Laboratory Modifiers 59 and 91: Correct Use and Coding Guidance

Apr 21, 2026 | Provider Resource

Community First Health Plans is providing clarification on the appropriate use of laboratory modifiers 59 and 91. These modifiers are valid for many laboratory services and may be required when multiple laboratory services described by a single CPT® code are performed for the same patient on the same date of service by the same provider.

Correct modifier use supports accurate claims processing, CMS compliance, and reduces claim denials.

Modifier 59 – Distinct Procedural Service

Modifier 59 is used to indicate that a laboratory service is separate and distinct from another laboratory service billed on the same date of service, even when the same CPT® code is reported.

Appropriate use includes situations such as:

The same laboratory test performed on different specimens
Testing performed on different species or strains
Distinct laboratory services that produce separately reportable results

CPT® guidance notes that modifier 59 may be reported when the same procedure code is used for testing different specimens, species, or strains, and when separate results are reported for each.

Modifier 59 should not be used:

When a more specific modifier is available
To routinely bypass National Correct Coding Initiative (NCCI) edits
When services are duplicative and not distinct

Think: different service, different circumstance.

Modifier 91 – Repeat Clinical Diagnostic Laboratory Test

Modifier 91 is used when the same laboratory test is repeated on the same patient, same date of service, to obtain subsequent results that are medically necessary for patient management.

Appropriate use applies only when all criteria are met:

Same CPT® code
Same patient
Specimen collected more than once on the same day
Repeat testing is medically necessary and clearly documented

Examples include repeated laboratory tests performed at different intervals during the same day for ongoing monitoring, such as serial blood glucose or electrolyte testing.

Think: same test, repeated for a valid clinical reason.

When Modifiers 59 or 91 Should Not Be Used

According to CPT® guidance, modifiers 59 and 91 should not be appended to laboratory codes in the following circumstances:

Reruns performed to confirm test results
Testing repeated due to specimen or equipment issues
When another procedure code describes a series or panel test
When the procedure code itself represents a series of tests
When a one‑time result is required and no subsequent result is clinically necessary

Documentation Requirements

For both modifiers, documentation must clearly support use of the modifier, including:

Medical necessity
Distinct specimens or collection times, when applicable
Clinical rationale for distinct or repeat testing

Key Takeaway

Modifier 59: Use for distinct laboratory services
Modifier 91: Use for a medically necessary repeat of the same laboratory test

Modifiers should only be applied when documentation clearly supports their use.

Action:

Providers are encouraged to share this information with their staff. If you have any questions about this notice, please email Provider Relations at ProviderRelations@cfhp.com or call 210-358-6030. You can also contact your Provider Relations Representative directly.

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