PSA Density and How It Is Used
PSA density (PSAD) is the amount of PSA per unit volume of prostate tissue. It is determined by dividing the PSA number by the prostate volume (its size measured by transrectal ultrasound). The idea is that when cancer is not present, the increase in PSA is directly proportional to the volume of the prostate. Therefore, the density of PSA remains about the same. But, with cancer, PSA increases more than would be expected from the size of the prostate. Thus, the density of PSA is higher. A PSAD of 0.15 or more is thought to suggest cancer.
Unfortunately, PSA density has not proved to be a reliable differentiator of BPH and cancer and, thus, has fallen out of favor as an additional screening tool when PSA is in the borderline range. The problem is that it requires ultrasound, which adds to the cost and time involved. But, more importantly, transrectal ultrasound has not been shown to measure the volume of the prostate reliably. And, with the ease of needle biopsy, if transrectal ultrasound is going to be done for a suspicious DRE or PSA, a biopsy is usually done, too.
