What Screening Tests are For

Avoiding Health Risks
May 15, 2012
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May 19, 2012

Many people wonder why doctors take so much blood or why they order so many tests. They worry that there must be something wrong with them and wait for the test results with trepidation. What doctors often fail to tell the patients are that most of these tests are just screening tests and that they are well until proven otherwise. Screening tests have a big role in medicine and patients need to understand why doctors do them and what the benefit is to them.

Screening tests are often done for detection of cancer. They are done so that, if early cancer is present, it can be found before it becomes advanced cancer and so it can be treated with the best chance of success. Some cancer screening tests include a chest x-ray, colonoscopy and mammography. There are regular schedules for doing these things and a test for cancer doesn’t mean you have cancer.

Doctors also screen for diabetes, in part because its incidence is increasing. The most common screening test for diabetes is a fasting blood sugar (glucose). If the screening test shows higher results, more tests such as HbA1C and Oral Glucose Tolerance Test can be done to confirm the diagnosis of diabetes.

Some screening tests are very accurate. For example, if you are screened for HIV and come up positive then most likely, you have HIV. The false positive rate for this test is very low. On the other hand, some screening tests just mean you need more testing. This is especially true for tests like mammography. The mammogram is done to see if there are any abnormalities and tells the doctor whether or not further testing, such as a biopsy, needs to be done. This kind of test is neither accurate nor precise.

A screening test basically tells the doctor who is at higher risk for the disease and who needs to stay on and undergo further testing. Screening tests are designed to be done on large populations of people and have a degree of false negativity and false positivity. Having a positive screening test, especially one that turns out to be a false positive, can be very frightening for the patient. They can spend several days thinking they have a disease only to find out in further testing that no disease is present. The anguish and suffering in such cases cause some people to avoid having screening tests altogether.