Warren Buffett's decision to undergo prostate cancer screening reflects the reality that nearly half of American men 75 and older continue being tested despite official  recommendations against doing so, researchers reported today.

"PSA screening for more than 40 percent of men 75 or older is inappropriate," said Dr. Scott G. Eggener, an assistant professor of surgery at University of Chicago Medical Center, whose research confirms that older men aren't heeding 2008 guidance from the U.S. Preventive Services Task Force.

"Selective screening is reasonable to consider for the healthiest men over age 75, but for the large majority of men in this age group, early detection can lead to treatment of a disease that will probably never cause a problem," he said.

In 2008, the USPSTF issued a recommendation that found limited benefit for screening men ages 75 and older for prostate cancer. Last year, the task force drafted guidelines that said prostate screening was of limited benefit for helping men of any age live longer, and that harms of unnecessary treatments often outweigh benefits.

Eggener and his colleagues set out to determine whether men were paying attention to the guidelines. They found that in 2005, two years before issuance of the guidelines, 43 percent of men 75 and older underwent prostate-specific antigen (PSA) testing, which measures levels of a protein in the blood.

In 2010, when the guidelines had been out for two years, the screening rate among those men rose slightly to 43.9 percent, according to results appearing in this week's issue of JAMA.

Last week, Buffett, the 81-year-old CEO of Berkshire Hathaway, announced that he would undergo radiation treatment beginning in mid-July for Stage 1 prostate cancer, and that a CT scan, bone scan and MRI found no evidence it had spread.

At the time, top U.S. urologists and prostate surgeons reacted to the announcement by saying that most men with newly diagnosed prostate cancer are likely to die from something else.

However, there are exceptions, as world-renowned prostate cancer expert Dr. Patrick Walsh, a urology professor at Johns Hopkins Medical Institutions in Baltimore, pointed out to ABC News, citing a University of Rochester study appearing last year in the journal Cancer that found half of the deaths from prostate cancer "occur in men who are diagnosed after the age of 75."

"The fact is that older men who are diagnosed with prostate cancer oftentimes have more advanced disease than younger men - the opposite of what we used to believe," Walsh said.

Some older men can have aggressive Stage 1 tumors, which despite being confined to the prostate gland, contain highly abnormal cells capable of spreading quickly, Walsh said.

Dr. William J. Catalona, director of the Clinical Prostate Cancer Program at Northwestern University in Chicago, told ABC News that Buffett's case "shows how valuable the PSA test is, especially in view of a rumor I heard that the USPSTF will probably release its final recommendation against PSA screening in the next few weeks."

Catalona described PSA testing as "the most effective way to detect prostate cancer in its curable stages and if used intelligently it reduces the chances of dying from prostate cancer by nearly 50 percent. Warren Buffett is no dummie."

Eggener and his colleagues reviewed cancer data from the National Health Interview Survey, which follows a representative group of 87,500 Americans. They focused on men aged 40 and older who said they underwent prostate cancer screening as part of a routine exam. Screening rates were unchanged between 2005 and 2010 in all age groups, Eggener and his colleagues reported. They found PSA screening more common among men 75 and older than those 40 to 49 and 50 to 59.

The study authors said their data likely underestimated the rate of men underdoing PSA testing, because self-reports are lower than rates found when researchers review actual medical records.

They recommended monitoring of the effect of the 2011 USPSTF recommendations.