I just posted about PSA's on another thread. I had a PSA test yesterday at Quest Diagnostics in Mpls. PSA was 5.1 compared to 6.2 in Dec at Mayo. Their report states Quest uses the Who system which is 20% lower than Beckman Coulter system . I asked AI (fwiw) what system Mayo uses and they said the Beckman. I haven't seen this mentioned before and am wondering if either system is more common. It's important to know where your baseline came from.