Minnesota DUI attorney David Valentini on challenging blood, urine and breathalyzer tests. What are the grounds for challenging these test.? David explains that the accuracy of the blood, breath, or urine test is important. The machine is reliable but not infallible due to issues that can arise from its computer nature and the need for a known alcohol solution for testing. The solution comes from the Bureau of Criminal Apprehension and breath volumes must be considered. Physical ability to produce a test can also be a factor.