You are thinking of modifier 51, where, because the same provider in the same session, does more than one procedure, and overhead can already be attributed to the first procedure, payers feel justified in paying 100% for the first procedure, 50% for the second, and 20% (?) for the third, etc . In the case of the 3 analytes, you are performing three tests represented by the same CPT code, however, each test is distinct. Therefore, I would code the first with no modifier and the next 2 with modifier 59. [Modifier 91 is used for repeat tests on the same day to, for example, obtain subsequent readings for comparison.]