Modifier 91 used to report repeat clinical laboratory tests.

What you need to know

Modifier 91 is used to report any repeat clinical diagnostic laboratory test being billed if:

• A single service (same CPT code) is ordered (for the same beneficiary)
• Specimen is collected more than once in a single day 
• The service is medically necessary

Appropriate use

To identify a subsequent medically necessary laboratory test on the same day of the same previous laboratory test

Inappropriate uses

• When there are testing problems with the specimen
• A more appropriate procedure code is available to describe a series test
• Rerun of a laboratory test is done to confirm results
• Testing problems with the equipment
• Procedure code describes a series or panels of test

Claim submission instructions

• Bill all services performed same day on the same claim
• Report each service on a separate line, with quantity of one and append 91 to the repeat procedure
• Document the use of the modifier in the medical record
• Review the medically unlikely edits to ensure proper coding and billing of units of service

Claim processing

A patient had multiple blood tests performed to check his potassium level after potassium replacement and low-dose insulin therapy. After the initial potassium value was measured, a subsequent blood test was ordered and performed on the same date of service. 

• Lab services examples:
  • Line 1 = 84132 
  • Line 2 = 84132 91