Hospital Blood Tests in DUI Cases
Enzyme assay is the method used most commonly by hospital laboratories and the analysis is performed on serum or plasma samples, rarely on whole blood. The hospital serum or plasma ethanol test is used as a clinical screening test to determine if a patient has altered mental status due to ethanol, some other condition (such as closed head trauma), or a combination of ethanol and some other medical condition.
The hospital test results are not reliable as forensic evidence for the following reasons:
- In a trauma setting, arterial samples are often drawn instead of venous samples;
- The sample does not have a complete chain of custody;
- The sample is serum or plasma, not whole body;
- The sample is analyzed by enzyme assay, a method associated with a high frequency of false positive results;
- The sample is usually analyzed once, not twice as required;
- The sample is not retained for subsequent re-analysis;
- Quality control measures are not usually in place to assure forensically reliable results; and
- The system allows for plus or minus 25 percent error, or a total error of 50 percent, well above the forensic standard of plus or minus 5 percent error.