I Have Been On Methylphenidate 10 Mg For Years. I

I have been on methylphenidate 10 mg for years. I also have diabetes and therefore frequently go to bathroom. This morning I took my meds at 8:00 and saw my neurologist at 2. From 8 to 2 I went to bathroom at least 10 times. When I submitted a urine sample it did not show any of my methylphenidate in my system. Is this medicine metabolized that fast? The doctor acted like there was something wrong and required another urine test. What do you think?