In general, any PSA result that can give a lower number than 0.1 is "ultra-sensitive", at least that's my understanding. I had originally requested the "standard" test from my local urologist because a) I had a good pathology report, and b) I thought I would fret over possibly more "noise" in the movements of PSA results over time. However, what I received the ultra-sensitive type.
The question is a bit more complicated as there have been several generations of lab equipment and assays. I don't have a link to post, but a quick search on "PSA ultra sensitive" should bring up a lot on the subject. There is more than one generation of equipment of the ultra-sensitive variety, and variations between equipment manufacturers as well. I found it useful to actually look up the specs of the equipment used on my PSA result, which was right there on the report. I also learned that there is a lot of variance in the results when the reported PSA level is near the lowest level of sensitivity for that particular equipment/assay, hence the importance of knowing which machine was used. There is a term "functional sensitivity" which is the level that test results are repeatable for a given test, and this level is higher than then the lowest sensitivity specified. For example, a test that has a sensitivity of "<0.008ng/ml" may yield a result of 0.009 for a particular man, but that number may vary greatly over multiple tests. On the other hand, a result of 0.015 may be very reproducible. This is just an example.
Age:45 (44 when diagnosed)
Father diagnosed and cured at age 52.
08/21/07: Diagnosed with T1c cancer
1 of 12 biopsy cores positive; 10% tissue
Gleason score: 3+3=6
PSA level prior to biopsy: 4.3 (velocity < 0.4ng/ml)
10/19/07: da Vinci prostatectomy by Dr. Vipul Patel
Difficult surgery due to prostate inflammation.
Both nerve bundles spared.
Spongy erections began within 24hrs of surgery!
10/24/07: Catheter out; down to 1 Serenity pad/day next day.
Final pathology: neg margins, no capsular penetration,
Gleason 3+3=6, 5% tumor involvement, multi-focal.
11/04/07 First usable erection with Cialis
11/22/07 Thanksgiving - Bye-bye, pads
01/17/08 First post-surgery PSA result: < 0.008 ng/ml