There are now several official NHS screening programmes testing for Breast, Bowel, and Cervix cancer and Aortic Aneurysms as well as high Blood Pressure and Cholesterol. There are also private companies offering to screen healthy people for early signs of various diseases using ultrasound and CT scans. The idea is that if one picks up a disease early it can be treated more effectively, so that lives can be saved.
Unfortunately, medical technology is far from perfect, and there are no screening tests which will without risk distinguish with complete certainty between people who are healthy and those who have a problem. This leads to problems for 2 groups of patients.
First of all most people with a positive screening test will not in fact have the disease concerned but will have to undergo a further test which may be painful and involve some risk - in order to find out that they dont have a problem. The anxiety involved can be severe,and it can take a long time to settle down.
Secondly some people who are diagnosed as having breast and prostate cancer in particular will end up having major surgery - when if their condition had been left alone the 'cancer' would have been non progressive and would have done them no harm. This problem is called 'overdiagnosis'. As a result of this problem - blood PSA screening for prostate cancer is not officially recommended by the NHS but is goes on nonetheless as a result of the publicity from various charities.
Because of these problems Medical opinion is divided over whether some of the official screening programmes such as for Breast and Bowel Cancer and Aortic Aneurysm are overall beneficial to patients. Information leaflets for these programmes have been severely criticized for failing to mention harms of screening. The NHS aortic aneurysm screening leaflet for the public makes no mention of harm at all.
Private screening companies of course are not concerned with benefit to patients. They do the tests and the problem of sorting out which of the patients actually have a problem then falls to the nhs. One of the most publicised tests is an ultrasound scan testing flow in the carotid artery in the neck. However there is no research into whether this test is a good predictor for patients who are at risk of strokes and heart attacks.
For further info. Read The patient paradox - by margaret mccartney - a scottish Gp.