That’s a great response from Nobody and here are my immediate thoughts.
I can see from your first message (Guidance on febuxostat, colchicine, and NSAIDs) that your husband’s uric acid levels have been 250-300 since around December 2017. Unusually, your rheumatologist’s advice at that time was to aggressively increase febuxostat dose to 120mg. So that resulted in uric acid of 149 μmol/L in January this year.
Personally, I’m a fan of such an aggressive approach to reduce the time for uric acid debulking. But that has to be something that is agreed by doctor and patient. Because a thorough risk assessment of high-dose uric acid treatment is important. Also, we’re all concerned about the long-term effects of febuxostat compared to allopurinol. So, it is important to leave the consultation with enough information for you and your husband to be happy that he is getting the right uric acid treatment at the right dose.
With respect to GFR, I’ve learned that it tends to decrease with age and with gout. But studies indicate that both allopurinol and febuxostat tend to raise GFR. So I’d ask your new rheumatologist if she/he knows of any evidence to show which is best. I’m aware that other factors influence GFR so there might not be a definitive answer.
Unfortunately, none of us can assess the length of time it takes for all old crystals to dissolve. So, as Nobody says, “it’s too early to rule out residual gout as the cause of some of your husband’s symptoms”. However, there is a faint hope that your new rheumy knows where you can get access to a DECT scan for gout management. If so, please tell! Because that’s the Holy Grail for assessing how uric acid treatment is really progressing.