Ed,
Your result is 0.008, which is double 0.004, but you're in the trillionth of a gram weight territory here, which is not a meaningful increase. Ultra sensitive PSA testing can cause unneeded anxiety, especially when you see numbers increasing like this. Your latest result would need to multiply by 25 before you reach the AUA standard (0.2) for beginning any kind of further treatment.
You're undetectable, negative, zero, etc. Make mine a cuppa!
Take care and hang in there...Tim