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What is screening?

Most people take part in screening in order to be reassured they are healthy, rather than with the expectation they are not. However, screening does not give you a diagnosis.

It does not tell you whether you do have the condition. Instead, screening sorts people into two groups: people who have an increased chance of having the condition (positive screening result) and people who do not have an increased chance of having the condition (negative screening result).

 

People with a positive screening result will be offered a diagnostic test, which will give more information about whether they do have the condition. People with a negative screening result will not be offered the diagnostic test. Depending on the type of screening, they may be invited to come back for screening at a later date (eg, for a repeat mammogram).

The benefits of screening

Screening programmes can detect some conditions and reduce the chance of developing or dying from some conditions. In some cases, such as breast screening, screening may detect cancer at an early stage. In other cases, such as newborn metabolic screening, screening may find conditions which can be treated before the baby develops a preventable illness or disability. For example:

  • breast screening reduces your chances of dying from breast cancer by about 30 percent if you are between 50 and 65, and by about 45 percent if you are between 65 and 69
  • cervical screening reduces your chances of developing cervical cancer by about 90 percent
  • newborn hearing screening picks up hearing loss in babies and young children at an early stage. This means help such as resources, parent support groups, hearing aids, cochlear implants and the introduction of sign language can be offered as soon as possible
  • screening pregnant women to see if they have HIV and offering treatment will reduce the number of babies born with HIV or getting HIV through breastfeeding. Screening could prevent several babies from getting HIV in New Zealand each year
  • newborn metabolic screening enables certain conditions that can be harmful to babies to be picked up and treated early, reducing illness and sometimes death.

Screening can provide some information about the chance of your baby having Down syndrome or other conditions, such as trisomy 18 (Edwards syndrome), trisomy 13 (Patau syndrome) and some other rare genetic disorders.

Does screening have risks?

All screening has the potential to cause harm. Screening tests carry a risk of false results.

A false-negative result is when a person who does have the condition is put into the group of people who have a lower chance of having the condition. False-negatives can provide false reassurance.

A false positive is when a person who does not have the condition is put into the group of people who have an increased chance of having the condition. False-positives can result in increased anxiety and referral for diagnostic tests.

The screening pathway

A screening test is carried out on people who do not have any symptoms but are perceived to be at risk of a particular disease. It predicts the likelihood of someone having or developing a particular disease.

Screening is far more than just having a mammogram, cervical smear test, hearing test, blood test, or other check.

Those who would benefit from screening are offered the opportunity to take part in a screening programme. This may be the person who will be screened, or in the case of a baby, their parent or caregiver.

The screening test is then carried out on the individual. This may mean going to a clinic or surgery, or in the case of babies, the test may be carried out in hospital or at home. After the screening takes place, some babies or adults may be offered further tests.

Organised and opportunistic screening

There are two types of screening - organised screening programmes and opportunistic screening programmes.

Organised screening programmes have to be of a high standard, and the screening services are checked and monitored by people from outside the programme. With organised screening programmes, everyone who takes part is offered the same services, information and support. Often, large numbers of people are invited to take part in organised screening programmes. The National Screening Unit oversees national organised screening programmes.

Opportunistic screening happens when someone asks their doctor or health professional for a check or test, or a check or test is offered by a doctor or health professional. Unlike an organised screening programme, opportunistic screening may not be checked or monitored.

How are decisions about screening programmes made?

The National Health Committee has developed a list of criteria against which decisions about new screening programmes can be assessed.

These criteria are:

  • the condition is suitable for screening
  • there is a suitable test
  • there is an effective and accessible treatment or intervention for the condition
  • there is high-quality evidence that a screening programme is effective in reducing death and illness
  • the potential benefit of the test should outweigh potential harm
  • the health sector should be capable of supporting diagnosis, follow-up and programme evaluation
  • there is consideration of social and ethical issues; there is consideration of cost-benefit issues.

 

Download: Screening to Improve Health in New Zealand: Criteria to assess screening program - PDF, 325 KB

For further information, read this document created by the National Health Committee (2003)