Screening, case finding and diagnosis

Screening, case finding and diagnosis

The tragic case of Sophie Jones has been reported in the press this week. This young woman died from cervical cancer at the age of 19. She had apparently requested a 'smear test', but was refused as she did not fit the criteria for the national screening programme. I do not know the precise way that request was framed, nor what relationship that request had with her abdominal symptoms, attributed to Crohn's disease. Nor are we told the timing of the request. Whether or not the smear test would have affected the outcome is impossible to know from the newspaper stories.
This case does illustrate the widespread confusion between screening, case finding and diagnostic testing. Screening tests are applied to entire sections of the population who are asymptomatic. Thus there are strict criteria applied to avoid causing more harm than benefit. There was also cost considerations. Screening programmes are not a replacement for diagnostic tests. If a woman has a problem with her breast between screening mammograms, she should go through the standard diagnostic workup. Similarly if a woman has symptoms or signs suggestive of cervical cancer. Statistics that apply to the asymptomatic population should not be applied to the symptomatic population. It is however worth pointing that deaths from cervical cancer across the entire population in this age group are very rare.
Case finding is the application of testing in a sample of the population selected on the basis of risk factors for a disease, for example a relevant family history.
Diagnostic testing is applied on the basis of relevant history, signs or symptoms.
It might be that diagnostic testing was indicated here at the time Sophie Jones asked for a smear. It might be that there was no reason to perform a smear test at that time. Either way, this case does not indicate a need to expand the screening programme - merely a need to consider diagnostic testing even when screening is not indicated. This is an unfortunate side-effect of screening, that it may lead to a rejection of appropriate testing - either through the false reassurance of a recent negative test, or the incorrect estimation of the likelihood of disease in someone ineligible for screening.