Prostate Volume & PSA Density
Calculates ellipsoid prostate volume and PSA density to refine cancer suspicion.
Prostate volume is estimated with the ellipsoid formula (L × W × H × π/6 ≈ 0.52). Dividing serum PSA by this volume gives PSA density, which improves the specificity of PSA for clinically significant cancer, particularly in men with an enlarged gland.
📐 Formula
Volume = L × W × H × 0.52 mL; PSA density = PSA / volume
🎯 When to Use
- MRI or transrectal ultrasound sizing of the prostate.
- Risk-stratifying an elevated PSA before biopsy.
- Reporting PSA density alongside PI-RADS assessment.
⚙️ How It Works
- Measure the three maximal orthogonal prostate dimensions in cm.
- Volume = length × width × height × 0.52 (millilitres, approximately equal to grams).
- PSA density = serum PSA ÷ prostate volume.
- Interpret the density against the 0.15 ng/mL/mL threshold.
📊 Interpreting the Result
- PSA density > 0.15 ng/mL/mL raises suspicion for clinically significant prostate cancer.
- Higher density strengthens the indication for biopsy, especially with a suspicious MRI lesion.
- Density ≤ 0.15 in the setting of a benign-appearing enlarged gland supports a benign cause of the raised PSA.
⚠️ Limitations & Pitfalls
- The ellipsoid formula assumes a regular shape and can misestimate irregular or asymmetric glands.
- PSA can be elevated by prostatitis, instrumentation or recent ejaculation independent of cancer.
- The 0.15 threshold is a guide, not a hard rule; use it with MRI and clinical context.
📚 References
- Nordström T, Akre O, Aly M, et al. Prostate-specific antigen (PSA) density in the diagnostic algorithm of prostate cancer. Prostate Cancer Prostatic Dis. 2018;21(1):57-63.
- Terris MK, Stamey TA. Determination of prostate volume by transrectal ultrasound. J Urol. 1991;145(5):984-987.
⚕️ For clinical decision support only. Always verify calculations and apply clinical judgment.