Urinating problems

Patient: My husband randomly has to take a DOT drug test every so often for his job. He states that he urinates only a couple times a day. He says that when he has to go for the test that he can’t give a sample because he can’t urinate. He is given a 3 hr window to give a sample, they give him fluids to drink during that time, but he says he still is unable to go. My question is this, should a person be able to at least go a little bit after drinking for 3 hrs.? He was fired from his job for refusing to give a urine sample.

Doctor: