Interexaminer reliability and validity of a three-dimensional model to assess prostate volume by digital rectal examination

Objectives. To evaluate the interexaminer reliability and accuracy compared with transrectal ultrasound (TRUS) of a three-dimensional (3D) model and other scales to improve the estimation of prostate volume by digital rectal examination (DRE). Methods. Volunteers from a urology clinic (n = 121) were examined independently by three examiners with different levels of experience in randomized order. During DRE, the examiners estimated the prostate size in increments of 5 g, using various rating scales and a 3D sizing model, without access to the findings of the other investigators. TRUS was then performed by each examiner. Results. The 121 volunteers were 39 to 82 years old, with a mean ± SD total TRUS prostate size of 35.9 ± 27.2 g. The DRE size estimates ranged from 15 to 100 g across all examiners and patients. The interexaminer reliability across examiners for the best DRE prostate size estimates (in grams) was 0.78 (95% confidence interval 0.70 to 0.84), and the correlation coefficients (r_s) with the TRUS volume ranged from 0.61 to 0.72 for the three examiners. A 3D model showed good reliability (intraclass correlation coefficient 0.86, 95% confidence interval 0.75 to 0.93), and correlated well with the TRUS volume (r_s = 0.67 to 0.75). Other scales showed fair reliability (0.58 to 0.68) and correlated with the TRUS measurements (0.57 to 0.67). The area under the receiver operating characteristic curve to identify prostate volumes greater than 40 g ranged from 0.78 to 0.90 for DRE estimates (in grams) and 0.69 to 0.89 for the 3D model. Conclusions. DRE size estimates and TRUS volume were moderately to highly correlated in men without prostate cancer. A 3D sizing model showed comparable reliability and correlation with TRUS. Although the DRE estimates generally tend to underestimate the TRUS-measured prostate volume, these tools may be useful in identifying men with enlarged prostate glands.