DWI Fundamentals: Breath vs. Blood Which test is more accurate & why? DWI Fundamentals: Breath vs. Blood. In any Driving While Intoxicated (DWI) investigation, determining an individual’s level of intoxication is essential. Obtining accurate measurements of someone’s Blood Alcohol Content (BAC) are crucial. In addition to accurate measurements, reliability of alcohol testing methods can make all the difference. If the equipment cannot produce a reliable result, it is not useful evidence. Blood tests and breath tests measure Blood Alcohol Content (BAC). While both methods serve the same purpose, there’s a prevailing belief that blood tests are inherently more accurate than…