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 (multiple) test results. Under these circumstances, the laboratory test performed can be identified by its usual procedure number and the addition of modifier 91.
Note: This modifier may not be used when tests are rerun to confirm 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.