Screen test - what is screening and why can't we screen for everything?

Screen time: what is a screening test and why do we have them?

Most of us will be familiar with a few of Australia’s screening programs, like the bowel cancer screening program or mammograms for breast cancer screening, but what does screening actually mean, and why don’t we just screen everybody for everything?

What is screening?

Screening tests could be loosely defined as proactive rather than reactive. A screening test is performed as a preventative measure – to detect a potential health problem or disease in someone that doesn’t yet have signs or symptoms.

The purpose of screening is early detection; helping to reduce the risk of disease, or to detect a condition early enough to treat it most effectively.

For example, a person having an HbA1c test for diabetes as part of a screening program could be found to have prediabetes. Diet and lifestyle changes combined with regular monitoring tests can allow someone with prediabetes to avoid developing type 2 diabetes.

Screening tests are not usually diagnostic, but are used to identify those who should have additional testing to determine the presence or absence of disease, or people who may benefit from early intervention measures.

Who gets screening?

Screening programs are tailored toward those who the disease is most likely to affect and where the most benefit can be gained. For example, when looking at cervical cancer screening, several factors are taken into consideration in choosing in who to screen including:

  • Sex. Men cannot get cervical cancer (they do not have a cervix!) so only women are tested.
  • Age. Women below the age of 25 are less likely to be affected by cervical cancer, so the majority of women will be offered the test from the age of 25 (This may differ for some women depending on medical and family history).
  • Vaccination. The screening test is not diagnostic of cancer, it tests a woman for Human Papilloma Virus (HPV) – which is present in the majority of cervical cancer cases. The HPV vaccine was introduced in Australia in 2007 meaning many young Australians are vaccinated, reducing the prevalence and spread of HPV. However, not all women are vaccinated and there is still a risk of cervical cancer even in vaccinated women meaning it’s important for women to take part in screening.

How is it decided what diseases will be screened for?

Several factors need to be assessed when making a decision about screening for a disease, these include but are not limited to:

1. Is there a screening test available?

For some conditions there may not be a test available that is suitable for screening – one that can be made widely available to the eligible population and fulfils the purpose of early detection or identifying those at high risk. For example, for the bowel cancer screening test, the faecal sample is taken by the patient at home and mailed to the lab for free making it highly accessible. The test is offered to all those over 50 and is not dependent on symptoms – as bowel cancer often has no symptoms at its earliest and most treatable stage.

2. How common is the condition?

Screening a large number of people for a condition that is rare in the Australian population is of limited benefit. Therefore screening for a condition is often confined to a specific section of the population based on certain risk factors – for example age.

That being said, newborn screening is offered for each newborn baby, even though some conditions screened for are quite rare. This is because early detection and treatment can save lives and allow children to lead a full life into adulthood.

3. How serious is the condition?

Screening tests are usually focused on conditions that may be fatal or have very serious health impacts such as severe physical and mental disability if left untreated. However, screening can be broader than this. For example, testing for infectious diseases that could be passed on to others (for example tuberculosis screening for immigrants), or genetic screening for prospective parents to know if they are carrying a gene associated with a serious disease that may be passed on to a child.

4. Can the condition be treated? (And does early detection make any difference?)

Some serious conditions have no cure and limited treatment options, these are unlikely to be candidates for a screening program as there is little benefit to be gained from early diagnosis. All conditions included in newborn screening programs will benefit from early detection, with treatment most effective at the earliest stage, hence the decision to screen very soon after birth.

5. Cost vs benefit.

The cost of providing the screening program is weighed up against the benefits of catching the disease early or preventing it developing. The benefit to the patient is clear but economic benefits are also looked at. This includes:

  • the cost of treating a disease e.g. cancer at a later stage. This is typically more expensive to the health system
  • the cost to the economy of a person’s illness or disability resulting from untreated illness.

These costs can range from the economic impact of lost productivity from time off work, lost productivity of family members acting as carers, as well as the cost of disability support services and economic loss where someone is unable to participate in work and the community more broadly.

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