US Pharm. 2008:3(2):HS-34. 

A blood test for prostate-specific antigen (PSA) levels remains a key diagnostic tool in the diagnosis of prostate cancer. And while many physicians will readily admit that the test is not perfect, they may now have to contend with another variant that could have a compromising effect on the PSA test result.

According to a study published by Lionel Banez, MD, and colleagues in JAMA, higher body mass index (BMI) may adversely affect the PSA number by falsely lowering it. Previous studies showed that obese men have lower PSA concentrations than nonobese men. But the authors found that "men with higher BMIs also have larger plasma volumes, which could decrease serum concentrations of soluble tumor markets--a phenom!=enon known as hemodilution."

The researchers found that higher BMI was significantly associated with greater plasma volume in all study populations. Men with a BMI of 35 or greater had 11% to 21% lower PSA concentrations relative to normal-weight men.

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