I'm retired RN and one late summer night I was working the ER and two teenage girls were brought in by their parents demanding a drug test because their daughters hands were blue. The doc noticed they had on fancy jeans that appeared to be new. He asked them what they had done that evening. They had been to a friend's house for a BBQ and when they got home their hands were blue. The doc then asked what they had to drink and they replied cokes. He then asked if they their drinks were in a cup or can or bottle and they replied a can. He asked what they did when their drinks began to sweat and they replied that they had wiped their hands on the legs of their jeans. The parents were so surprised at his questions and a little put out as well. I explained that we saw this several times a year because the girls were wiping their wet hands on the jeans they were turning blue. The girls had not noticed it at the friends house because they were outside on the patio at dusk with very little light. I did commend the parents for their diligence in making sure their girls were drug free.