[This is the final part of a three-part series on the PSA test for prostate cancer.]

Cancer of the prostate is one of the most common types of cancer among American men. More than 6 in 10 cases of prostate cancer cases occur in men 65 and older. Treatment for prostate cancer works best when the disease is found early.

Prostate-specific antigen (PSA) is a protein produced by the cells of the prostate gland. The PSA test measures the level of this protein in the blood. It can be detected at a low level in the blood of all adult men.

A fundamental problem with the PSA test is that, while elevated levels can indicate the presence of cancer, they can also be caused by other problems such as benign enlargement of the prostate that comes with age, infection, inflammation and seemingly trivial events such as ejaculation and a bowel movement.

PSA test results are horribly confusing and often terrifying. In the first parts of this series, we discussed the sources of much of the confusion. In this column, we’ll address the primary question about PSA: Does it save lives?

The answer is: We don’t know. What’s worse is that we don’t know if PSA screening outweighs the risks of follow-up diagnostic tests and cancer treatments.

For example, prostate surgery can cause incontinence and erectile dysfunction. Even a  prostate biopsy has risks because it can cause bleeding and infection.

The PSA test can detect small tumors. However, finding a small tumor does not necessarily reduce a man’s chance of dying from prostate cancer. PSA testing may identify very slow-growing tumors that are unlikely to threaten a man’s life. Also, PSA testing may not help a man with a fast-growing or aggressive cancer that has already spread to other parts of his body before being detected.

So, what should a man do to protect himself from prostate cancer?

Some doctors encourage annual screenings for men older than age 50; others recommend against routine screening. However, most doctors and medical organizations agree that men should learn all they can about prostate cancer, so they can reach informed decisions.

My personal history with PSA tests is illustrative of many of the problems men face with this type of screening. I hope that sharing it will help.

I’m 69 years old. I’ve been having physical exams almost every year since I hit my 50s. These physicals included a PSA blood test and a digital rectal exam (DRE).  Until recently, all tests produced normal results.

My PSA was always around 1.5. Most doctors want your PSA to be under 4. (The numbers stand for nanograms of PSA per milliliter of blood.) And, my DREs found no irregularities, just some benign enlargement.

About three years ago, my family physician gave me a DRE and found nothing, but my PSA test came in at 2.97. My doctor told me to see a urologist for a follow-up exam because my PSA, while under 4, had increased.

The urologist did another DRE and ordered another PSA test. The test came in at 2.96. The urologist said that he thought 2.96 was my new PSA and that I should not worry about it.

Two years later, my PSA was still 2.96. Then, this year, it came in at 4.1.  My family physician sent me to a urologist.

Before I went to the urologist, I did some research and learned that something as seemingly insignificant as a bowel movement could affect a PSA test. I told the urologist that I recalled going to the bathroom just before having blood drawn. He thought that this BM could have affected the test.

Another DRE. Okay. Another blood test. The PSA was 3.3. The urologist said no biopsy was required. The increase from 2.96 to 3.3 was not a cause for concern.

What now? I’m tempted to forget about PSA tests, but I’ll probably have another in a year.

The Healthy Geezer column publishes each Monday on LiveScience. If you would like to ask a question, please write fred@healthygeezer.com. © 2010 by Fred Cicetti.