Terry Dyroff’s PSA blood test led to a prostate biopsy that didn’t find cancer but gave him a life-threatening infection.

In the emergency room several days later, “I didn’t sit, I just laid on the floor, I felt so bad,” said Dyroff, 65, a retired professor from Silver Spring, Md. “I honestly thought I might be dying.”

Donald Weaver was a healthy 74-year-old Kansas farmer until doctors went looking for prostate cancer. A PSA test led to a biopsy and surgery, then a heart attack, organ failure and a coma. His grief-stricken wife took him off life support.

“He died of unnecessary preventive medicine,” said his nephew, Dr. Jay Siwek, vice chairman of family medicine at Georgetown University. “Blood tests can kill you.”

Since Friday, when a task force of independent scientists said routine PSA testing does more harm than good, urologists who make a living treating prostate cancer have rushed to defend the test, as have patients who believe it saved their lives.

Less visible are men who have been harmed by testing, as Dyroff and Weaver were. The harm is not so much from the test itself but from everything it triggers — biopsies that usually are false alarms, and treatments that leave many men incontinent or impotent for cancers that in most cases were not a threat.

Once a PSA test suggests a problem, many men can’t live with the worry that they might have cancer. And once cancer is found, most men feel they have to treat it, usually at the urging of their urologist.

“There are many men who have had serious consequences from treatment. Those stories don’t get told and they are not uncommon,” said Dr. Len Lichtenfeld, deputy chief medical officer of the American Cancer Society, which thinks the task force reached “an appropriate conclusion” about the PSA test.

Many men who agree to a PSA test do not understand what it is. Some common misconceptions:

n It shows cancer. In fact, PSA is just a measure of inflammation, and it can be elevated for many reasons besides cancer: normal enlargement of the prostate with age, an infection, even recent sex, a strenuous bike ride or horseback riding.

n It’s been proven to save lives. Only two large, well-done studies have looked at this, the task force says. The American study found annual screening did not lower the chances of dying of prostate cancer. However, cancer fear is so great, and belief in the value of screening so ingrained, that half the men assigned to the group not offered PSA tests got one anyway. That made comparisons to the group given annual screening difficult. For that reason, some doctors don’t believe the study’s conclusion.

n It finds cancer early so you’re more likely to survive. About 90 percent of prostate cancers found through screening are early-stage. Most will grow so slowly they will never threaten a man’s life, but there’s no good way to tell which ones will. Research suggests that tumors causing symptoms are more likely to warrant treatment than those that are not. Also, finding aggressive prostate tumors early may not affect how lethal they prove to be; the PSA test may just let men learn of them sooner than they otherwise would.

“Most people tend to think ‘if it may help, I’m all for it.’ But we don’t know if it will help,” said Siwek, the Georgetown doctor whose uncle died.

The need to find a better screening tool is the real message from the task force, said Dr. Christopher Logothetis, prostate cancer research chief at the University of Texas M.D. Anderson Cancer Center in Houston. It may even be that there are better ways to use the PSA — employing it as a baseline test and tracking its rise over time — that might prove better than annual testing.