PSA doubling time as a screening test to predict bone scan positivity

Aims: The aim of this article is to compare the effectiveness of PSADT and tPSA as predictors of bony metastases in patients’ with prostate cancer pre-definitive treatment, and help guide clinicians with the selective ordering of bone scans (BS). Materials and methods: PSA measurements were retrospectively analysed for 330 men with prostate cancer, investigated with BS between 2009 and 2012. Exclusion criteria included previous positive BS, other malignancy, prostatectomy/radiotherapy and any prostate-specific condition or treatment initiated between the PSA levels used to calculate doubling time. PSADT (months) = log2 × dT/(log(PSA₁)–log(PSA₂)). Results: A total of 273 men had negative BS and 57 had positive findings of metastases. Those with positive BS had significantly (p < 0.05) faster median PSADT (4.5 vs 15.2 months) and higher median tPSA (94 vs 24.5 ng/ml). On ROC curve analysis, PSADT outperformed tPSA as a predictor of bone scan result, with area-under-the-curve of 0.85 vs 0.76 (p = 0.02). A ratio (R) of tPSA/PSADT was no better than PSADT alone (p = 0.65). Conclusions: In the absence of clinical reasons to suspect metastatic disease, it is appropriate to withhold ordering a BS for non-prostatectomy/radiotherapy patients with rising PSA levels, until the PSADT is less than 18 months. This has a sensitivity of 100.0% and a specificity of 41.0%.