To Screen or Not to Screen…
Screening for disease. It makes sense to try to find a disease before symptoms arise. Unfortunately not all diseases or conditions lend themselves to screening, and not all screening tests offer the same value.
Inappropriate screening can lead to over-diagnosis or mis-diagnosis with a false positive test. That can lead to further testing , anxiety, interventions such as (needless) surgery, and of course cost. In other cases screening may lead to a false sense of security with false negatives, reassuring patients they are safe when they may not be. And the test itself may be painful, invasive or costly.
One successful screening test is the pap smear, the test for cervical cancer. Cervical cancer used to be the leading cause of death in women in the United States, but over the last 40 years the death rate for cervical cancer has declined by 70%, mostly attributable to the pap. The test is done by directly collecting cells from a woman’s cervix (part of her uterus) during a routine pelvic exam. The test, while invasive, can be included in a routine exam, causes little or no discomfort and is inexpensive. Early, developing cervical cancer can cause changes in the cells long before true cancer arises, creating a window of opportunity to intervene and prevent disease, the loss of the uterus or of the woman’s life. Finally, the test can be done at long intervals: every 3 years from ages 21-29, every 5 years from 30-65 if all tests are normal.
That’s a great screening test.
The PSA test, or prostate specific antigen, a measure of the hormone a man’s prostate secretes, is not a great test for screening.
PSA screening is at best controversial and at worst dangerous. The prostate secretes this hormone under a number of settings. A high level does not always mean cancer and a low level does not always mean cancer-free. The test itself is not consistent and can vary from lab to lab. The risk of false positives, over-diagnosis and the subsequent harms (infertility, incontinence, death) far outweigh the chances of preventing even one case of prostate cancer in 1,000 tests.
For these reasons the USPSTF (United States Preventive Services Task Force, the government agency charged with preventive health care testing and management for the nation) does NOT recommend PSA screening routinely in asymptomatic men.
Still PSA testing has some utility: a significant increase over time (testing every 3-5 years for example) can be a clue to the development of disease. And it can guide for or against further investigation in the patient with symptoms such as bloody urine or pain. So PSA testing, under guidance, can still be useful.
Screening is a tool, not a cure. Screening becomes most valuable when done in the setting of ongoing preventive care. The test alone does not always indicate disease; it needs to be taken into context with the patient’s entire health and life history.
Remember there are very few instances when a single test makes a diagnosis. Work together with your family doctor (or other provider) to prevent disease or find them early.