In an intoxication assault case, what person would be the most appropriate witness to testify that the level of alcohol tested by the hospital (expressed in mg/dL) equals an alcohol concentration above the legal limit?

I've done the math from Richard Alpert's book and know that the concentration level is .167. But who testifies? DPS chemist? Trooper? Medical Doctor? Technician from the hospital lab?

You need a real toxicologist who understands the conversion of serum to whole blood and the 'issues' in doing such a conversion, as well as the testing technique.

I agree. You need a toxicologist. The others folks mentioned likely don't understand all of the caveats of such testimony.

Where would you find such a toxicologist?

I called my friendly neighborhood DPS crime lab. They had some toxicologists on staff, and I was able to speak with one about the case. Big thank you to the Crime Lab folks!