Serum Prostate-Specific Antigen Concentration and Hemodilution among Chinese Middle-Aged Obese Men: A Hematocrit-Based Equation for Plasma Volume Estimation Is Induced

Background: A hematocrit (HCT)-based and a body surface area (BSA)-based equations were applied for plasma volume (PV) estimation, respectively, to confirm and quantify the hemodilution effect in prostate-specific antigen (PSA) screening among obese men. The agreement between the equations was additionally investigated. Methods: A total of 1,444 men were retrospectively collected, with ages 40 to 65 years, PSA 0 to 4 ng/mL, and no prostate cancer. PSA mass was calculated as PSA concentration multiplied by PV. Multivariable linear regression models, theoretical models, and the Bland-Altman method were used. Results: PSA concentration significantly decreased with increasing body mass index (BMI; beta = -0.011, P < 0.001); however, PSA mass estimated by HCT-(beta = 0.004, P = 0.132) and BSA (beta = -0.003, P = 0.094)-based equations remained consistent. A screening PSA of 4.0 ng/mL in nonobese men was found to be corresponding to 3.32 and 3.68 ng/mL in obese men extrapolated by PV on the basis of HCT and BSA, respectively. Moreover, the mean (95% confidence interval) difference of PV between the two equations was 0.33 (-0.06 to 0.73) L. Conclusions: The inverse relationship between PSA concentration and BMI might be explained by a hemodilution effect among obese men. There is significant variation in PV calculated by the two equations. Impact: A value between 3.32 and 3.68 ng/mL might be recommended for PSA screening in middle-aged obese Asian men. Cancer Epidemiol Biomarkers Prev;21(10);1731-4. (c) 2012 AACR.