What is the purpose of modifier 91?

Modifier 91 is used specifically in scenarios where laboratory tests are repeated on the same day for the same patient, and those tests are deemed clinically necessary. This modifier indicates that the repeated tests were necessary due to changes in the patient's condition or to confirm the initial results. It helps convey to payers that the repetition of the test was not merely a matter of standard procedure, but was performed based on medical necessity.

The importance of modifier 91 lies in its role in ensuring accurate coding and billing for healthcare services. When tests must be repeated to obtain more accurate or adjusted results, modifier 91 clarifies the rationale for these actions, thereby justifying the additional charges associated with the repeated tests.