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.
To identify a subsequent medically necessary laboratory test on the same day of the same previous laboratory test
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 of test
For any reason when a normal one time result is required
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
Documentation must support the use of the modifier
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, two subsequent blood tests were ordered and performed on the same date of service.
Lab services examples:
Line 1 = 84132
Line 2 = 84132 91