How accurate and reliable are the police methods used to determine alcohol concentration?

Texas law provides that testing of alcohol concentrations can be performed by analysis of a DWI suspect's urine, blood or breath. All three of these testing methods, however, leave much to be desired.

Urine testing is the least accurate and least reliable means of alcohol concentration testing. Indeed, there appears to be no debate in the scientific community that this method of alcohol concentration testing is the least preferred.

Blood testing, unlike that of urine testing, is thought by the majority of forensic scientists to be the most accurate and reliable means of alcohol concentration determination. From a police perspective, however, it is also thought to be the least desirable and least convenient method. Further, like the testing of urine specimens, it provides an opportunity for the arrested person to recheck the blood test. If found to be erroneous, the validity of the police test can be attacked by re-testing the exact specimen taken by police.

Breath testing, again from a police perspective, is the most convenient means of alcohol concentration determination. In regard to the issues of accuracy and reliability of breath testing, however, there continues to be a heated debate among scientists. Moreover, under current procedures for breath testing in Texas, breath samples are not preserved for subsequent checks of the initial test's validity. Indeed, for purposes of breath testing, if you are an innocent person and your breath test results show you to be intoxicated, then the chances of showing error in the prosecution's case against you are literally "gone with the wind".