Hemodilution of prostate-specific antigen levels among obese men.

To the Editor: A recent article by Grubb and colleagues (1) shows that the inverse relationship between prostate-specific antigen (PSA) test results and body mass index (BMI) among men from the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial can be explained by the higher blood volume in the obese, an effect called hemodilution (2). Their finding is consistent with our analyses in the EHE International, Inc. clinical population (3). We suggested new PSA cut points for clinical follow-up for obese and morbidly obese men, but agree with Grubb et al. (1) that using body surface area in conjunction with PSA test results to set clinical cut points has merit (3). We suggest an equation based on hemodilution models to standardize PSA test results for differences in body surface. The equation is an algebraic rearrangement of the formulas used by Grubb et al. (1), and ourselves, standardizing the PSA test results to a man who has the mean height for the U.S. (175.77 cm) and whose weight is equivalent to a BMI of 25 for that height (3). The adjusted PSA value can then be compared with standard thresholds for clinical decision making regarding follow-up.