PHI Is Blood Serum Immunoassay
In contrast, the PHI is an in vitro diagnostic multivariate index assay that combines three blood serum PSA immunoassays — PSA, free PSA, and p2PSA — into a single calculation (p2PSA/free PSA) × √total PSA.
The test is simple and inexpensive and has performed better than conventional PSA and free PSA measures in several studies for predicting overall and high-grade prostate cancer.
For the current draft NICE guidance, researchers from the External Assessment Group conducted three systematic reviews of the evidence, identifying 6 studies that reported the analytical validity and 31 that reported the clinical validity of the tests. No studies that reported the clinical validity of the tests were identified.
In addition, the group conducted a systematic review of the existing economic analyses of the PCA3 and PHI tests. Because no published economic studies met the inclusion criteria, the group designed their own de novo economic model designed to assess the cost-effectiveness of the tests.
After reviewing the available evidence, the guidance committee considered whether more research into the two assays was advisable.
Noting that any potential improvements to the tests would be small, the guidance says: "If the potential benefits of using the PCA3 assay and the PHI were realised, they were unlikely to be sufficiently large to offset the costs of the test and make a substantial difference to the number of people having a second biopsy unnecessarily."