Abstract: Objective To determine the effect of obesity on prostate specific antigen (PSA) in men with benign prostatic
hyperplasia (BPH) and develop a PSA-related parameter that can eliminate the effect of obesity. Methods We reviewed the
clinical data of 706 patients with BPH. Two PSA-related parameters, namely PSA mass (total circulating PSA protein) and PSA
mass ratio (total circulation PSA protein per prostate volume), were calculated for all the patients and the association of BMI
with PSA, PSA mass, and PSA mass ratio was assessed. Results A higher BMI was significantly associated with a greater
plasma volume and prostate volume (P<0.05). Linear regression analysis revealed a greater adjusted R2 of BMI versus plasma
volume than of BMI PSA (0.569 vs 0.027). PSA was positively associated with the prostate volume and negatively with BMI and
plasma volume (P<0.05). PSA mass was positively associated with prostate volume (P<0.05) but was not associated with BMI or
plasma volume (P>0.05). PSA mass ratio was not associated with prostate volume (P>0.05) but negatively associated with BMI
and plasma volume. Plasma volume and prostate volume, PSA, and PSA mass ratio (P<0.05), but not PSA mass (P>0.05),
differed significantly among normal-weight, overweight, and obese patients. Conclusion A higher BMI is associated with a
greater plasma volume in BPH patients. In obese patients with BPH, a lower PSA concentration may result from hemodilution
caused by a greater plasma volume, and PSA mass can eliminate the effect of obesity on PSA.