PSA density

PSA density is the serum prostate-specific antigen in nanograms per millilitre divided by the prostate volume in millilitres, taken from the multiparametric MRI. It exists because benign prostatic enlargement raises PSA on its own: a 100 mL gland with a PSA of 8 is behaving differently from a 30 mL gland with the same figure. It is used at two points. In the NCCN very low risk definition a density below 0.15 is one of the criteria, alongside clinical stage T1c, grade group 1, PSA under 10 and fewer than three positive cores with no more than half of any core involved. And it is used in deciding whether a man with a negative or equivocal MRI needs a biopsy at all, where a low density supports omitting one and a high density argues for going ahead.

NICE NG131 does not set a density threshold. It offers multiparametric MRI first, reported on a five-point Likert scale, offers MRI-influenced biopsy at Likert 3 or above, and allows omitting biopsy at Likert 1 or 2 after a shared discussion of the risks and benefits, with systematic biopsy offered to anyone who still wants one; density is one of the things clinicians weigh in that discussion rather than a rule in the guideline. Density is also one of the inputs that gives the NCCN and Cambridge systems different very-low-risk populations, since the Cambridge groups do not use it.