with a history of disease symptoms. People with a history of symptoms require different investigation and investigations and need to have this done by their doctor as soon as possible.

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Screening needs to be proven to be beneficial

Screening is done on individuals who are usually fairly healthy and who are not at significantly increased risk from the disease being screened for. For this reason it is fundamentally important that, before any screening program is introduced, well-conducted studies are done to prove that the program improves significantly the overall life expectancy / life quality of the tested population.

It is important to recognize that the benefit provided by screening is assessed according to its affect on the overall group being tested and that there is NO guarantee that any particular screened individual will benefit. In fact, in most screening programs, the vast majority of participants will gain no benefit at all and will in fact be slightly worse off. (They all have to endure the inconvenience, possible discomfort and worry involved in testing.) However, the few that do benefit often do so enormously. Thus, what the above-mentioned studies need to establish (without doubt) is that the large benefit gained by a few (through early diagnosis that leads to improved treatment and a better patient outcome) significantly outweighs the usually small ‘price’ paid many. (As we shall see later, a very small number of people will pay a larger price.)

Numerous screening tests are recommended to patients by health practitioners without proof of benefit. (Government health authorities do not recommend such tests.) At the end of this section there is a list of screening tests available through doctors for which convincing evidence of benefit is lacking. Other health practitioners also sometimes recommend screening for patients without evidence of benefit. (Breast cancer screening using thermography (thermal imaging) is an example.) Please remember that the existence of a test does not imply its use is justified!!!

Deciding whether a particular screening program will be of benefit to you

While the early diagnosis provided by screening tests can reduce illness and even prevent premature death, it is very important to emphasise that all screening involves doing medical procedures on WELL people that are intrusive, cost money and involve side effects. Therefore, as mentioned above, it is critical that a substantial overall benefit exists for those being screened before a screening program is implemented. The following quote emphasizes what this implies for doctors recommending a screening procedure. 

“For decades, Australia has accepted the World Health Organization guidelines for evaluating the worth of screening. These guidelines, recently updated, state “. . . in screening there is an ethical responsibility to conduct programs that will be of overall benefit to those who are screened and will minimize harm and anxiety that will arise. It is not simply the offering of medical tests for people to accept or reject as they wish. This responsibility implies that if evidence is not available from valid studies on the effectiveness of screening, screening should not be offered.”

Strong K, Wald N, Miller A, Alwan A, on behalf of the WHO Consultation Group. Current concepts in screening for noncommunicable disease: World Health Organization Consultation Group report on methodology of noncommunicable disease screening. Journal of Medical Screening 2005; 12; pp12 - 19

For screening programs to be of benefit to the community, then the majority of the community being offered the test needs to participate. However, it is important to realize that with most screening programs, only a few participants receive any overall benefit and most will not benefit at all from screening. However, the benefit gained is often a large one, such as cure from cancer.  It is a bit like buying a lottery ticket. Everyone participating contributes a little bit so that a very small number of people can win a lot. (See boxed section below.)

Deciding on whether an individual will benefit from being screened for a particular cancer is a matter of balancing the following factors.

  1. The risk the person has of contracting the disease. An important factor here is age. Almost all cancers increase in incidence with age and thus screening provides a relatively greater benefit as a person gets older. Eventually though this age benefit is balanced by the fact that people are increasingly likely to die from another condition as they get older. Thus, screening is generally not recommended in people over the age of 70 years as the possible benefit is not worth the ‘costs’ involved. (There are a couple of exceptions to this rule.)
  2. The likelihood that the disease will cause harm. (Some diseases will never develop into a serious condition, especially in the elderly.)
  3. The accuracy of the screening test. It is important to understand that no screening test is 100% accurate. There will always be:
      • False negative tests, where the test misses a condition that is present. For example, stress tests done on people without heart disease symptoms misses about 30% of cases of heart disease. Mammography misses about 30% of cancers.
      • False positive tests, where the screening test indicates an increased risk of disease being present but none is found to exist with further testing. This means that unnecessary investigations are conducted and also means the person worries unnecessarily that they have a condition.
  4. The risks involved in having the screening test. More invasive screening techniques are not without risk (or expense) and should therefore be restricted to those who would definitely benefit from the test. Remember that people can suffer a complication from the screening test even when they have no disease present.
  5. The risks involved in subsequent investigations and therapies required for diagnosis and successful treatment.
  6. The benefit early detection provides. Screening to find a disease early is of little use if its early detection does not improve the treatment outcome. This will depend on;
      • whether in most cases the screening test finds the disease early enough for treatment to provide an improved outcome. (Chest X-rays do not achieve this for lung cancer.)
      • whether the available treatment for the disease improves the person’s life expectancy. In some people, especially the very elderly and those with other serious illnesses, this will depend in part on pre-existing disease and overall life expectancy.
      • Whether the available treatments for the disease offer a better outcome than adopting a wait-and-see approach. If this is not the case, then screening should not be advised. (This is the one of the controversial issues surrounding the present debate about routine screening for prostate cancer.)

Many of the above considerations have already been taken into account as part of the Government’s decision making process regarding whether or not to recommend a screening program. A few however cannot be and individuals need to look at these with their doctor before deciding on whether to participate in a screening program. The most important ones are:

So, for example, it may well be that a person who suffers significantly from anxiety / depression and who smokes may decide that the possible benefits of a screening program do not outweigh the inconvenience / risks involved and thus may choose not to participate. It is a free country. (Of course the best health option would be to have the screening test AND address the other health problems.)

Screening decision aids

From the above it can be seen that deciding whether to have a screening test or not can be reasonably complicated. Luckily, some ‘decision aids’ have been designed to help people make this choice and many more are being presently designed. (See ‘Further information’ at the end of this section. The Ottawa Health Research Institute and Sydney Health Decision Group web sites are a good place to start.)

Government recommended screening

Government health authorities in Australia are very aware of all the above issues. In addition, they have to consider the high financial cost of running screening programs. (While the financial cost of screening varies depending on whether or not each screening test is associated with a GP visit, a very rough guide to the overall cost of cancer screening is about $25,000 per year of life saved.) Governments have many worthy alternative uses for funds spent on health and thus are only likely to recommend screening where there is a clear overall benefit to the population who participate and their approval for a screening program should help people make this decision (and visa versa).

Even so, the benefit gained is an overall community one and there is no guarantee that any particular individual will benefit. So it is a personal choice.

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Abnormal screening tests are common

Screening programs commonly involve having tests at regular intervals over an extended period of time and each time there will be, as well as true positive results, a number of false positive results; that is, tests that indicate a problem might exist in a person where no problem actually exists. Most women (and a considerable number of men) who choose to participate in recommended cancer screening will have at least one abnormal screening test result at some time in their lives and this is also the case in screening for diseases such as heart disease.
In women who choose to participate fully in the recommended screening programs for breast, cervical and colon cancer;

Obviously most of these abnormalities will be false positives but they will all cause stress and worry while they are being investigated. (And some people will continue to worry after being cleared of disease.)

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Screening tests recommended for Australians

 

All the below recommendations are for people who are NOT at increased risk of disease. Those at increased risk may need earlier screening and additional/ different types of screening tests.

 

All Australian adults (at normal risk of the disease*)

 

 

Disease

Screening test

Starting age*

Cardio-vascular disease

(Heart attacks)

Australian cardiovascular risk charts

http://www.heartfoundation.org.au/SiteCollectionDocuments/A_AR_RiskCharts_FINAL%20FOR%20WEB.pdf

(See section  ‘Assessing your heart attack risk.’)

This involves having a blood test for cholesterol, a blood pressure measurement and in many people a test for diabetes.

 

45 years

Diabetes

 

AUSDRISK Australian Type 2 Diabetes Risk Assessment Tool. 

http://www.bakeridi.edu.au/aus_diabetes_risk/

(See section on diabetes.)

35 years

Fasting blood glucose level

 

55 years

Kidney disease

Check blood pressure and urine test

50 years if not done before.

Bowel (colon) cancer

Faecal Occult Blood testing (Checks to see whether there is blood in the bowel motion, an occurrence that is more common in bowel cancer.)(Second yearly)

(See section on bowel cancer.)

50 years

Osteoporosis

The international Osteoporosis Foundation has a ‘One minute’ Risk factor identification test (online); http://www.iofbonehealth.org/patients-public/risk-test.html

Risk factor assessment is discussed in section ‘ Fracture Prevention in adults – Osteoporosis and fall prevention’

Women at menopause.

 

Fall prevention

Screening with GP to identify risk factors

65 years

Blood pressure weight / physical activity

GP Check Up (Second yearly)

Blood pressure check / Weight measurement / waist measurement

18 years

Chronic glaucoma

(a cause of loss of vision)

Measurement of eye pressure and visual fields (Done by an optician or an eye specialist.)

45 years

Additional tests for all Australian women (at normal risk of the disease*)

 

 

Disease

Screening test

Starting age*

Breast cancer

Mammography (Second yearly)

50 years

Cervical cancer

Pap smear (Second yearly)

Within two years of first sexual intercourse

Vaccination against Human Papilloma Virus

12 to 14 yrs

Before and during pregnancy

 

There are many health issues for both mother and baby that need to be addressed before and during pregnancy. These include:

  • Genetic abnormalities such as Down syndrome, cystic fibrosis, hereditary haemo-chromatosis, Fragile X Syndrome, Thalassaemias etc
  • Infectious diseases
  • Dietary considerations, such as dietary folate and iodine supplementation.
  • Alcohol, tobacco and other drug use

All pregnancy related health issues are best considered prior to pregnancy occurring because:

  • For some issues, gaining maximum benefit requires interventions / therapies / decisions to be made prior to pregnancy occurring
  • Some issues are complex and need time for parents to consider properly. (This especially applies to issues requiring genetic counselling.)

All the above issues are covered in the section on ‘Preparation for Pregnancy.

 

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Screening tests where benefit has NOT been proven

The following tests are NOT recommended for use as screening tests in Australians who are not at increased risk of the disease being screened for. (The tests may well be used in people who have symptoms for the disease or who are, for some reason, at increased risk of having the disease.)
This list is not complete and only includes tests commonly used by doctors.  (The list is adapted from information in ‘Guidelines for preventative activities in General Practice’, published in April 2009 by the Royal Australian College of General Practitioners.)

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Government recommendations for cancer screening

U.S. Preventive Services Task Force (USPSTF) cancer screening ratings

In the USA, the U.S. Preventive Services Task Force (USPSTF) rates its recommendations regarding screening as follows.

A rating: The USPSTF strongly recommends that clinicians provide [the service] to eligible patients. The USPSTF found good evidence that [the service] improves important health outcomes and concludes that benefits substantially outweigh harms.
B rating: The USPSTF recommends that clinicians provide [this service] to eligible patients. The USPSTF found at least fair evidence that [the service] improves important health outcomes and concludes that benefits outweigh harms.
D rating: The USPSTF recommends against the service. There is moderate or high certainty that the service has no net benefit or that the harms outweigh the benefits.
I rating: The USPSTF concludes that the evidence is insufficient to recommend for or against routinely providing [the service]. Evidence that the [service] is effective is lacking, of poor quality, or conflicting and the balance of benefits and harms cannot be determined.

Ratings for common cancers (and the year they were made) are as follows:

  • Bowel cancer screening using FOBT (faecal occult blood testing) for adults under 75 yrs old – ‘A’ rating (2008) Click here
  • Cervical cancer screening using Pap smears -  ‘A’ rating (2003) Click here
  • Breast cancer screening - ‘B’ rating (2009) Click here
  • Prostate cancer screening using the PSA test -  ‘D’ rating (2012) (Previously it had an ‘I’ rating.) Click here

Source: US Preventive Services Taskforce:  www.ahrq.gov/clinic/cps3dix.htm#cancer

 

 

Australian Government recommends for cancer screening for normal risk people

(People with an elevated risk of a particular cancer will need to discuss earlier / additional screening with their doctor.)

Cancer type

Screening procedure

Frequency

Females

   Cervical cancer

Pap smear

Every 2 years from age 20 or two years after first sexual intercourse. Usually ceases at age 70 where no cervical abnormalities have occurred.

   Breast cancer

Mammogram

Every second year from age 50 to age 70

   Bowel cancer

FOBT (Testing for blood in bowel motions)

Every two years from age 50 to age 70

Males

   Bowel cancer

Testing for blood in bowel motions

Every two years from age 50 to age 70

   Prostate cancer

There is insufficient evidence for government health authorities to make a decision regarding recommending routine screening for prostate cancer.

 

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Participating in a screening program is a bit like buying a lottery ticket; and a bit not!!

In a way screening is a bit like buying a lottery ticket. Lots of people participate for a relatively small cost so that a randomly selected few gain ‘the big prize’. However there are several major differences in the screening lottery and knowledge regarding these is important when making a decision about participating in screening.

Firstly, a favorable difference; overall, the odds are better. In normal lotteries, the lottery owner (the Government) keeps some of the contributions; so as a group the participants are worse off. Of course there are a few big winners, but most gain nothing. In the screening lottery, most participants still gain nothing for their contribution; but as a group the contributors are better off. This is because, before initiating a screening program, the Government health authorities have examined carefully all the evidence and made sure that the proposed program does offer those who participate a considerable overall benefit. (Why would they do it otherwise? After all, the program does cost the Government money to run and there is plenty of worthy competition for the health dollars spent on screening programs.)

Another difference is that in the ‘screening lottery’, those who benefit do not benefit equally. For most, the advantage in winning the screening lottery will be very considerable and they would be well advised to participate in screening. For others the following facts make the decision less clear. (And this means that everyone needs to think about screening before they accept the Government’s invitation to participate.)

Fact 1: In a normal lottery, the winner gets the same prize no matter who it is. In a screening lottery this is not the case. It varies depending on the winner’s health and age.
Looking at mammography screening for breast cancer can give us some insight into this. Here, the winner of the screening ‘first prize’ is the woman who has a potentially lethal cancer cured. For most women, this is a really major prize!!
However, this does depend on the health of the winner. A 60 year old winner who smokes will on average die 15 years before a winner who doesn’t. If we assume that a healthy non-smoking woman aged 60 would live till 86, then the non-smoker gains 26 years of life while the smoker gains only 11 years. A woman who has significant heart failure following a heart attack is likely to die before any breast cancer could kill her and unlikely to gain no benefit at all! So, before participating in screening, women should discuss issues that might reduce their potential benefit to ensure they are likely to gain benefit.

Fact 2:  There is a definite age group that benefits most from screening. This depends on the interplay of two factors:

Thus, generally speaking, people need to be aware that having screening done outside the recommended age groups means that, as a group, they are likely to gain a significantly reduced benefit.  (Younger ‘winners’ gain a bigger prize but there are very few of them; while the more common older winners do often not gain much of a prize at all.)

Fact 3: In a normal lottery, all the tickets cost the same amount. In a screening lottery, not everyone pays the same amount to participate. Taking the example of mammography for breast cancer screening again, all women who participate pay a minimum participation fee of the inconvenience, discomfort and ‘worry about results’ associated with having 10 mammograms between the age of 50 and 70 years. However, a considerable number of these women also have to make subsequent ‘additional payments’. Lets look at the payments made by 100 women between the age of 50 and 70 who choose to have mammography screening.

This benefit may sound small but it represents a reduction in death from breast cancer IN THIS AGE GROUP (not overall) of about 35% and over a large population represents many 1000s of relatively young lives saved each year. That is why both Government health authorities and doctors recommend mammography screening.

These ‘extra payments’ are incorporated into the Government’s decision regarding the overall benefit to the people who participate in the program. However, they mean that not everyone contributes equally to the ‘cost of the program’. In most cases it is not possible to know beforehand if a particular person is likely to be one of these ‘extra contributors’. However, in a few cases it is. One such case is people who suffer significantly from anxiety. In screening programs where finding some sort of abnormality is not uncommon, people who suffer anxiety are likely to suffer unduly and even when if they are subsequently given the ‘all clear’, they may not fully believe the result. Their suffering is very real and can be very debilitating.

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Different levels of screening

In some diseases, there are different ‘levels’ of screening available for people with different risk levels for the disease. For example, testing the faeces for blood is an easy non-invasive screening test for bowel cancer that is suitable for everyone over the age of 50. Colonoscopy is a more invasive, risky, and expensive procedure that is usually only recommended as a screening test for people who have a higher risk of bowel cancer.

 

Further information

NSW Cancer Council (For information about any cancer topic)
http://www.cancercouncil.com.au/sem-ways-to-donate/?gclid=CPP12-e1_80CFQFvvAodW7gD6Q

Harvard University cancer risk assessment
http://www.diseaseriskindex.harvard.edu/update/
An interesting web site that allows people, by answering a variety of questionnaires, to calculate their personal risk of developing different types of cancer, including breast colorectal and prostate cancers. It also helps identify factors that can modify / reduce a person’s overall chance of contracting the particular cancer being looking at.

US Preventive Services Taskforce (ratings on the benefits and harms of screening for common cancers)
http://www.ahrq.gov/clinic/cps3dix.htm#cancer

Sydney Health Decision Group at the School of Public Health, University of Sydney
http://sydney.edu.au/medicine/public-health/shdg/

Sydney University Bowel cancer screening aids
http://sydney.edu.au/medicine/public-health/step/publications/decisionaids.php

Australian Screening Mammography Decision Aid Trial
http://www.mammogram.med.usyd.edu.au

Informed health online (Cochrane Consumer Collaboration)
http://consumers.cochrane.org

The Cancer Council Australia
http://www.cancer.org.au/

UK National Screening Committee
https://www.gov.uk/guidance/nhs-population-screening-explained

US National Cancer Institute
http://www.nci.nih.gov/

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