New research published Tuesday shows that prostate cancer screening may be affected by certain consequences of obesity, thus misleading doctors when they read test results.

Researchers from the Duke University Medical Center in Durham, N. C. published a study in the Nov. 21 issue of The Journal of the American Medical Association based on their analysis of medical records belonging to nearly 14,000 men.

Lionel L. Bañez, M.D., and colleagues write that tests devised to identify prostate cancer may be misleading in obese patients; due to their weight, these patients have more blood, which dilutes the specific protein used to detect the presence of prostate tumors, reports Reuters.

The researchers looked at the medical records of nearly 14,000 men who had undergone prostate cancer surgery between 1988 and 2004, either at Johns Hopkins Hospital in Maryland, the Duke Prostate Center in North Carolina or five U.S. Veterans Affairs hospitals in California, Georgia and North Carolina, according to Reuters.

They found that obese men, with a high body mass index (BMI), had a higher blood volume and lower concentrations of prostate-specific antigen (PSA), a protein produced specifically by the prostate gland; high levels of PSA are a possible sign of cancer.

The researchers reported that the most obese men had PSA concentrations 11 to 21 percent lower than those recorded in men of normal weight; while these men could have a total PSA level that could signal cancer, the additional blood diluted the protein’s concentration and tests failed to signal possible risk of cancer.

This means that while detecting a low PSA level in a thinner man can signify good prostate health, it could be a sign of concern in an obese one.

One of the researchers involved in the study, Duke urologist Dr. Stephen Freedland, told the news agency: “It's not that PSA is a bad test in obese men. Rather, we just need to learn how to use it better…. whatever (PSA level) you consider abnormal, you just have got to adjust it by about 15 to 20 percent downwards for obese people.”

The prostate gland is a walnut-sized gland located in front of the rectum and underneath the urinary bladder. Prostate cancer is the most common cancer, other than skin cancers, in American men, according to the American Cancer Society, which estimates that during 2007 about 218,890 new cases of prostate cancer will be diagnosed in the United States.

The ACS estimates that 27,050 men in the United States will die of prostate cancer in 2007.