Hi, welcome. It's my understanding that interstitial cystitis is not usually associated with blood in the urine. Interesting that gross hematuria stopped so soon after starting antibiotics. That certainly would leave one to think the cause of the blood is due to a UTI. So, when I have had a UTI, they check for bacteria in the urine sample in the office and then let the culture sit and then check it again a day later. That is often when I've then been diagnosed with a UTI. Your urinalysis was normal, but will they recheck it?
What are they going to biopsy? The areas of inflammation or the area of erythematous mucosa (which means read areas I believe)? Blood in urine is most commonly caused by stones or UTI. I think they are being very cautious. They say pretty clearly no tumors. However, they want to check which hey, that's good. Better safe than sorry. Here is information on bladder cancer. https://www.mayoclinic.org/diseases-conditions/bladder-cancer/symptoms-causes/syc-20356104 Blood in urine can be a sign of that but let's not forget it got better with Cipro. It's hard with you to determine if there is an infection due to the chronic nature of your symptoms of interstitial cystitis. Ugh. When is your appointment?