Modifier 91
CPT modifier indicating a repeat clinical diagnostic laboratory test performed on the same day to obtain subsequent reportable test values.
1 min read · Last reviewed May 23, 2026
At a glance
- Category
- Billing
- Primary sources
- 1
- Workspace handoff
- ask d3 →
Where this comes up
This shows up in revenue-cycle work — claim scrubbing, charge entry, posting, A/R follow-up, and month-end close. Billers and practice managers hit this term when reconciling a payment, working a denial queue, or auditing why a claim aged past 60 days.
Full definition
What it is in practice
CMS recognizes modifier 91 when the same test is repeated for clinical reasons (not because of confirming a result). Cannot be used to indicate equipment malfunction.
How it shows up in your practice
Document the clinical reason for the repeat test. Common in serial glucose, troponin, or ABG monitoring.
Sources
- CMS — Modifiershttps://www.cms.gov/medicare/coding-billing/modifiers
Verify modifier 91 use in Ask D3
Open ask d3 →Related terms
- BillingModifier 76CPT modifier indicating a repeat procedure or service by the same physician or other qualified health care professional.
- BillingCLIA (Clinical Laboratory Improvement Amendments)Federal regulations applicable to all U.S. facilities or sites that test human specimens for health assessment or to diagnose, prevent, or treat disease.
D3rx is a healthcare-billing and compliance research aid maintained by D3rx Inc. Articles are drafted by an LLM (Anthropic Claude) against primary HHS, OCR, CMS, eCFR, NIST, and state-regulator publications, and reviewed for restraint and source fidelity by the D3rx team.
Reviewer status: a named credentialed reviewer (CHC, CHPC, or healthcare attorney) is being engaged. Until that engagement is finalized, this page does not claim credentialed review.
Related across the archive
- GlossaryModifier 76CPT modifier indicating a repeat procedure or service by the same physician or other qualified health care professional.
- GlossaryCLIA (Clinical Laboratory Improvement Amendments)Federal regulations applicable to all U.S. facilities or sites that test human specimens for health assessment or to diagnose, prevent, or treat disease.
- GlossaryModifier 22CPT modifier indicating increased procedural services requiring substantially greater work than usually required.
- GlossaryModifier 24CPT modifier indicating an unrelated E/M service performed by the same provider during a postoperative global period.
- GlossaryModifier 26CPT modifier indicating the professional component of a procedure.
- GlossaryModifier 50CPT modifier indicating a bilateral procedure performed at the same operative session.
- GlossaryModifier 51CPT modifier indicating multiple procedures performed at the same session by the same provider.
- BillingAWV + Problem Visit Same Day: How to Bill CorrectlyYes, you can bill AWV and a problem visit the same day. Here's how to do it correctly with modifier -25.
This glossary entry is a research aid for billing and compliance staff. It does not provide legal, medical, or financial advice and does not replace counsel. References cited link to primary sources at HHS, OCR, CMS, eCFR, NIST, and the relevant payer or industry body.