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Modifier 91

Modifier 91 Description and Billing Use

Plain-language description

Reports a medically necessary repeat laboratory test, not a repeat caused by specimen or equipment problems or simple confirmation.

How modifier 91 is used

Modifier 91 identifies a medically necessary repeat clinical diagnostic laboratory test. It does not apply to a rerun caused by specimen or equipment problems or to simple confirmation without a supported clinical reason.

Before reporting this modifier

  1. 1. Confirm the current official or licensed definition and payer acceptance.
  2. 2. Identify the exact claim circumstance the modifier communicates.
  3. 3. Make the code, setting, related services, and medical record consistent.
  4. 4. Check NCCI, global surgery, component, DME, ABN, or drug rules that apply.
  5. 5. Do not append a modifier only to force an edit override.
LessonStudy the related billing ruleOfficial sourceReview current CMS guidance

This is a workflow summary, not a licensed CPT definition or claim-specific coding instruction. Verify the code set and payer rule effective for the date of service.