The media continues to draw considerable attention to individual cases where screening has either been unavailable (e.g. young people with colorectal cancer) or unsuccessful (e.g. cases of colorectal cancer occurring where the screening test has been negative). In addition, there are constant pleas, requests and demands from a number of high-profile individuals and the many charities involved in screening to both broaden the spectrum of programmes available and expand the age range of those invited to participate in currently available programmes.
However, it is clear to many of us involved in provision of screening programmes that there are a number of widely-held misunderstandings about the principles and practices of screening, including the complex matter of balancing benefits and risks.
In the four countries of the UK, there are a wide variety of screening programmes from pregnancy screening through neonatal screening to screening of young people and adults: these are described in detail on the website of the UK National Screening Committee (http://www.screening.nhs.uk/programmes). Current screening programmes include those for colorectal, breast and cervical cancers. In addition, in England, there is an “informed choice programme”, Prostate Cancer Risk Management, which aims to ensure that men who are concerned about the risk of prostate cancer receive clear and balanced information about the advantages and disadvantages of the prostate specific antigen (PSA) test.
Many of these screening programmes rely on initial tests performed in clinical biochemistry laboratories and the other specialities of laboratory medicine. These include faecal tests for the presence of blood for colorectal cancer screening and liquid-based cytology for cervical cancer. Moreover, candidate screening tests, including CA-125 as a screening modality for ovarian cancer, are also performed in clinical biochemistry laboratories. Such laboratories also provide a range of tumour markers used in monitoring known cancers, including CEA, CA 15.3, CA 19.9, calcitonin, thyroglobulin and paraproteins. In consequence, professionals in laboratory medicine, particularly clinical biochemists, have a deep interest in ensuring the correct application of the tests done in their laboratories, including those used in asymptomatic population screening.
Many of these professionals have a deep interest in communicating facts about their generally rather out of the public eye activities to a broad audience and have delivered many initiatives. In a recent press release, the Association for Clinical Biochemistry and Laboratory Medicine drew attention to the latest offering from Making Sense about Science (http://www.senseaboutscience.org/), a new edition of the guide Making Sense of Screening: A guide to weighing up the benefits and harms of health screening programmes. The stated aim of the guide is to address the unrealistic expectations of what screening can deliver.
In this colourful and easy to read guide, replete with pictures of, and quotes from, acknowledged experts, screening is explained by scientists and clinicians including the following issues.
- Screening can identify some of the people who have or are at risk of developing a disease.
- Screening may cause harm, which needs to be balanced with the benefits.
- Some false positives and false negatives are the unavoidable cost of screening groups of people who have no symptoms of disease.
- Screening rarely benefits all sections of the population so it needs to be targeted at those most likely to benefit.
- Even when the benefits are clear at a population level, there is still potential harm for an individual.
This guide is freely available at http://www.senseaboutscience.org/resources.php/7/making-sense-of-screening. I think that the guide might be very useful to all those involved in the design and delivery of screening programmes, particularly when thinking about creating simple and understandable explanations for somewhat complex and difficult issues.
– Prof Callum Fraser