1. What is your opinion on the PSA test for prostate cancer?
The PSA test measures the blood level of Prostate-specific antigen, a protein produced by the prostate gland. The higher a man's PSA level, the more likely it is that he has prostate cancer. However, there are additional reasons for having an elevated PSA level, and some men who have prostate cancer do not have elevated PSA. So, it is not a perfect test. The PSA test has been widely used to screen men for prostate cancer. However, some advisory groups now recommend against the use of the PSA test to screen for prostate cancer because the benefits, if any, are small and the harms can be substantial. None recommend its use without a detailed discussion of the pros and cons of using the test. [Source: http://www.cancer.gov/cancertopics/factsheet/detection/PSA ]
2. How do you evaluate a diagnostic test for a condition that is difficult to diagnose, and no "gold standard" is available?
There are many conditions where a 'gold standard' does not exist (examples include depression, irritable bowel syndrome, dementia, attention deficit disorder). In such situations, we evaluate a new diagnostic test by comparing it against a 'composite reference standard' that is made up of several tests and clinical data. Response to treatment can also used to decide on final diagnosis. Lastly, there are some statistical models that can account for imperfect gold standards.
