"Didn't make full use of evidence from test"

My consultant referred me for an

XRay barium enema to help diagnose a possible fistula. When the appointment came it was for a CTVirtual colonoscopy. I was told that the radiology department have stopped offering XRay barium enemas. I was told the CT was a better test anyway so I went ahead with it. The day before the test I had to drink a solution of barium. A few hours afterwards I notice white granules in my urine. I assumed this was the barium and kept a urine sample as I thought it would be helpful for the doctors who were looking for evidence of a fistula. I asked the hospital if they wanted to test the sample to confirm if it was the barium in my urine and they said they didn't. The consultant has written to me and said the CTVirtual colonoscopy has shown no evidence of a fistula. Why isn't the barium in the urine used as evidence to help diagnose and speed up my treatment?