RISKS AND BENEFITS OF SCREENING
False positive means that a person is found to be positive on the initial screening test for the condition being sought, but does not actually have that condition. For example, if cardiac stress tests are given to 18 year old military recruits, a small but significant number of them will have abnormal tests. Upon further testing the majority of these individuals will be found to be perfectly fine. They will have gone through the emotional upheaval of having a possible serious medical condition and the inconvenience, expense, and occasionally danger of more sophisticated evaluation.
False negative means that the person really does have the condition being tested for, but the initial screening test is negative. That person will now have a sense of reassurance that he is fine, but in fact is a victim of the disease. This can often result in a delay in diagnosis and treatment.
There is no 100% absolutely perfect test. All tests have a certain False Positive and False Negative rate.
Medical experts will often argue over when to apply or recommend a test based on the characteristics above, as well as whether the condition is sufficiently common or serious to warrant widespread testing.
Be aware that based on updated evidence, GUIDELINES MAY CHANGE over time and be altered. For instance, recommendations on screening Pap Smears, breast self- exams, PSA testing, and mammography are an evolving field.
It is possible to find conditions for which no effective treatment exists. There are conditions where the condition may be found earlier, but follow up studies do not show any benefit as compared to persons who were not screened. That is, you can find the condition but it does not make any difference to find it earlier instead of later.
It is also possible to find conditions for which no treatment would be necessary. For instance, it is unlikely that one would treat asymptomatic prostate cancer in a 100 year old man who is comatose in a nursing home.