Obese white men are about half as likely as normal-weight white men to have a total PSA level of 4 ng/mL or higher, a commonly used criterion for recommending a prostate biopsy, according to investigators.

As a result, tumors of obese men are more likely to be detected later in the disease course, the investigators noted in BJU International (2009; published online ahead of print).

This possibility, they observed, is consistent with findings of previous studies demonstrating that obese men with prostate cancer have worse tumor features and oncologic outcomes. The lower likelihood of an abnormal PSA test result in obese men also is consistent with prior research showing a lower overall incidence of prostate cancer in obese men.

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The findings, by Stephen Culp, MD, PhD, and Michael Porter, MD, of the University of Washington in Seattle, are based on an analysis of data from 3,152 men who participated in the National Health and Nutrition Examination Survey (NHANES) conducted over the years 2001-2002, 2003-2004, and 2005-2006. NHANES is a nationally representative sample of noninstitutionalized individuals aged 20 years and older.

For this study, the researchers excluded men with PSA levels of 20 or above under the assumption that they were likely to have prostate cancer detectable by digital rectal examination. Drs. Culp and Porter used PSA thresholds of 2.5 and 4 to categorize PSA values as normal or abnormal.

The study revealed an inverse association between BMI and the likelihood of having a PSA level of 4 and higher in white non-Hispanic men. Obese men (BMI 30-39.9 kg/m2) had a46% lower risk of having an abnormal PSA test result compared with men who had a normal BMI (18.5-24.9). The researchers observed no association between PSA and BMI when they used a PSA threshold of 2.5.

If PSA screening is to be applied with equal effect to men with differing BMI, the authors wrote, perhaps PSA should be corrected for BMI, akin to how PSA is interpreted differently based on patient age or how PSA values are corrected in men who chronically use 5α-reductase inhibitors for symptomatic BPH.

Nearly two years ago, researchers published a report in JAMA (2007;298:2275-2280) suggesting that obese men may have lower PSA levels because they have higher circulating plasma volumes than nonobese men, resulting in hemodilution of PSA.