“The object of screening for disease is to discover those among the apparently well who are in fact suffering from disease. They can then be placed under treatment and, if the disease is communicable, steps can be taken to prevent them from being a danger to their neighbours.” These are the opening words in the preface to a book commissioned by the World Health Organization (WHO) in 1968, entitled Principles and Practice of Screening for Disease. The authors, Wilson and Jungner, continue: “In theory, therefore, screening is an admirable method of combating disease, since it should help detect the disease in its early stages and enable it to be treated adequately.”
My most vivid recollection of screening for disease occurred in 1986 when I took a job in the USA and my wife and I were required to have a chest X-ray, to screen for tuberculosis (TB), and provide a blood sample, to screen for the human immunodeficiency virus (HIV). If a positive diagnosis for either TB or HIV had been returned, then both of us, together with our children, would have been on the next plane back to South Africa. Fortunately we were healthy and did not pose a danger to our American neighbours, so the authorities allowed us to stay.
There are ten criteria for screening identified in the WHO guidelines: (1) the disease should be important; (2) there must be a latent or early symptomatic stage; (3) the natural history of the disease should be well understood; (4) there should be a suitable test or examination; (5) the test should be acceptable to the population; (6) screening of at-risk groups should be ongoing; (7) satisfactory treatment for the disease should exist; (8) facilities for diagnosis and treatment must be available; (9) there should be an agreed policy on whom to treat; and (10) totals costs should be economically balanced.
While there have been some great success stories — the blood test in newborns comes to mind — other screening programmes, including breast cancer, still remain controversial. The problem often relates to criterion number 4 where the test returns a false positive or false negative result. Since the harms caused by screening can be physical, psychological or financial they should not be overlooked by any company introducing a new test.
In 2014 our engineers at CapeRay are dedicated to the clinical evaluation and commercialization of a screening test for breast cancer that maximizes both sensitivity and specificity.