Comparison of digital examination and transrectal ultrasonography for the diagnosis of prostatic cancer.

The ability to detect prostatic cancer by transrectal ultrasonography was evaluated in a prospective blind study of 216 men. The sensitivity of transrectal ultrasonography was 86 per cent but the specificity was only 41 per cent. Tumors less than 1 cm. in diameter were most difficult to detect by transrectal ultrasonography. The positive and negative predictive values of transrectal ultrasonography were 36 and 89 per cent, respectively. Abnormal scans that strongly suggested carcinoma were present in 10 per cent of the men who had a normal digital examination but no biopsy was performed. Transrectal ultrasound is a sensitive method to detect all but small prostatic tumors and it can detect tumors that are not evident by digital examination. To date, however, transrectal ultrasonography may be difficult to use for routine screening in the United States because of the low positive predictive value. Nevertheless, further investigation of this technique is warranted to define its role in improving the diagnosis of prostatic cancer.