What Is a Screening Test?

Screening is a method of finding diseases in people who do not yet have any signs or symptoms of the disease being screened for. Although this idea sounds great, and we could ask: "Why don't we screen for all diseases?" the answer is quite complex. The goals of screening include helping people live longer, healthier lives. It is clear that although we could screen for many diseases, in a number of cases it is also clear that even if we find the disease we are screening for, the person does not benefit in any obvious way.

• Does screening improve health outcomes? Sometimes, a person diagnosed with the condition by screening seems to have no improvement in health when compared with a person who is only diagnosed when the disease eventually shows signs or symptoms. An example of a condition in which there is still some debate is diabetes. Although it is clear that there is probably some benefit from screening people with a strong family history of diabetes—usually by means of a blood test performed when the person has not eaten any food overnight—annual screening does not necessarily seem to be useful in the general population. Some doctors do advocate screening, but usually every 3-5 years.
  
  
• When does screening help? Screening helps when a test finds the disease or problem in a large proportion of cases. In other words, if you have the disease, and don't yet know it, there is a very good chance the screening test will pick it up. Equally, if you do not have the disease, there is a good chance that the test will not suggest that you might have it. An excellent example is blood pressure. The blood pressure cuff, if used correctly, is very accurate in diagnosing high blood pressure.
  
  
• What are the risks of screening tests? Surely a test designed to diagnose a disease cannot have any risks? In fact, there are a number of potential risks involved.
  
  
  • However accurate a test may be, there will always be someone who has the disease but does not get picked up by the test. These so-called false negatives can lead you to believe that you are healthy, when you are not.
    
    
  • The reverse event can also occur. You could be told that you have the disease when in fact you do not. These results are said to be false positives. The result may be that you have to undergo further tests, which may be more complex, not to mention expensive, just to be sure that you do not actually have the disease you were told you had.
  
  
• Are common tests more appropriate for some people? All these factors are taken into account before a test is regularly and widely used as a routine health test. These widely used tests are discussed here. Although many screening tests may be appropriate for everyone—blood pressure measurement, for example—some screening tests are more appropriate for certain groups of people.
  
  
  • Examples would be Pap smears and mammography for women, or regular bowel examination for people with a family history of bowel cancer.
    
    
  • The family history is very important to a doctor because it may point out tests that the doctor would perform in one case that may not be indicated in another person.
  
  
• What are the best or most reliable screening tests, and when should they be done? Among people in the Western world, a major cause of death is coronary artery disease. There are a number of risk factors for this condition. A risk factor is something that increases the chances of developing the disease if you have that factor, when compared with a person who does not have that factor. Some risk factors for heart disease include a family history of heart disease, smoking, high cholesterol, diabetes, and high blood pressure.
  
  
  • Some of these risk factors you cannot change. You cannot change family history, for example.
    
    
  • Some risk factors are completely under your control. You can determine whether to alter that risk factor—stopping smoking is one example.
    
    
  • Some factors could be altered through medication, dietary control, exercise, or other means, if only you knew that you had that risk. Examples are high blood pressure and high cholesterol.