If a Houston traffic stop turns into a DWI investigation and ends with a blood draw, it can feel like the outcome is already decided. Prosecutors present blood results as the definitive answer — a machine produced a number above 0.08, and that is that. It is more complicated than that, and the reasons are worth understanding. A blood result depends on the constitutional basis for taking the sample, the procedure used to draw it, how it was stored, and how it was analyzed. Wea