If UK , Professor James - Malone Lee.
By looking at a fresh sample of urine ( as in immediate ) under a microscope, looking for epiffeal ( sp) and pud cells.
He does not believe in IC , it is imbedded infection " buried into the bladder wall " there are quite a few specialists who " quietly" believe this is the case also , but womtnput there heads on the parapet as it would change so much surrounding treatment on chronic UTIs.
However oestrogen is " mother natures " antibiotic , so leaves us far more susceptible to chronic infections , so I would start at getting back on systemic and local HRT asap.