Health Screening as a Strategy for Preventive Medicine
Lifted from Philippine Guidelines on Periodic Health Examination – 2004
In the last half century, health care has seen a major shift in philosophy from curative medicine to preventive medicine. Medical education has evolved, societies on preventive medicine have been formed, national and international agencies have been set-up, and health budgets have been reallocated – all in support of this important shift in medical thinking. In the process, the concept of health care has escaped the confines of clinics and hospitals, expanding into the public arena, to include homes, schools, and the workplace.
Thus far, four major strategies have been used in the rapidly growing field of preventive medicine. These include 1) health screening (doing tests for early detection of disease or risk factors for disease), 2) lifestyle change (avoidance of unhealthy habits). 3) risk factor control (treatment of factors that predispose to disease), and 4) vaccination programs (immunization against infectious diseases). Health screening is often referred to as the cornerstone of disease prevention, and although it often overlaps with the latter three strategies, it is the main focus of this book.
The World Health Organization (WHO) in 1994 defines screening as the use of presumptive methods to detect unrecognized health risks or asymptomatic disease in apparently healthy individuals in order to permit prevention and timely intervention. Screening is performed to categorize members of the general public into those with higher or lower probability of disease, with the former group being urged to seek further medical attention for definitive diagnosis and treatment.
Pitfalls of Screening and Other Preventive Medicine Strategies
Just like in curative medicine, the biggest pitfall in disease prevention is that things that ought to work do not always do so. For example, some lifestyle changes, such as salt restriction, have failed to lead to appreciable changes in the incidence of stroke and coronary disease in the general population. Most dietary maneuvers, like high fiber diet, have not been proven effective in cancer prevention. Risk factor control has failed as well, and in some instances, has even led to an increase in deaths. The cholesterol lowering drug clofibrate, for example, was removed from the market because a trial by WHO showed more deaths among patients who received the treatment.
Even the strategy of screening (executive check-ups) has had its failures. Many tests, such as the electrocardiogram, have been found to be inaccurate for detection of early coronary disease. As a result, many asymptomatic patients were wrongly labeled as being “ill.” Instead of improving the quality of life of people, this phenomenon of “false labelling” has been found to wreak havoc on the social, psychological, physical and financial stability of unfortunate individuals. Otherwise productive people have been denied insurance or employment, or have resigned from work because of depression. Many times, the side effects of screening have been far worse than the effects of the diseases which we were trying to prevent in the first place.
Furthermore, although treating early disease may be cheaper and easier, the saving are often offset by the costs of having to do the screening tests on large numbers of apparently healthy individuals. For example, curative surgery for a case of coronary artery disease (CAD) may cost half a million pesos in the Philippines. In contrast, primary prevention of a single death from cardiovascular disease may entail treating at least 143 patients for high cholesterol with a statin for 5 years. Depending on the statin used, this may cost as much as 20 million pesos. Indeed, sometimes, pounds of prevention translates to just an ounce of cure.
Criteria for Screening
Because health screening carries the potential for harm, and because it can lead to huge increments in unnecessary public expenditures, criteria need to be set on when screening for early disease should be done. Many such criteria have been developed, but most authors refer to the criteria discussed below.
- Treatment for the asymptomatic condition must have been evaluated using well-designed randomized controlled trials that observed effects on clinical outcomes.
It is easy to comprehend that if we spend millions of pesos to detect a disease for which there is no effective treatment, then the act of screening would have been rendered futile. What is difficult to decide is when to consider a treatment effective. A treatment is usually considered effective if it has undergone thorough evaluation in a randomized controlled trial. In such a trial, patients with the disease in question are randomly assigned to receive either the new treatment or a comparison treatment (which can either be placebo or an old standard therapy). If such a trial shows that patients do better on the new treatment, then it is generally considered effective. Such studies could support a recommendation to screen for disease. However, the study should show patient are doing better not just biochemically (e.g. cholesterol is lower), physiologically, (e.g. blood pressure is better), or anatomically (e.g. coronaries are more widely open). Doing better should mean patients actually feel better, or live longer, free from disease.
- The burden of illness from the asymptomatic condition must have been measured accurately in locally-conducted community-based studies.
Burden of illness refers to either the prevalence of disease or its impact on people’s lives. If a disease is very rare, or if it is inconsequential, screening for it may not be a worthwhile exercise. Studies on burden of illness should be done in the community-at-large because studies based in hospitals or clinics tend to include patients with severe illness and tend to exaggerate the true prevalence of the condition.
- Accuracy of the screening test for the asymptomatic condition must have been evaluated in validation studies done in the community.
All tests have types of error rates that should be minimized before they can be accepted as screening tests. A false positive error refers to a positive test result in a patient who does not really have disease, while a false negative error refers to a negative test result in a patient who actually has the disease. The hazards of false negative tests are easy to understand – patients will miss the chance for an early cure or treatment. The hazards of false positive tests, on the other hand, are more difficult to appreciate. As pointed out earlier, telling patient they have an illness (when they actually don’t) can have physical and psychological effects that are far more severe than the disease itself Furthermore, false positive tests often lead to a battery of expensive and unnecessary follow-up procedures.
Studies on the accuracy of screening tests should be done in the community-at-large because studies based in hospitals and clinics may tend to exaggerate accuracy. This is because hospitalized patients tent to have more advance illness which are, therefore, easier to detect.
- Cost effectiveness of the screening test, as well as treatment for the disease, should have been evaluated locally in properly conducted economic analyses.
Because effective screening tests must be performed on almost every healthy person, cost becomes a major concern. If economic resources were unlimited, then people could have any test done. Unfortunately, resource constraints exist in all countries – with no exception – and are felt at different levels. At the public level, money spent on screening could draw resources away from other health concerns such as treatment for tuberculosis and diarrhea. At the household level, money spent by a household on screening could divert precious resources from food, shelter and education. Because of this, for a screening test to acceptable, its cost (plus subsequent treatment for the disease detected) should be commensurate to the disease or complication that it is being prevented. Studies that evaluate costs, risks and benefits of treatment are called economic analyzes. Such studied need to be done locally because the costs of health interventions vary widely from country to country. Thus, findings of an economic analysis done in the United States should never be assumed to hold true in the Philippines or any other country, regardless of how thoroughly it was done.
Using these standard criteria, many Western countries have developed practice guidelines for periodic health examinations. The U.S. Preventive Services Task Force, for example, conducted an extensive evaluation of more than 200 tests that could potentially be performed for early disease detection among Americans.
The Canadian Task Force on Periodic Health Examination likewise formulated a health screening pan considered optimal for Canadians. As can be gleaned from these criteria, however, tests applicable in one country may not do well in another because of differences in disease prevalence, and differences in the price and availability of tests and treatments. Thus, it has become necessary to formulate recommendations on health screening for Filipinos, using the same stringent standards used by our colleagues in developed countries.
The decision to recommend or not to recommend a test should consider the interplay of the four factors above, rather than a single one. Nevertheless, few screening tests will satisfy all four criteria. To make the basis for the recommendations explicit, each recommendation in this book was graded according to the following scale:
Level 1 – recommendation satisfies all the above criteria.
Level 2 – recommendation satisfies #1 but not all of #2, #3, and #4.
Level 3 – recommendation satisfies #2, #3, and #4 but not #1.
Level 4 – recommendation satisfies none of the criteria