Crime labs don't necessarily check for other substances in your blood - usually only if the cop suspects something or you've admitted to something. The California DOJ does check blood samples that come up less than .08% routinely. I don't know where their data is, but it could be interesting to know the results. Get a lawyer's advice right away from a nearby one.
I agree with both Michael and Josh, both of whom know their DUI stuff exceedingly well. The irony of the blood testing in this area is that even though they frequently and expensively test for other stuff if the BAC comes back less than .08, the one thing they never test for, even though it is inexpensive to do, is preservative level. So blood tests over .08% are quite fightable because of the government's lack of care and insight in that regard.
Most crime labs test for what is requested by the submitting agency. If there is a BAC test requested and its over the legal limit, most labs will stop there - unless requested otherwise. If a BAC test is requested and it is under the limit, then they will do an ELISA screen to test for commonly abused drugs. Each lab and each jurisdiction is going to be different. I can't comment on the Alameda lab - I can only speak in general terms.
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