A digital rectal exam (DRE) remains an important part of screening men for prostate cancer because it can find some prostate cancers even when the more popular PSA test is normal, new research confirms.

In a digital rectal exam, the doctor inserts his or her gloved finger into the rectum. Because the rear of the prostate gland lies just in front of the rectum, the doctor can feel any irregularity of the gland’s surface.

Aldo A. Ghobriel, MD, of the University of Texas Health Science Center in San Antonio, presented his findings at the recent annual meeting of the American Urological Association in Orlando, Fla.

"Our study data confirm that the DRE is still of clinical significance, even when PSA levels are well within the normal range, all the way down to one [nanogram per milliliter]," said Ghobriel.

Like most cancers, prostate cancer is most likely to be treated successfully when found in its early stages.

But early-stage prostate cancer usually doesn't produce any symptoms, so the American Cancer Society (ACS) recommends doctors offer men the option of yearly screening tests for the disease using two tests, the DRE and the PSA, along with a discussion of the benefits and risks of the tests.

The ACS says doctors should start offering such screening at age 50 for most men, and screening should start at age 45 for African-American men and those at high risk because of a family history of the disease.

With the DRE, the doctor feels for a lump on the prostate gland or for any other abnormality.

The PSA test checks blood levels of prostate specific antigen (PSA), a protein produced by the prostate gland. PSA levels below four (nanograms per milliliter) are considered normal, but above that, doctors may recommend a biopsy.

Many doctors feel if the PSA is low, then there is little chance that cancer is present and may not advise a biospy. A biopsy removes a small amount of prostate tissue through a needle for exam under a microscope. This is the only way to be certain whether prostate cancer is present.

Ghobriel and his colleagues looked at the records of 971 men who had prostate biopsies for suspected prostate cancer in 1999 and 2000, dividing the men into four groups according to their PSA levels.

In men with abnormal DRE tests, biopsy found prostate cancer in about 4% of those with PSA lower than one, in about 17% of those with PSA between one and two and one-half, and in about 26% of those with PSA between two and one-half and four.

That means that if those men or their doctors had skipped the DRE and relied on the PSA test alone to decide whether the men should have a biopsy, their prostate cancer might not have been found until later.

And many with PSA between one and four who did have cancer had an aggressive variety of the disease.

Among those with abnormal DRE tests, only those with PSA lower than one could safely have gone without a biopsy, because only about 4% had cancer, and none had an aggressive variety, which may be more likely to grow quickly and spread, said Ghobriel.

"This study clearly shows that while the PSA test is a good tool, it is not a perfect tool, and by combining it with a DRE, we can significantly increase the likelihood of detecting abnormalities, including cancer," said Durado Brooks, MD, director of prostate and colon cancer control for the ACS.

Finding prostate cancer before it produces symptoms can involve both risks and benefits, said Brooks. For that reason, the ACS recommends that men have a thorough and open discussion with their doctors before deciding whether to take prostate cancer screening tests, and how often, and how to interpret them.

But for those men who choose the advantages of early detection, this study confirms that two tests — the DRE and the PSA — are better than one, said Brooks.