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Modifier 90 (Reference to Outside Laboratory)

The 90 modifier is to be used when the billing laboratory refers a specimen to another lab for testing. In these cases, the billing lab is titled the “referring lab” while the lab that actually performed the test is the “reference lab.”

  • Only independent billing clinical laboratories (specialty 69) can bill with the 90 modifier. Sometimes a clinical diagnostic independent lab, place of service (POS) 81, refers a specimen to another lab for testing, where a modifier 90 is appended.
    • The billing entity must be designated as a specialty 69 in their provider enrollment record within the Provider Enrollment, Chain, and Ownership System (PECOS).
  • Must append modifier 90 to referred laboratory test code
    • Item 20 mark "Yes" = outside lab
    • Purchase price must be reflected under charges
    • Complete item 32 with NPI, name and address where test was performed
  • Appropriate modifier 90 claims include two different Clinical Lab Improvement Amendment (CLIA) numbers on electronic claims
    • Reflect billing provider information
    • Laboratory where services were performed (reference lab)
  • Bill claims with modifier 90 and without modifier 90 separately electronically on the same claim
  • If no purchased services, leave item 20 blank
  • When the lab submits claims, services both performed and referred may be billed on the same electronic claim. Regardless, of the services performed, whenever the 90 modifier is billed on a claim, the following information must be included.
Information Loop Field Identifier
Billing lab’s CLIA number 2300  REF02 X4
Reference lab’s CLIA number 2400 REF02 F4
Modifier 90 (Reference to Outside Laboratory)
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