Prostate Volume & PSA Density Calculator
Understanding Prostate Volume Calculation
Calculating the volume of the prostate is a critical step in urological health assessments. It helps clinicians differentiate between Benign Prostatic Hyperplasia (BPH) and potential malignant conditions. The most common method used by radiologists during an ultrasound (TRUS) or MRI is the prolate ellipsoid formula.
The Ellipsoid Formula
Since the prostate is roughly shaped like a walnut or a rounded triangle, its volume is estimated using three diameters:
- Width (Transverse): The measurement from side to side.
- Height (Anteroposterior): The measurement from front to back.
- Length (Cephalocaudal): The measurement from the base to the apex.
The standard formula is: Volume = Width × Height × Length × 0.524.
What is PSA Density?
PSA Density (PSAD) is a calculation that relates the level of Prostate-Specific Antigen in the blood to the size of the gland. Larger prostates naturally produce more PSA. A high PSA in a small prostate is more concerning than the same PSA level in a very large prostate. Generally, a PSA density of 0.15 ng/mL/cc or higher may indicate a need for further investigation, such as a biopsy.
Normal Prostate Volume Ranges
A typical young adult's prostate volume is approximately 20-25 mL (or cubic centimeters). As men age, the prostate often grows due to BPH. Volumes over 30-40 mL are generally considered enlarged. In extreme cases of BPH, volumes can exceed 100 mL.
Clinical Example
If a patient has a prostate with a width of 4.0 cm, a height of 3.0 cm, and a length of 3.5 cm, the calculation would be:
4.0 × 3.0 × 3.5 × 0.524 = 22.0 mL
If that same patient has a total PSA of 3.3 ng/mL, their PSA density would be 3.3 / 22.0 = 0.15 ng/mL/cc.