How do you approach a conversation with a patient with a markedly positive PETH (>200 ug/L) who is insistent that they do not consume any alcohol?  

Falsely positive PETh results are very rare. A possible cause is transfusion of PRBC from a donor who was a drinker. False positives from lab error are possible, so repeating in a few days after patient denial is worth it. The endogenous production of small amounts of alcohol by gut microorganisms h...