Modifier 91, What you need to know
Modifier 91 Repeat clinical diagnostic laboratory test is used to report the same lab test when performed on the same patient, on the same day, to obtain subsequent test results.
As per CPT definition, in the course of treatment of the patient, it may be necessary to repeat the same laboratory test on the same day to obtain subsequent or multiple test results. Under these circumstances, the laboratory test performed can be identified by its usual procedure number and the addition of modifier 91.
Modifier 91 causes a lot of confusion when differentiating its use from that of modifier 59 Distinct procedural service. When reporting lab procedures, modifier 59 is used when the same lab procedure is done, but different specimens are obtained, or the cultures are obtained from different sites.
As per CPT(R) guidelines, modifier 91 may not be used when tests are rerun to confirm the initial results, due to testing problems with specimens or equipment or for any other reason when a normal, one-time, reportable result is all that is required. This modifier may not be used when other code(s) describe a series of test results eg: Glucose tolerance tests, evocative/suppression testing. This modifier may only be used for laboratory test(s) performed more than once on the same day on the same patient.
If multiple tests are run, but a single code describes the test, only one code should be reported and modifier 91 would not apply.
For example, if 82951 Glucose; tolerance test (GTT), 3 specimens (includes glucose) includes three specimens. Therefore, if three specimens were obtained during the encounter, only 82951 would be reported in such a case.