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Genitourinary
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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.

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📐 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.