Should the digital rectal examination still be used to screen for prostate cancer?

There is little evidence to support the use of digital rectal examination (DRE) as a screening for prostate cancer, according to a review and meta-analysis published in the Annals of Family Medicine.

Although the DRE is often performed routinely in men to screen for prostate cancer, some evidence suggests that it may result in a high number of false-positives. This could lead to unnecessary diagnostic tests, as well as over-diagnosis and over-treatment of prostate cancer.

Leen Naji, MD, from the Department of Family Medicine at McMaster University in Hamilton, Ontario, Canada, and colleagues, conducted an extensive search of the medical literature to evaluate the diagnostic accuracy of DRE in screening for prostate cancer in the primary care setting.

The search strategy was developed by an experienced health sciences research librarian and included the key concepts of prostate cancer, DRE, and biopsy. Digital rectal exam was performed by a primary care clinician, and a biopsy determined the diagnosis. All studies reported true-positive, true-negative, false-positive, and false-negative rates of DRE, or provided at least two of these values to allow for the calculation of at least one of four measures: sensitivity, specificity, positive predictive value (PPV), or negative predictive value (NPV).

Studies were evaluated independently by three pairs of reviewers to determine whether they met the eligibility criteria.

The study quality was assessed with the Quality Assessment of Diagnostic Accuracy Studies 2 (QUADAS-2) tool. The Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) framework evaluated the quality of evidence of pooled analyses across 5 domains: risk of bias, indirectness, inconsistency, imprecision, and publication bias.

A meta-analysis determined the sensitivity, specificity, PPV, and NPV values obtained from the individual studies.

From 8,217 studies identified, seven studies with 9,241 patients who underwent both DRE and prostate biopsy and met other screening criteria were selected.

According to the QUADAS-2 criteria, all seven studies had possible risk of bias because participant enrollment methods lacked clarity in most studies. In addition, not all studies explicitly stated their criteria for an abnormal DRE, and only patients with an abnormal PSA or DRE underwent the prostate biopsy.

The overall quality of the evidence in the studies was very low according to the GRADE assessment; reasons for the poor rating were primarily due to risk of bias, inconsistency, and imprecision. In addition, small sample size and heterogeneity of some studies limited the value in determining publication bias.

In pooled analysis of the 7 studies, DRE performed by primary care clinicians generally had poor performance for prostate cancer screening, and there was high heterogeneity across studies. Of the DRE performed by primary care clinicians, pooled sensitivity and specificity was 0.51 and 0.59, respectively. Pooled PPV and NPV was 0.41 and 0.64, respectively.

The authors explained that between-study heterogeneity in the meta-analyses may have resulted from the various definitions used for abnormal DRE or from differences in training for primary care practitioners. A survey across Canadian medical schools revealed considerable differences in teaching methods for DRE. Approximately one-half of graduating students had never performed a DRE during their clerkship training, and only one-half of surveyed primary care physicians reported feeling confident in their ability to detect prostate nodules using DRE.

The authors acknowledge that the review has several limitations. Many studies did not report the setting in which, or by whom, the DRE was performed. In addition, there was substantial variation in both setting and reported diagnostic accuracy of DRE, and only patients with a positive DRE or elevated PSA level underwent a biopsy, which has the potential for underestimating the false-negative rate. The sensitivity and NPV of DRE were also overestimated.

The investigators feel that the DRE does not meet the World Health Organization stipulation that screening tests must have scientific evidence to demonstrate effectiveness, and the benefits of screening should outweigh harms.

Although they did not evaluate the possible risks of DRE, they concluded that “Given the considerable lack of evidence supporting its efficacy, we recommend against routine performance of DRE to screen for prostate cancer in the primary care setting.”

To read more about this study, click here.