Blood alcohol content
This recently updated thread from Testy Copy Editors is worth a read. It points out a couple of facts about blood alcohol content that are often wrong.
First, it's not a percentage. There's some math involved here that you can get at TCE, but it comes down to this: The measurement is of grams (of alcohol) per deciliter (of blood), and that doesn't work out to be a percentage. (Blood and alcohol each have a different densities from water.)
Second, it's a measurement of the alcohol content of the blood. A hyphen between blood and alcohol isn't necessary.