Modifier 90- Reference (Outside) Laboratory

Modifier 90 is used when laboratory procedures are performed by a reference (outside) laboratory rather than by the billing provider or facility.

What is Modifier 90?

Modifier 90 identifies laboratory tests that are performed by an outside or reference laboratory. It is appended to the laboratory procedure code when the billing provider submits a claim for testing that was actually performed by another qualified laboratory. Modifier 90 helps accurately identify the entity that performed the laboratory service and supports proper claim processing based on payer requirements.

When to Use Modifier 90

• A laboratory test is performed by an outside or reference laboratory.

• The billing provider is permitted to bill for the reference laboratory service.

• The laboratory procedure is eligible for Modifier 90.

• Documentation identifies the performing laboratory.

Billing Example

A physician collects a blood specimen in the office but sends it to an independent reference laboratory for specialized testing. When permitted by the payer, the laboratory procedure is reported with Modifier 90 to indicate the test was performed by an outside laboratory.

Documentation Tips

• Document the name of the performing reference laboratory.

• Maintain the laboratory order and test results.

• Verify payer billing requirements for reference laboratory services.

• Ensure the reported laboratory code matches the service performed.

Common Denial Reasons

• Modifier 90 is reported on an ineligible service.

• Documentation does not identify the performing laboratory.

• Payer requires the performing laboratory to bill directly.

• Incorrect laboratory procedure code is reported.

Related Modifiers

Modifier 91

Modifier 92

Modifier AS

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