Modifier 91

Repeat clinical diagnostic laboratory test


This modifier is used to indicate a repeat laboratory procedure or service on the same day to obtain subsequent reportable test values.

Correct use

  • For necessary tests to obtain subsequent (multiple) test results
  • For tests performed on same patient on same day
  • Used with laboratory tests paid under clinical laboratory fee schedule

Incorrect use

  • May not be used when there are standard HCPCS codes available that describe the series of results (e.g., glucose tolerance tests, evocative/suppression testing, etc.)
  • May not be used when tests are rerun to confirm initial results; due to testing problems with specimens and equipment; or for any other reason when a normal, one-time, reportable result is all that is required
  • Does not replace modifiers such as RT, LT, 50, E1-E4, FA, F1-F9, TA, and T1-T9



Last Updated Dec 12 , 2022