Scientists in the United States suggest a blood test widely used to screen for prostate cancer can be misleading in the case of men who are obese.
The researchers at Duke Prostate Center, Duke University in North Carolina, say doctors reading the results of a blood test commonly used to screen for prostate cancer can be deceived into thinking obese men are disease-free.
They say the test for a protein called prostate-specific antigen, or PSA, may in fact produce falsely reassuring results because obese people have more blood in their bodies and the concentration of the protein is diluted.
The prostate gland produces PSA and doctors use this to detect the presence of prostate tumors, if levels are higher it can be a sign of cancer; an enlarged prostate can also elevate PSA levels.
The discovery was made when the researchers examined the medical records of nearly 14,000 men who had undergone surgery to treat prostate cancer between 1988 and 2006.
The surgery was carried out at Johns Hopkins Hospital in Maryland, Duke University in North Carolina or five U.S. Veterans Affairs hospitals in California, Georgia and North Carolina.
The researchers found that men with a body mass index, or BMI, indicating obesity, had a higher blood volume and lower PSA concentrations.
The most obese men had PSA concentrations 11 to 21 percent lower than those recorded in men of normal weight.
The researchers say such men could have a total amount of PSA in the blood that might signal prostate cancer, but because they had so much more blood, the PSA concentration was so diluted that the test results seemed to show no cause for alarm.
Dr. Stephen Freedland, one of the research team says the PSA test needs to be adjusted by as much as 15 to 20 percent downwards for obese people or many cancers will be missed.
The prostate is a walnut-sized gland found below the bladder, which produces seminal fluid.