Determination of optimum cutoff value of serum prostate-specific antigen in prediction of skeletal metastases on technetium-99m whole- body bone scan by receiver operating characteristic curve analysis

Elevated serum prostate-specific antigen (Sr.PSA) levels have high predictive value for skeletal metastases; however, there is no consensus regarding cut-off value of Sr.PSA above which bone scan is indicated. This study was performed to find out the accuracy of Sr. PSA test in prediction of skeletal metastases on bone scan and to find optimum cutoff value of Sr.PSA to exclude the bone scan in staging of prostate cancer. Retrospective analysis of medical records of 305 prostate cancer patients referred to nuclear medicine for bone scan between June 2012 and June 2015 was done. Out of 305 patients, 13 cases were excluded due to nonavailability of Sr.PSA. Technetium-99m methylene diphosphonate bone scan was performed with standard protocol. Out of 292 cases, 174 patients (59.58%) had positive bone scan for metastases and 118 (40.41%) patients had negative scan for metastases. 44 (15.06%) patients had super scan. On comparison of mean Sr.PSA levels between positive and negative groups, we found significant Sr.PSA levels (P < 0.001). We used receiver operating characteristic (ROC) curve to find out accuracy of Sr.PSA test in prediction of skeletal metastases on bone scan and to know optimum cutoff value of Sr.PSA to avoid the unnecessary bone scans. Area under ROC curve was 0.878 (87%). This indicates the accuracy of Sr.PSA test in prediction of skeletal metastases on bone scan was good. Optimum cutoff value of Sr.PSA to avoid the bone scan in staging of prostate cancer was <29.1 ng/ml with sensitivity and specificity of 89.0% and 74.6%, respectively. With this study, we conclude accuracy of Sr.PSA test in prediction of skeletal metastases is good. Optimum derived cutoff value of Sr.PSA for positive skeletal metastases is >29 ng/ml and that bone scan may be excluded in patients who have Sr.PSA >29 ng/ml. (author)