In 2025, understanding how to properly report a CLIA number on CMS 1500 forms is more critical than ever for labs, providers, and billing teams. With increased payer scrutiny and evolving claims validation protocols, failing to include the CLIA number—or placing it incorrectly—can lead to costly denials. This article breaks down where to report the CLIA number, which claims require it, and what’s new in 2025 based on Medicare and commercial payer guidelines.
What Is a CLIA Number and Why It Matters in 2025
The Clinical Laboratory Improvement Amendments (CLIA) number is a unique identifier assigned to laboratories by CMS to certify compliance with federal lab testing standards. Any entity performing lab testing for diagnosis, prevention, or treatment of disease must hold a valid CLIA certificate.
As of 2025, billing for lab services without a valid CLIA number on the claim may result in rejections or post-payment audits, especially for waived or moderately complex tests. CMS’s CLIA program overview outlines these certification rules in detail.
Where to Put the CLIA Number on the CMS 1500 Form
According to updated CMS 2025 claim submission guidance, the CLIA number must be entered in:
- Box 23 of the CMS 1500 paper claim form (labeled “Prior Authorization Number”)—this box also accommodates CLIA numbers.
- For electronic claims (837P), the CLIA number is reported in the REF02 segment with REF01=QW.
Be sure the CLIA number is associated with the correct rendering or billing provider NPI, especially in multi-location or multi-specialty groups.
2025 CLIA Number Requirements: What’s New?
Several important updates in 2025 affect CLIA number reporting for lab services:
- Medicare contractors now cross-check CLIA numbers against their internal registry to validate location-specific certifications.
- Some commercial payers like UHC and Anthem have adopted automated edits that reject lab claims without valid CLIA numbers.
- CLIA-waived test claims (e.g., CPT 87811 for COVID-19) must continue to be billed with modifier QW and a matching CLIA number in Box 23.
Review payer-specific policies such as UnitedHealthcare’s billing requirements for lab services to stay compliant.
Which Lab Services Require the CLIA Number?
The following categories of lab tests typically require a CLIA number on the CMS 1500 form:
- CLIA-waived tests (billed with QW modifier)
- Moderately complex lab tests
- Any lab service reimbursed under Medicare Part B or Medicaid
Keep in mind that tests listed in the Clinical Laboratory Fee Schedule are closely monitored for CLIA compliance.
Common Errors to Avoid When Reporting CLIA Numbers
- Leaving Box 23 blank on paper claims when billing for lab tests
- Using an expired or incorrect CLIA number
- Submitting CLIA-required CPT codes without modifier QW (for waived tests)
- Entering the CLIA number in the wrong field on the 837P
Errors like these can result in payment delays, denial letters, and audit flags. For more insights on common denial reasons, be sure to review our dedicated guide.
Best Practices for CLIA Number Compliance
To ensure clean claims and faster reimbursements in 2025:
- Verify your facility’s CLIA certification status regularly on CMS.gov
- Ensure billing software maps CLIA numbers to the correct location and NPI
- Educate front-office and billing staff on CLIA requirements during onboarding
- Keep documentation of your CLIA certificate on file for all sites
Also, check out our CPT coding guidelines page for lab test-specific advice and reimbursement tips.
FAQ: CLIA Number on CMS 1500
Does every lab claim need a CLIA number?
No. Only tests categorized as CLIA-waived, moderately complex, or high-complexity require the CLIA number. Routine procedures like blood draws may not.
Can multiple providers share one CLIA number?
Only if they operate under the same certified lab site. Otherwise, each testing location must have its own valid CLIA certificate number.
What happens if I forget to include the CLIA number?
Your claim will likely be denied, especially by Medicare or major payers. This could trigger a compliance audit or payment recoupment request.
Conclusion
Including the CLIA number on CMS 1500 claims is a small step with major compliance and reimbursement implications in 2025. Whether you’re billing for waived COVID-19 tests or complex genetic panels, accurate placement of this number is essential. Stay current with payer rules, validate your certification status, and ensure your billing software supports CLIA reporting logic. For more guidance on optimizing your lab billing processes, visit our resources on prior authorization steps and ICD-10 coding tips.