Is there a chance of alcohol dissipating on a blood retest?

Just adding to Mr. Bogan's response, you never know. I've had cases where blood retests came back lower than what the DA's lab reported where the retest was done within 2 months of the original test. If an individual at the time of the stop agreed to take a PAS breat test at the scene of the stop and it came back at or about .20 and the blood test came back at about the same, unless a retest came back much lower or there was a problem with the way the blood draw was done, the preservative in the tube was insufficient, the blood was not refrigerated before the original test, or the blood type did not match the individual's blood type, it would be a tough case to fight. It doesn't cost too much to have blood retested so it is worth trying, especially if it number does not fit the amount of alcohol consumed during a certain period of time. There are different consequences in DUI cases where the blood alcohol is less than .20 and those that are .20 or higher. You should discuss all of this with an experienced DUI attorney in your area.

The blood sample should be properly maintained with the right amount of preservative, and refridgerated. Speak to a DUI attorney in your area. It's possible that a blood retest (often referred to as a blood split) could come back with lower or higher results. If the results vary enough either way it can be used as a defense.

Yes, it is possible for the alcohol level in a blood sample to dissipate, but only likely if the sample is left open, topper off, so that the alcohol within evaporates. It is most likely that alcohol level will increase rather than decrease due to numerous reasons. Is dissipation factored in? No, two different tests on two different GC machines with most likely very dissimilar columns, controls and other factor differences.