I need some help! I have a question regarding modifier -91. If a provider (in the ER) orders a test (80053) and then orders another test, specifically looking at a lab individually (ie potassium or lab 80048) should mod -91 be applied? or should it only be applied to the exact same CPT code if it is reported a second time? I have looked at the definition of the use of -91 in the CPT book, and I am not sure if I am misunderstanding the definition, or if the lab tech is incorrect for applying the -91 on the different test and if a modifier is needed, would it be an -XU? I greatly appreciate any insight that anyone can provide.