A high PSA level doesn’t necessarily mean you have prostate cancer, and men who have a normal PSA level – a 4 count or below – may still have cancer after all, according to a large study.

Men over the age of 50 usually get prostate-specific antigen blood tests, but doctors are now saying PSA levels are not the best indicators for whether or not a man has prostate cancer.

A high PSA level may only mean cancer is brewing, or the prostate is enlarged, but not cancerous. It could also indicate an infection. And screening often detects small tumors that prove too slow-growing to be deadly.

Dr. Andrew Vickers of Memorial Sloan-Kettering Cancer Center in New York City, said how fast the PSA level rises is something that men and doctors “worry a lot about.”

“Men show up here with a PSA of 2, and we say, ‘Why are you here?’ and they say, ‘Well, I used to be a 1, and my doctor’s worried. Am I going to die?’”

So Sloan-Kettering researchers studied whether considering PSA velocity adds value to the biopsy-or-not decision in those otherwise low-risk men — and concluded it doesn't.

"This is a really important study," said Dr. Otis Brawley of the American Cancer Society, who wasn't part of the research. "A lot of doctors are going to stop looking at a PSA rise of 1 and ordering biopsies."

Vickers' team tracked 5,519 men who'd taken part in a huge prostate cancer prevention study and who'd received a biopsy at the study's end regardless of their PSA level.

Just having a rising PSA — if nothing else was considered — was associated with a slightly higher risk of having cancer, although not the more worrisome aggressive kind. But the PSA level alone, not its rise, was a much better predictor of a tumor, reported Vickers, a statistician who specializes in prostate cancer.

Focusing on PSA's rise instead triggered many more biopsies, with close to 1 in 7 men who would get one, concluded the study, published Thursday in the Journal of the National Cancer Institute.

That compares with 1 in 20 men who are biopsied for a high PSA level alone, noted Dr. Grace Lu-Yao of the University of Medicine and Dentistry of New Jersey in an accompanying editorial.

"There's an important public health message here, which is for men not to worry about changes in their PSA if their overall PSA level is low," Vickers said.

The Associated Press contributed to this article.