The illusion of prostate-specific antigen decline in patients with metabolic syndrome and insulin resistance

OBJECTIVE To investigate the detailed mechanism of prostate-specific antigen (PSA) decline in metabolic syndrome (MS) and insulin resistance (IR), which lowers the predictive value of the PSA test, we examined the effect of haemodilution and the possibility of an intrinsic metabolic effect. PATIENTS AND METHODS We analysed 28 315 men who underwent routine check-ups. We compared the age-adjusted mean PSA levels in subjects with and without MS before and after adjusting or stratifying the plasma volume. We analysed changes in PSA level, plasma volume and PSA mass according to obesity grade, number of MS components, IR severity and diagnosis of MS, IR or both using an analysis of covariance. RESULTS The PSA levels were lower in the group with MS than in the group without MS (P = 0.001), but this difference disappeared after adjusting or stratifying the plasma volume (P > 0.05 for all). The PSA levels decreased, plasma volume increased, and PSA mass did not change as the number of MS components increased (P = 0.002, P < 0.001, P = 0.55, respectively) or the IR severity increased (P = 0.001, P < 0.001, P = 0.34, respectively). Similarly, PSA levels were lower, plasma volumes were higher and PSA masses were the same in subjects with MS (P = 0.002, P < 0.001, P = 0.10, respectively), IR (P = 0.018, P < 0.001, P = 0.94, respectively), or both (P = 0.003, P < 0.001, P = 0.86, respectively) than in subjects without those conditions. CONCLUSION The PSA decline in MS and IR may result simply from a haemodilution effect and be unrelated to intrinsic metabolic disturbances. For this reason, PSA levels could be underestimated in patients with MS or IR because of haemodilution.