Uncertainty in Blood Testing

A major shift in how the Michigan State Lab reports alcohol blood test results has recently occurred due to the efforts of our fellow criminal defense colleagues in pressing the lab to testify about what the error rates are in blood testing.  No scientific test is perfect and there is always a margin of error.  In the context of a blood test, the Michigan State Lab now reports the uncertainty level of a blood draw.  What this boils down to is that the lab offers a number which represents how far off the test could be and still considered valid, along with a  percentage, which represents the lab's prediction for how many times out of a thousand that they would expect the result of the blood test to be in the range.

How this works when we deal with these situations is that the client will have a blood draw of a .09.  The Lab will then provide in their report a range of a .02.  Also, a confidence level of 99.7% is given.  What this means is that the forensic scientist from the lab is 99.7% sure that the blood alcohol level tested is somewhere between a .07 to a .11.  And the forensic scientist also believes that in three out of every thousand blood draws they've tested, the result they found is not within that range.  Given the fact that these blood testers have tested hundreds of thousands of blood samples, the amount of blood draws that are completely incorrect is stunning.

Drunk driving trial lawyer Jim Amberg likens these error rates to playing Russian roulette with somebody's freedom.  And that argument has resulted in favorable verdicts for his clients.