Prostate Health Index
Prostate-specific antigen (PSA) is a glycoprotein produced by the prostate gland. Measurement of serum PSA is useful for determining the extent of prostate cancer and assessing the response to prostate cancer treatment. PSA is also used as a screening tool for prostate cancer detection. While an elevated serum PSA is associated with prostate cancer, a number of benign conditions, such as benign prostatic hyperplasia (BPH) and prostatitis might lead to elevated serum PSA concentrations. PSA lacks specificity for prostate cancer detection.
Several PSA isoforms have been identified that can further increase the specificity of PSA for prostate cancer. In particular, the [-2] form of proPSA (p2PSA) shows improved performance over either total or free PSA for prostate cancer detection on biopsy. The prostate health index (phi) is a formula that combines all 3 PSA forms (total PSA, free PSA, and p2PSA) into a single score. Phi is calculated using the following formula: (p2PSA/free PSA) x square root (PSA).
Prostate health index (phi) may be used to determine the probability of prostate cancer on biopsy in men with total PSA in the 4 to 10 ng/mL range. Low phi scores are associated with a lower probability of finding prostate cancer on biopsy and higher phi scores are associated with an increased probability of finding prostate cancer on biopsy. The choice of an appropriate phi score to be used in guiding clinical decision-making may vary for each patient and may depend on other clinically factors or on family history of disease.
| Phi Range | Cancer Probability | 95% Confidence |
| 0-26.9 | 9.8% | 5.2-15.4% |
| 27.0-35.9 | 16.8% | 11.3-22.2% |
| 36.0-54.9 | 33.3% | 26.8-39.9% |
| 55.0 or greater | 50.1% | 39.8-61.0% |
Protate health index is calculated when total PSA is in the range of 4 to10 ng/mLProstate health index is not calculated when the total PSA is <4 or >10 ng/mL. The percent of free PSA is only calculated when total PSA is between 4 and 10 ng/mL.
Specimens for [-2]ProPSA (p2PSA) testing should be drawn prior to prostate manipulations such as digital rectal examination (DRE), prostatic massage, transrectal ultrasound (TRUS), and prostatic biopsy. DRE may cause a transient increase in p2PSA, free PSA, and PSA. Specimen requirement is a red top tube of blood.
Phi is an FDA approved immunoenzymatic assay manufactured by Beckman Coulter and performed on a Beckman Coulter immunoassay analyzer.
References
Loeb S, Sanda MG, Broyles DL, et al. The prostate health index selectively identifies clinically significant prostate cancer. J Urol. 2015;193(4):1163-9.
Catalona WJ, Partin AW, Sanda MG, et al: A multicenter study of [-2]pro-prostate-specific antigen combined with prostate-specific antigen and free prostate-specific antigen for prostate cancer detection in the 2.0 to 10.0 ng/mL prostate-specific antigen range. J Urol 2011 May;185:1650-1655
2. Pecoraro V, Roli L, Plebani M, el al: Clinical utility of the (-2)proPSA and evaluation of the evidence: a systematic review. Clin Chem Lab Med 2015 Nov 26. pii available at /j/cclm.ahead-of-print/cclm-2015-0876/cclm-2015-0876.xml. doi: 10.1515/cclm-2015-0876
3. Loeb S, Catalona WJ: The Prostate Health Index: a new test for the detection of prostate cancer. Ther Adv Urol 2014 Apr;6(2):74-77 doi: 10.1177/1756287213513488
