Direct answer: CLIA in medical billing refers to the federal certification requirements that apply to facilities performing laboratory testing on human specimens. When required for a laboratory service, the facility must hold the appropriate CLIA certificate and report its 10-character CLIA identification number correctly on the claim. Certain Medicare-designated waived tests also require modifier QW.
Reviewed October 2, 2026 using current Centers for Medicare & Medicaid Services guidance. Laboratories should verify requirements with CMS, their State Agency, Medicare Administrative Contractor, and individual payers.
What Does CLIA Mean in Medical Billing?
CLIA stands for the Clinical Laboratory Improvement Amendments. CMS administers the program to help ensure that laboratory test results are accurate, reliable, and timely.
CLIA generally applies when a facility examines human specimens such as blood, tissue, or bodily fluid to assess health or diagnose, prevent, or treat disease. A physician office performing point-of-care tests can therefore be considered a laboratory for CLIA purposes, even when laboratory testing is not its primary business.
CLIA certification and medical billing are connected because Medicare and other payers may verify that:
- The laboratory has an active CLIA certificate.
- The certificate permits the complexity of testing performed.
- The reported CLIA number belongs to the testing location.
- The claim includes the CLIA number when required.
- Modifier QW is present when required for a waived test.
Who Needs a CLIA Certificate?
A facility generally needs a CLIA certificate if it performs even one applicable test on a human specimen and reports patient-specific results for health assessment, diagnosis, prevention, or treatment.
CMS identifies some exceptions, including certain forensic testing, research testing that does not report patient-specific results used for treatment, specimen-collection-only facilities, and some employment drug testing. Facilities should confirm their specific circumstances with their State Agency.
New York and Washington operate state laboratory programs that are exempt from the federal CLIA program. Laboratories in those states should contact the appropriate state authority for instructions.
Types of CLIA Certificates
The certificate must correspond to the highest level of test complexity performed at the laboratory.
| Certificate | Purpose |
|---|---|
| Certificate of Waiver | For laboratories performing only tests categorized as waived. |
| Provider-Performed Microscopy Procedures Certificate | For specified microscopy procedures performed by an authorized practitioner during a patient visit. It also permits waived testing. |
| Certificate of Registration | Temporarily permits nonwaived testing while a laboratory applying for compliance or accreditation awaits its initial survey. |
| Certificate of Compliance | For moderate- or high-complexity testing after CMS or a State Agency determines that the laboratory complies with applicable requirements. |
| Certificate of Accreditation | For moderate- or high-complexity testing when the laboratory is accredited by a CMS-approved accreditation organization. |
CMS states that CLIA certificates are generally valid for two years. Laboratories must keep their certificate information current and follow the requirements associated with their certificate type.
What Is a CLIA Identification Number?
CMS assigns a unique 10-character CLIA identification number to a certified laboratory. Billing staff should use the number for the location where the testing was actually performed.
A group with multiple testing locations may need a separate certificate and identification number for each location, subject to CMS rules. Do not automatically use the organization’s primary-office CLIA number for every service location.
Where Does the CLIA Number Go on a Claim?
CMS instructs professionals to report the CLIA certification number in Item 23 of the paper CMS-1500 claim when it is required for the laboratory service.
For an electronic 837P claim, the CLIA number is reported using the appropriate REF segment in Loop 2300 or Loop 2400 with the CLIA qualifier. Billing software and clearinghouses may display these fields differently, so practices should verify their claim mapping before transmission.
Item 23 can also be used for information such as a prior authorization or referral number. CMS notes that the field can contain only one condition on a paper claim. Follow the applicable payer or Medicare Administrative Contractor instructions when more than one identifier is needed.
When Is Modifier QW Required?
Modifier QW identifies certain laboratory tests that Medicare recognizes as waived under CLIA. A laboratory with a Certificate of Waiver or qualifying Provider-Performed Microscopy certificate must append QW to applicable waived-test HCPCS codes when CMS requires it.
Do not assume that every waived test uses QW or rely permanently on an old code list. CMS issues quarterly Clinical Laboratory Fee Schedule and CLIA updates that identify:
- New laboratory HCPCS codes
- Codes subject to CLIA edits
- Tests approved as waived
- Codes requiring modifier QW
- Deleted or changed codes
Check the current CMS update or your Medicare Administrative Contractor’s guidance before submitting the claim.
Common CLIA-Related Claim Problems
Missing or incorrect CLIA number
A claim may fail payer edits when the required CLIA number is missing, entered incorrectly, or associated with a different testing location.
Expired or inactive certificate
The certificate should be active for the date of service. Billing teams should monitor expiration dates and confirm that CMS and the State Agency have current contact information.
Testing beyond the certificate’s scope
A Certificate of Waiver permits only waived testing. Moderate- or high-complexity testing requires the appropriate nonwaived certification and compliance with additional personnel, quality, and proficiency-testing requirements.
Missing modifier QW
When CMS designates a waived-test code as requiring QW, omitting the modifier may prevent the claim from passing Medicare’s CLIA edits.
Wrong service location
The CLIA number should correspond to the location that performed the test. Problems can occur when claims automatically populate the organization’s main laboratory number even though testing occurred elsewhere.
Certificate data does not match enrollment records
Changes involving the facility name, address, ownership, laboratory director, certificate type, or testing menu may require notification to the State Agency or updates to payer enrollment records.
How to Apply for a CLIA Certificate
- Determine the highest complexity of testing the facility intends to perform.
- Complete Form CMS-116, the CLIA application for certification.
- Send the application to the State Agency for the state where the laboratory is located.
- Follow instructions regarding fees, inspections, accreditation, and supporting information.
- Wait for authorization before performing patient testing when required.
- Keep the laboratory’s contact information and certificate details current.
CMS transitioned CLIA certificates and fee coupons to an electronic system in 2026. Laboratories need a valid email address on file and must pay applicable certification and survey fees online.
CLIA Billing Checklist
- Confirm that the laboratory has an active certificate.
- Verify that the certificate covers the highest test complexity performed.
- Use the CLIA number assigned to the actual testing location.
- Confirm whether the laboratory code is subject to a CLIA edit.
- Check whether CMS requires modifier QW for the billed code.
- Place the CLIA number in CMS-1500 Item 23 when required.
- Map electronic claims to the appropriate 837P REF segment.
- Confirm that the NPI, service location, payer enrollment, and CLIA records agree.
- Review quarterly CMS laboratory-code updates.
- Retain the current certificate and supporting compliance records.
Frequently Asked Questions
Does every medical practice need a CLIA certificate?
No. A practice generally needs certification when it performs applicable testing on human specimens. A facility that only collects or prepares specimens without performing testing may not be considered a laboratory under CLIA.
Does every laboratory claim require a CLIA number?
Report the CLIA number when it is required for the laboratory service and payer. CMS identifies Item 23 on the CMS-1500 and the appropriate REF segment on the 837P for reporting the number.
Is modifier QW required for every waived test?
No. Use QW when CMS identifies it as required for the specific waived-test code. Review the current CMS quarterly laboratory update rather than relying on an outdated static list.
How long is a CLIA certificate valid?
CMS states that CLIA certificates are generally effective for two years. Certificate holders must meet renewal, fee, inspection, and information-update requirements that apply to their certificate type.
Can a physician office perform moderate- or high-complexity tests?
Yes, but it must obtain the appropriate certificate and meet the applicable personnel, quality-control, proficiency-testing, and inspection or accreditation requirements.
Where can a practice verify its CLIA certificate?
CMS provides certificate and laboratory demographic information through its Quality, Certification and Oversight Reports system. Practices can also contact their State Agency or accreditation organization.
Official CMS Sources
- CMS Clinical Laboratory Improvement Amendments overview
- CMS Getting Started with CLIA
- CMS certificate types and test complexity
- CMS-1500 and 837P Item 23 guidance
- CMS Clinical Labs Information Center
Need Help Preventing Laboratory Claim Denials?
Accurate certification data, code selection, modifier use, and claim-field mapping help prevent avoidable laboratory denials. Learn more about our medical billing and coding services and denial management support, or contact us to discuss your practice’s needs.
