Question about Blood Alcohol Content

[kleinstadt1]

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I don't know what the others have said and I'm late to the show, but I'll inject this thread with what I know, which may not even be the answer.

When someone has blood drawn for the BAC test, the results come back as a number like 149.5. That translates to a BAC of .1495. I know this because I arrested a guy for a DUI related crash and had to get a search warrant for his lab results, where I then contacted the lab tech to ask him what the 149.5 meant.

And from my understanding, it was always .08%, not 8%.

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Incorrect. The 149.5 is 149.5mg/dL, and this is not interchangeable with BAC by %.

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Could you elaborate on this? Do you know what the conversion is?

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Confession: I'm being kind of a nit on this one.

The short answer is that there is no exact conversion.

Long, boring explanation: mg/dL is measured in serum, which is blood that has been spun down, removing all the cells. It is a weight (mg) per volume (dL) measurement.

BAC, or the % measurement, is the percent of alcohol by weight in a certain volume of whole blood, that is, blood with all the cells still in it.

100mL of whole blood weighs more than 100mL of serum.

Serum ethanol concentration and BAC are roughly interchangeable in the way you described, but may be off by up to 10% in a particular individual based on their red blood cell count, osmolality of serum, etc.

This makes no difference when you're tanked at 300mg/dL, obv. It may make a difference if it's a borderline driving 80mg/dL or something.