A prospective evaluation of the effect of finasteride on prostate health index ( phi )

Purpose 5-alpha reductase inhibitor (5ARI) reduces prostate-specific antigen (PSA) by half but its effect on prostate health index ( phi ) is unknown. This study aims to investigate this effect and to enable accurate interpretation of phi in men with elevated PSA and on 5ARI. Methods This is a prospective study evaluating the effect of finasteride on PSA, free PSA (fPSA), [ – 2]proPSA (p2PSA) and phi at 6 and 12 moths in men with PSA 4-20 ng/mL, no prior 5ARI use, and one negative prostate biopsy within 6 months before recruitment. The 5ARI Finasteride (5 mg/day) for 1 year was offered if International Prostatic Symptom Score (IPSS) was ≥ 8 at baseline. 5ARI group included patients taking finasteride, while control group included patients not on finasteride. The blood results were compared with t -test between baseline and different time points in each group and between groups at 1 year. Results 164 men fit the inclusion criteria and 150 were analyzed. In 5ARI group (n = 100) at 1 year, mean PSA reduced by 51.4% from 8.9(± SD 3.7) to 4.4(± SD 2.8)ng/mL (paired t-test, p < 0.001), fPSA reduced by 52.4% from 1.6(± 0.6) to 0.8(± 0.4)ng/mL (p < 0.001), p2PSA reduced by 55.3% from 18.4(± 8.8) to 8.3(± 5.6)pg/mL (p < 0.001), and phi reduced by 34.2% from 33.7(± 11.9) to 22.4(± 12.5) (p < 0.001). PSA and phi values in the control group remained static over 1 year and significantly higher than those in 5ARI group. Conclusion This study demonstrated p2PSA and phi are reduced by about 55% and 34% in men on 5ARI. A conversion factor of division by 0.66 is needed for phi in men on finasteride to allow the interpretation and use of phi in men on 5ARI.