Tuesday, February 22, 2005

Screening tests

RangelMD has a great site and I recommend you keep current on it. Recently he posted on Misleading ads for whole body scans. I agree with him that this is not an effective screening tool. In order to be effective as a screen, a test must meet certain criteria:
  • The test must be able to detect the disease at a stage early enough to make a difference in the outcome. Example: bimanual pelvic exam for ovarian cancer. This test can detect the disease, but by the time the cancer has progressed enough to be palpable, it cannot be treated successfully.
  • The test must be acceptable. Bilateral mastectomy or oophorectomy or prostatectomy would detect the respective cancers, but would not be acceptable (or cost effective.)
  • The treatment must be less morbid than the disease. Example: Many patients would choose not to treat cancer with radiation and chemotherapy if this will not result in a significant extension of life.
  • When applied to a large enough population, the cost of the test must be acceptable to society as a whole. In other words, the cost per year of life saved after treatment must be acceptable. This includes the cost of negative work-ups for false negative tests. There is also the psychological cost of telling a patient that he has a positive scan and then the confirmatory testing is negative.
  • The test must be sufficiently sensitive and specific.
In addition, the disease must be prevalent enough in the population to make detection reasonable. It would not be useful to test for sickle cell disease in Northern Europeans.

So, while whole body CT may be effective in detecting certain diseases, the evidence is mounting that it is not an effective screening test.

Another thought:
In my community, patients can access these scans without a physician's order. There is not specific physician responsible for the f/u of any positive results. What happens to the patient with a lung mass who doesn't get f/u? Who gets sued?

I remember when I was doing OB and patients would ask for an ultrasound "just because." It got to the point where it was an expected part of being pregnant, and not just a test that was done for specific indications. The patients would often ask for a video of the ultrasound. There were people in the community who were doing ultrasounds at the patient's home just to provide a tape. My group was very nervous about this. The patients did not realize that there was no reassurance associated with these ultrasounds, that they were being provided for entertainment purposes only. Several of my partners were presented with these tapes and asked to review them to "make sure my baby's OK."