MONDAY, Dec. 12, 2005 (HealthDay News) -- A prostate cancer test that measures changes in prostate-specific antigen (PSA) over time is sensitive to lifestyle and demographic factors that can skew the results, a new study found.
The multiple screenings -- known as "the PSA velocity" test -- to assess PSA level rate changes, differ from the traditional once-a-year PSA test.
"Unlike PSA, which is a pretty good test if it's used appropriately, PSA velocity has not been examined with the same degree of scrutiny, and the velocity appears to be affected more by lifestyle variables," said study co-author Dr. Ian M. Thompson, of the department of urology at the University of Texas Health Science Center at San Antonio.
PSA blood tests screen for abnormally high levels of PSA, which can indicate the risk of new or recurring prostate cancer.
The American Cancer Society recommends that healthy men aged 50 and older undergo yearly PSA blood tests, along with a digital rectal exam. High-risk patients -- including blacks and men with a father, brother or son diagnosed with prostate cancer before the age of 65 -- are encouraged to begin testing at age 45.
Thompson and his colleagues noted that a decade-plus decline in prostate cancer mortality rates among American men suggests that such advice is being widely heeded.
They said that in 2002, more than 75 percent of American men over the age of 50 reported having had at least one PSA test, while almost 60 percent said they had undergone testing within the prior two years.
However, the researchers also noted that non-cancer-related factors -- such as prostate infections, benign prostate enlargement, certain medications and age -- can sometimes contribute to elevated PSA counts.
A growing concern over such false-positive PSA readings for prostate cancer -- which can lead to unnecessary medical procedures including biopsies -- have prompted scientists to explore new, potentially more accurate ways to interpret PSA levels.
The PSA velocity test, a multiple test alternative to the traditional yearly snapshot reading, has been touted by some experts as one potential answer to accuracy concerns.
Looking at both traditional and velocity PSA testing, Thompson and his colleagues assessed the influence that outside factors have on accuracy by reviewing PSA readings among 3,341 healthy, primarily white men over the age of 55.
Seven years of digital rectal exam and PSA testing, followed by biopsies, had revealed that none of the men had prostate cancer.
Demographic information was reviewed for all the men, including race, age, diet, smoking habits, supplement use, height, weight, body mass index and physical activity habits.
Reporting in the Jan. 15 issue of the journal Cancer, the authors said that non-cancer-related factors do appear to have some influence on all PSA readings.
PSA velocity numbers were found to be 38 percent higher among black men than white men, but lower among men who routinely took high-dose calcium supplements. Velocity numbers also came in 33 percent lower among smokers than non-smokers.
Comparing the traditional PSA exam with velocity PSA testing, the authors noted that the snapshot PSA tests revealed significantly higher average PSA levels as men aged -- with men over 70 having PSA levels that were 22 percent higher than those among men between 55 and 59 years of age.
Also, PSA values dropped in once-yearly tests as body mass indexes rose, but were not strongly affected by specific dietary habits.
PSA velocity numbers, on the other hand, dropped as men got older.
Thompson and his colleagues concluded that once-yearly PSA tests -- while affected by external factors -- would probably not be affected to the point of being unreliable.
However, they suggested that PSA velocity testing is much more sensitive to non-cancer-related factors and could, therefore, be unduly subject to misinterpretation and misdiagnoses.
"A lot of doctors are applying PSA velocity as if it's gospel, and they should be careful of that because a lot of things can influence the change in PSA velocity," Thompson said. "It's not just cancer that can affect PSA velocity."
Dr. Durado Brooks, director of prostate and colorectal cancers at the American Cancer Society, described the study findings as interesting, but not a harbinger of imminent change regarding the way PSA tests of either kind are administered or read.
"It does give physicians a little information as to how to make assessments in terms of PSA velocity," said Brooks. "But I think the impact on patients is very limited. It really raises a lot more questions than it does provide answers. So I don't think it will significantly alter the way PSA abnormalities will be addressed at this time."
More information
For more on PSA testing, visit the American Cancer Society.
