What could cause bubbles in urine?

Protein: Bubbles in the urine or "foamy" urine is always worrisome for the possibility of protein in the urine. If this occurs, the doctor can check a urinalysis for the presence of protein. If this is positive, further tests can be done to determine the amount of protein that is being leaked into the urine and what the cause of the protein in the urine is.

Protein in urine: Protein in the urine will be displayed as "foamy" urine. This is concerning and should be assessed by your doctor. Air in the urine or Pneumaturia, defined as the passage of “gas” in the urine, is the result of gas in the urinary tract and can be due to recent instrumentation, fistulae into the bladder or upper urinary tract from the bowel or vaginal canal.