False positive

My daughter wanted to know about false-positive tests this week. She's a fan of the TV medical drama, House, so I caught a bit of it while I was doing the dishes (you'll have to take my word for it).

An oncologist had to break some disturbing news to a patient. Of course, there was a twist.

The man had been diagnosed with terminal lung cancer, but it turned out that the test was incorrect, i.e false-positive. He didn't have cancer at all. The oncologist expected that the man would be thrilled to hear the news. He wasn't.

The oncologist couldn't understand why the man was upset. Surely he should be overjoyed at having his life sentence lifted!

The problem was that the man had already acted on the false report. He had told his friends the bad news. He had sold his house and spent the money on a trip to Europe. While he was happy that he didn't have cancer, he was not pleased with the profound effect this false alarm had on his life.

A similar situation comes up very commonly in urology practice. Men are often tested for prostate cancer using prostate-specific antigen (PSA). Well, at least they think they're being tested for prostate cancer. The PSA blood test doesn't actually give a yes-or-no answer to this question. It just tells us how suspicious we should be and whether further testing is warranted. The higher the PSA level, the greater the likelihood that prostate cancer is present.

But there's a twist here, too.

Benign prostate enlargement - very common in men over age 50 - also causes the PSA level to rise. In fact, when the PSA is mildly elevated (for example, between 4 and 10), it's more likely that the elevation is due to benign disease rather than cancer, in a 2:1 ratio. That's a lot of false-positives.

The abnormal PSA level leads to further testing, usually a prostate biopsy. This involves inserting a probe into the rectum and using a needle to take samples of the prostate. It's uncomfortable and carries some risk of complications. Also, men with abnormal PSA levels suffer anxiety about the possible cancer diagnosis.

When there is no cancer present (i.e. the PSA level was up because of benign prostate enlargement), the man goes through a needless biopsy and worry. Yet, when I call men about their negative biopsy results, they universally say "Whew, that's good news."

I sometimes wonder why they don't react like the patient on House: "You mean I went through all that worry and that biopsy done for nothing? I never had a problem in the first place. If I hadn't had that PSA test done, I could have been spared all of this. That test was a false alarm!"

When a false-positive test comes back, it means we've taken a healthy person (well, at least, they don't have that particular disease) and put them through stress and further testing that is of no value to them. Many people rationalize this with the old "Better safe than sorry" argument.

Of course, it's up to each man to decide whether he wants to take the chance of having a false-positive result. That means he should be informed of the risks and benefits of PSA screening before being tested. My experience is that most men haven't been informed before testing. Many of them aren't even aware the test was done (usually as part of "routine blood work") until they're called with the abnormal result.

"Better safe than sorry" only holds true if the patient has had the chance to consider how much "sorry" they're willing to accept to be "safe".