Just recently I posted "The Carry-over Effect: Lack of Blanks between tests leads to false positive or inflated BAC results" where we discussed the carry-over effect in Blood testing in DUI cases.
One of the possible places for carry-over effect is when an auto-pipetter is used in an autodiluter. Pennsylvania has some labs that in their Pennsylvania DUI testing use these devices.
(Above an auto-diluter)
(pictured above: how the autodiluter works)
The autodiluter is designed to take a precise portion of the blood sample and add into it a very precise amount of internal standard, which is blood testing for Blood Alcohol Content in DUI cases is most typically n-propanol. Below is a video of it in action.
In-between samples neither the tubing or the syringe that draws up the blood and eventually dispenses the mix of the blood and the internal standard is changed.
So how do we know that there is not carry-over?
The only way would be to make a blank in-between each sampling. But it is not done. What is done is serial dilution. Serial dilution is just simply flushing several cycles of internal standard through the device before sampling another unknown.
So why the picture of a flushing toilet Justin?
Does flushing the toilet two times, three times or even twenty times make the water desirable to drink?
Of course not!
Yet, this is sort of what happens with an autodiluter as described above.
So yet again, I simply say:
As an illustration, I draw your attention to a past post as a concrete example for this discussion. In "Highest reported BAC .708: I call Shenanigans", we discussed an extremely high reported BAC result. Much like our example, would you like to be the next test sample after that superhigh result? I would think not.
How about we start doing things in a scientifically responsible manner and run blanks in-between unknowns????
-Justin J. McShane, Esquire, Pennsylvania DUI Attorney
I am the highest rated DUI Attorney in PA as Rated by Avvo.com
Board Certified Criminal Trial Advocate
By the National Board of Trial Advocacy
A Pennsylvania Supreme Court Approved Agency