Last Updated: 2003-07-02 11:00:27 -0400 (Reuters Health)

NEW YORK (Reuters Health) - It's good news for middle-aged male bike riders: riding to your doctor's appointment will not affect the results of a blood test for prostate cancer, new research suggests.

European investigators found that levels of the protein prostate specific antigen (PSA) did not vary in blood samples taken before and after men completed a 13-mile bicycle course.

PSA is a protein produced by the prostate gland, and elevated levels in the blood can signal prostate cancer.

However, the PSA test is somewhat unreliable: an increase in PSA does not always indicate cancer, and cancer can occur without a rise in PSA.

PSA blood levels also rise and fall as a result of numerous factors, such as age or inflammation of the prostate. Indeed, research suggests that the concentration of the protein in the blood of a healthy man can vary by as much as 30 percent.

The current study, published in the journal Urology, suggests, however, that the combination of exercise and pressure placed on the prostate -- features of bike riding -- should not be added to the list of factors that influence PSA levels in the blood.

"According to the results of our study, cycling has no impact on PSA-based screening for prostate cancer," write Dr. Hans-Joachim Luboldt of the University Hospital Essen in Germany and colleagues.

During the study, the researchers measured PSA levels in 33 men between the ages of 50 and 74 right before a bike ride and one hour after.

They found there were no significant changes in the levels of PSA from before and after the bike ride.