PSA Density Calculator
PSA Density Calculator
Correct total PSA for prostate size to separate benign enlargement from a result that warrants biopsy.
PSA Density
PSA ÷ volumeTotal PSA 6.2 ng/mL, prostate volume 48 mL
Formula
- PSA
- total serum PSA, ng/mL
- volume
- prostate volume in mL, usually measured on transrectal ultrasound or MRI using the ellipsoid formula (length × width × height × 0.52)
Worked example
Total PSA 6.2 ng/mL, prostate volume 48 mL
6.2 ÷ 48 = 0.129 ng/mL/mL
This sits in the intermediate band, between the 0.10 and 0.15 thresholds
PSA density thresholds
| Density | Typical interpretation |
|---|---|
| Below 0.10 | Reassuring — favours benign enlargement |
| 0.10 – 0.15 | Intermediate — correlate with MRI and kinetics |
| Above 0.15 | Traditionally favours biopsy |
Correcting PSA for gland size
PSA density corrects the total PSA for the size of the gland that produced it, because benign prostatic hyperplasia raises PSA simply by adding secretory tissue — a large benign gland and a small malignant one can generate the same total PSA. Dividing by volume removes most of that size effect and leaves a number that tracks glandular activity per millilitre rather than gland bulk.
A density below 0.10 ng/mL/mL is reassuring and is widely used in active surveillance protocols to support continued monitoring rather than intervention, and in deciding against biopsy when an MRI is equivocal at PI-RADS 3. Above 0.15 has traditionally been the threshold favouring biopsy, though most contemporary pathways now weigh it alongside MRI findings rather than acting on density alone.
The main limitation is that volume is itself an imperfect measurement. It is usually taken from transrectal ultrasound or MRI using the ellipsoid formula — length × width × height × 0.52 — and inter-observer variability in that estimate propagates directly into the density calculated from it. A volume that differs by 20% between two readers moves the density band without any change in the patient.
Frequently asked questions
What is a normal PSA density?
Below 0.10 ng/mL/mL is generally reassuring. Above 0.15 has traditionally been the threshold favouring biopsy, with 0.10–0.15 treated as an intermediate zone requiring further correlation.
Why does PSA density matter if total PSA is already raised?
A large benign gland can raise total PSA to the same level as a small malignant one. Dividing by volume separates the two by asking how much PSA each millilitre of gland is producing.
How is prostate volume measured?
Usually by transrectal ultrasound or MRI, applying the ellipsoid formula: length × width × height × 0.52. It is an estimate, and different readers can disagree by 20% or more.
Can PSA density be used instead of biopsy?
No. It is a triage tool that helps decide whether biopsy is warranted, particularly alongside MRI, not a substitute for histological diagnosis.
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References
- Benson MC et al. Prostate specific antigen density: a means of distinguishing benign prostatic hypertrophy and prostate cancer. J Urol. 1992;147(3 Pt 2):815–16.
- Nordström T et al. Prostate-specific antigen (PSA) density in the diagnosis of prostate cancer. BJU Int. 2018;122(4):604–11.