Why are cutoff values different from different labs?
Re cutoffs values: The primary cutoff is a lab procedure to assure technical accuracy of the test. Depending on the technique and its accuracy the cutoff level reduces potential error from intrinsic variations from the test procedure. For these purposes labs believe they can substantiate the quality and validity of testing using a cutoff of 100 ng/ml. There is always a tension between sensitivity and speicificity, false positives and false negatives. The cutoff values should not be so low that the test picks up extraneous alcohol intake (food, mouthwash, etc) resulting in “false positives.” On the other hand it is not desirable for the threshhold to be too high, which reduces sensitivity, and would create more false negatives. Also, we know that very little alcohol (.02-.06%) is metabolized by non-oxidative glucuronidation. The “standard drink” in the USA is 14gm (about 1.5oz of vodka, 12oz beer, 5oz wine). Thus the small fraction of alcohol actually metabolized this route means that a
