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Monday, 14 May 2012

Overscreening - a potential new public health problem

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Screening for disease prior to the development of overt manifestation of illness , also referred to as secondary prevention, has been a mainstay of public health practice.   Few would question the value of screening for cervical dysplasia/cancer, hypertension, newborn hypothyroidism and enzyme deficiencies,  or hypercholesterolemia.   Disease that once showing overt symptoms are often already past points of symptomatic intervention.  

Of course once diagnosed, there is an intervention that is required.  For cervical dysplasia that has been reduced to essentially a one-time cure.   The other illnesses noted above often require lifelong intervention and incur significant costs.  

Screening programs only work if they reach a high proportion of the population at risk for developing the disease – hence the cost can be significant.   Compound this where there are individuals or groups of individuals who stand to benefit from the screening program who are separate from where the cost benefits of early intervention are accrued and a fertile ground for abuse develops. That ground can extend to biased research and poorly founded recommendations.  

So in come the two major gender specific debates, screening for breast and prostate cancers. Both are still the leading cancer type for each of the sexes.   The outcomes of both illnesses are dreaded and frequently result in death, adding dramatization to the debate.   The cost of a mammogram is about $100, that of a prostate specific antigen (PSA) around is about half that.  Spread over millions of folks, that begins to look like a lot of money.   Add to the cost of screening is both have fairly high false positive rates that mean intervention in the absence of disease that would likely have progressed.  

So it is notable that within a short space of time there are finally some review articles and lay literature beginning to push back based on the negative consequences of overscreening.  Health Evidence has recently published two reviews, international mammography comparison  and meta-analysis of prostate screening raising concerns about current programs.  The former questioning the value of population based screening and not even delving into the debates of age-specific recommendations, the later further fuelling the evidence that PSA screening is not recommended.  

Link this with a newspaper article that actually looked at the value of whole body screening – the concept of doing CT or MRI scanning routinely of the whole body just to see if there are anomalies that should be acted upon.  A whole 86% of asymptomatic persons had an anomaly that if found in isolation would have resulted in further investigation.   The article further bemoans overdiagnosis of prostate and breast cancer  - it is a great read for lay persons and health professionals alike Oversceening Vancouver Sun.   

Notable in the 2012 Cancer statistics just released, there is multiple references to the value of screening for cervical, breast, prostate, and colorectal cancers without mention of the potential negative consequences. Screening and secondary prevention have a very clear role in public health,but also  in public health objectivity remains a core value, even in passionate debates over life and death.  Worse still is the confusion caused by supposed 'expert' advice that is conflicting.   Groups like the Canadian Task Force on Preventive Health Care were and are designed to wade through this myriad and develop defensable recommendations that all health care workers should follow http://www.canadiantaskforce.ca/

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