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.