Hemodilution of PSA in obese men could delay diagnosis of prostate cancer

Bañez LL et al. (2007) Obesity-related plasma hemodilution and PSA concentration among men with prostate cancer. JAMA 298: 2275–2280

Elevated serum levels of PSA provide a good primary indicator of prostate cancer and are often used to prompt diagnostic biopsy. A recent report from Bañez et al. suggests that the increased plasma volume of obese men dilutes their PSA concentration, and gives a falsely low level that could delay cancer diagnosis.

This multicenter study assessed associations between preoperative BMI and serum PSA concentration in three cohorts of patients, totaling almost 14,000 men, who all underwent radical prostatectomy between 1988 and 2006. Blood plasma volume was estimated as a function of height and weight; consequently, high BMI was strongly associated with increased plasma volume in all cohorts. Obese men (BMI >35 kg/m²) were found to have 11–21% lower PSA concentrations than nonobese men (BMI <25 kg/m²); however, obese men in all three cohorts had circulating PSA masses (calculated by multiplying serum PSA concentration by estimated plasma volume) similar to or even higher than those of nonobese men, which suggests that hemodilution accounts for the low serum PSA values of obese men.

These findings might help to explain epidemiological observations that obesity is associated with poor outcomes and increased mortality among men with newly diagnosed prostate cancer. The authors conclude that further prospective studies in screened populations that include men without prostate cancer will be required to confirm the extent to which hemodilution influences the low PSA values of obese men.