A recent journal article in BJUI  provides an interesting perspective on the interplay between obesity and the accuracy of PSA for predicting prostate cancer. Research has shown an inverse relationship between body mass index (BMI) and serum PSA levels . Two explanations for this relationship have been recently proposed. One is the anti-androgen theory. In this hypothesis, it is speculated that the lower androgen levels in obese men (probably due to increased aromatisation to oestrogen in adipocytes leading to feedback inhibition in the pituitary) leads to decreased androgen stimulation of the prostate gland and less PSA production (PSA is an androgen-regulated gene) . On the other hand, the haemodilution theory suggests that obese men have lower PSA levels due to larger circulating plasma volumes that dilutes the PSA, as PSA is measured by concentration (i.e. amount per volume) .
This paper by Oh et al.  has several notable findings, the first of which is that BMI does have an inverse relationship with PSA, consistent with prior studies . Secondly, a higher BMI was significantly associated with an increased risk of prostate cancer detection when controlled for potentially confounding variables, e.g. age, PSA level, DRE findings, and prostate volume. Additionally, the accuracy of PSA in predicting prostate cancer did not change regardless of BMI category. This last point is central to the main question of the paper – should there be a lower PSA threshold for obese man based on BMI?
Certainly if the haemodilution theory holds true, which multiple studies have suggested  obese men would probably have prostate cancer at a lower PSA level when compared with non-obese men, all else equal. This paper suggests that among all BMI groups, accuracy of PSA in predicting prostate cancer did not significantly change. The importance of this issue rests on the fact that obese men have been shown in prior studies to have prostate cancer-related death at a much high rate than non-obese men , while also having a lower serum PSA. The detection bias has paramount clinical significance as it can result in a delay in diagnosis and ultimately treatment, potentially leading to adverse outcomes.
The implications from this study  are that PSA can still be used as a screening tool for prostate cancer in obese men. Moreover, this paper argues that the threshold values used in obese men should be lower. While there is no universally accepted threshold value among the urology community to distinguish between benign prostate disease and prostate cancer, threshold values are often used by individual urologists. As such, for whatever threshold value one feels is best, it should be lower in men with higher BMI: ≈7% lower in overweight men, 14% lower in obese men, and 18% (or more) in very obese men . Only through this approach, can we attempt to level the playing field for obese men.