Since you're not getting any better answers as of today....

I don't know a great deal about it, and I'm no doc....and...I don't think it's definitive but I believe low free PSA can be considered a marker for Pca. I also see in searching that 6 % is considered fairly low and may be used in the decision process as an indicator tipping the scale toward a biopsy.

The PSA range is kind of age dependent, meaning the older you get the higher normal PSA can be, but with a PSA of 8, Cancer.org with suggest something like a 25% chance of cancer, over ten is more like a 50% + chance. Given the lower free PSA, that could push the doc toward a biopsy suggestion.

Age and other health factors, i.e. rate of increase of PSA could, of course, play into this decision as well.

In answer to your direct question, I don't know what else could cause that. In searching around it seems the the correlation is the factor the docs use.

Best of luck and good luck to you and your husband!

They are sending him to a specialist for I believe ultrasound/biopsy on August 15 but I was just wondering if there were other things that could make that psa range that low. I do thank you for your reply!

@lorkem258, here is a good explanation from Harvard Medicine:
- What is the difference between PSA and free PSA? Do I need to have both tests? https://www.health.harvard.edu/blog/what-is-the-difference-between-psa-and-free-psa-20091001114