Obesity and Screening PSA Levels Among Men Undergoing an Annual Physical Exam

Background: Prior reports suggest that obesity is inversely associated with screening prostate-specific antigen (PSA) levels and may reduce screening sensitivity.

Methods: We evaluated data on 10,623 men screened for prostate cancer during an annual physical examination program administered by EHE International, Inc., between 1/1/2004 and 6/30/2006. Of these, 3,623 men returned for additional physical exams during this period. We used multivariate linear regression analyses to determine whether higher BMI was inversely associated with PSA, and whether BMI, or change in BMI, was associated with change in PSA levels over time. We also developed a theoretical model for the effect of obesity on PSA levels in which increased plasma volume in the obese dilutes PSA levels.

Results: After control for age and race/ethnicity, higher BMI was associated with lower PSA levels; men with a BMI > or =40 had a geometric mean PSA level 0.14 ng/ml lower than men with a BMI <25 (P < 0.001). Prospectively, BMI at initial screening and change in BMI over 2 years were not associated with change in PSA or PSA velocity. Our theoretical model accurately predicted observed PSA levels and suggests that a screening PSA of 4.0 ng/ml in normal weight and overweight men corresponds to 3.5 ng/ml in obese men and 3.1 ng/ml in morbidly obese men.

Conclusion: Across the study population, increased BMI was significantly inversely associated with lower PSA. Based on a theoretical model in which increased plasma volume in the obese dilutes PSA levels we propose new cut-points for a positive screening test.