Hemodilution may explain lower levels in obese men.
Obese men without prostate cancer have lower prostate-specific antigen (PSA) concentrations than normal-weight men without prostate cancer, and obese men with prostate cancer have poorer outcomes than normal-weight men with prostate cancer. Investigators explored a possible connection between these two observations by studying PSA levels in 13,634 men (mean age, about 60) from three cancer cohorts; all had prostate cancer, diagnosed by needle biopsy prompted by elevated PSA level, and all had undergone radical prostatectomy.
Men were excluded
if they received preoperative hormone therapy, radiation, or chemotherapy or if
they had positive lymph nodes. Based on standard body-mass index and plasma
volume calculations, 24% of the sample was obese (BMI 
30
kg/m2), and roughly 36% had Gleason scores of 7 or higher. In
multivariate adjusted analysis, higher BMI was significantly associated with
lower PSA level. Men with BMIs 35
had 11% to 21% lower PSA levels and 21% to 23% larger plasma volume than
normal-weight men. Overall, there was no association between weight and prostate
mass.
Comment: These mostly retrospective data suggest that PSA hemodilution may explain why obese men have lower PSA levels than normal-weight men. This hemodilution might lead to delayed diagnosis of prostate cancer, which in turn might be clinically important if studies eventually show that PSA screening reduces prostate cancer mortality. A prospective, longitudinal study tracking PSA levels and diagnosis relative to weight is appropriate.
Published in Journal Watch General Medicine December 4, 2007
Bañez LL et al. Obesity-related hemodilution and PSA concentration among men with prostate cancer. JAMA 2007 Nov 21; 298:2275.