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| There are a few goals with a BAC test. One if the BAC is close to a key threshold to get the number lowered below that threshold to decrease sentencing guidelines. Here is how the typical Seattle dui blood test is calculated. |
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| Two known samples are placed inside the lab instrument. If these test within 6% above or below then the lab instrument is said to be calibrated correctly. If not then the machine must be recalibrated by an outside firm and the lab technician cannot perform the lab test. |
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| The lab technician then places the sample on the machine and a reading is given. For a serum sample this is usually reduced by a number approximately 18-20%. For a whole blood sample no reduction is made. Then result is then reduced by the margin for error which is usually in the 5-6% area and then the BAC is calculated based upon this number. |
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| The critical factor here is that the margin for medical certainty is usually two standard deviations. This is the 95% confidence interval; disregard the high side of the confidence interval and the result is 2.5% chance that the number is less than this. Remember all of this is based upon statistics and all of it is based upon the hospital that the prosecution has chosen to perform the test correctly. |
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| Therefore if the Seattle dui charge is based upon a BAC of .0825 or .1525 the defense can make the case that there is still a 2.5% chance that the BAC is below this number based upon the prosecutions own evidence. To get to under 1% the hospital would have to use three standard deviations and to get to less than .25% chance the hospital would have to use 4 standard deviations. So based upon the use of statistics a successful argument can be made to the jury that the BAC is actually .005 BAC less than the test states. |
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| Another interesting thing about Serum tests is that they are based upon a conversion as well. The defense should be able to use the prosecutions own doctor to make claims about how dehydration, anemia and other blood conditions could affect the results of this test. |
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| Also for Serum Blood Tests a subpoena should be filed immediately to retest the blood sample at a different lab. If a blood preservative was not added to the blood sample prior to testing then the hospital will be unable to supply the test. This gives grounds to suppress the blood test because the sample was not preserved giving the defense the ability to retest the sample. |
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| For Whole Blood Tests careful considerations should be made to chain of custody issues. Most Whole blood samples in Seattle dui cases are sent to outside labs. Many of these labs are in different states. Depending upon the number of people at the lab that had custody of the sample from the mail room on must testify that this sample never left their custody. Bringing in one or multiple lab technicians from a lab out of state will add considerable cost to the prosecution. |
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