The development of this test has been in the “news” for some months. Here’s a link to an article from last year talking about this same test. It is generally new, and it does have a lower limit than the existing ultra-sensitive tests, but the practical commercial application is still being viewed with skepticism. As usual with the media/news releases, the headline (while eye-catching) overstates the apparent incremental benefit.
Here’s the bottom line
Today’s most sensitive PSA assays (the DPC Immulite sensitive assay) has an analytical detection limit of about 0.002 ng/mL, functional sensitivity of about 0.005 ng/mL and a clinical useful sensitivity of about 0.01 ng/mL. Medical studies demonstrate how ubiquitous and non-specific PSA really is at concentrations below 0.1 ng/mL.
Those of us familiar with the PSA test know very well what PSA specificity means in the context of before treatments…it means that both cancerous and non-cancerous (BPH, infection, recent DRE, bike riding, etc) factors can release abnormally high levels of PSA into the bloodstream.
After surgery, the PSA test also lacks specificity at levels below 0.1 ng/mL because (again) both cancerous and non-cancerous factors can release PSA into the bloodstream in measureable amounts. In addition to the non-specificity, the inherent, naturally occurring variation in PSA (day-to-day, test-to-test) in the blood is now—with the ultrasensitive PSA tests—greater than the measurement detection limits. Studies have shown that the coefficient of variation (CV) based only on daily variation of PSA is between 10% and 20%. The phrase “PSA Anxiety” has taken on several meanings over time, but the original meeting was for exactly this situation (see this article on “PSA Anxiety—The Downside of Ultra-Sensitive Tests”; click on the link, then scroll down to the yellow box at the bottom).
That being said, and with the recognition of “PSA Anxiety” as a very real factor, there is a place for the ultrasensitive PSA test to be used intelligently in monitoring the post-RP patient. The largest group of patients being operated on today have low pre-surgery PSA and low Gleason scores, and after surgery have no EPE and negative margins. Today, these men are commonly prescribed the “standard” PSA test because they have low likelihood of recurrence.
On the other hand, men with any of the factors listed above (high pre-surgery PSA, or intermediate or high Gleason scores, or EPE or positive margins) are excellent candidates for the existing ultrasensitive PSA test. BUT, given the functional coefficient of variation of the non-specific post-surgery PSA levels, there doesn’t appear to be any additional value to push detection limits lower than currently commercially available.
Maybe there is another clinical use of the newest nanoparticle-based assay that will one day become beneficial outside of the research lab…