In the course of treating a treatment, it may be necessary to repeat the same laboratory test on the same day to obtain subsequent (multiple) test results. Modifier 91 Repeat clinical diagnostic laboratory test is used to indicate that different levels of service were provided for different specimens. The cytopathologic report must be clear as to why the same test was repeated on the same day.

Modifier 91 is not appropriate when a test is repeated on the same day to:

  • Confirm results
  • Test problems of the specimen
  • Test problems of the equipment
  • Perform multiple tests on the same specimen

In addition to being careful about modifier 91 use, you must be diligent in your code selection. It is inappropriate to append modifier 91 to a procedure and/or HCPCS level II code when another procedure code better describes the test being performed, or when the procedure code describes a series of tests, only one of which is being repeated.