Modifier reference · Updated Aug 6, 2026
Modifier QW
Modifier QW tells Medicare a laboratory test was performed with a test system waived under CLIA. It lets the claim pass the CLIA certificate edit for a site holding a Certificate of Waiver; it does not change the payment amount.
What CLIA waiver means Copy link
Every laboratory testing site — including a physician office laboratory — needs a CLIA certificate to perform tests on human specimens, and the certificate level controls which tests it may legally run. A Certificate of Waiver covers only tests categorized as waived: simple test systems with a low risk of an erroneous result, like dipstick urinalysis or a fingerstick INR meter. The site's CLIA number goes on every laboratory claim.
When QW is required Copy link
CMS identifies waived tests in a quarterly-updated list sent to the Medicare contractors. Some waived tests have their own HCPCS codes; others share a code with the non-waived version of the test and must carry modifier QW to be recognized as the waived version. Prothrombin time is the everyday example — billed as CPT 85610 with QW when run on a waived device. A small set of long-waived tests predating the modifier convention does not use it.
What QW does not change Copy link
Payment. Waived tests are paid under the Clinical Laboratory Fee Schedule, and the QW and non-QW versions of a code carry the same fee-schedule amount in CMS's files — the modifier satisfies a certification edit, nothing more. It also does not affect the visit billed alongside the test: a same-day lab does not require modifier 25 on an E/M code, so a nurse visit with an in-office INR check keeps its eligibility for the G2211 add-on.
Frequently asked Copy link
Does modifier QW change how much Medicare pays?
No. The QW and non-QW versions of a code carry the same Clinical Laboratory Fee Schedule amount; the modifier exists so the claim passes the CLIA certificate edit.
Which certificate does a practice need to bill QW tests?
At minimum a CLIA Certificate of Waiver, with the CLIA number on the claim. A Certificate of Waiver covers only waived tests — anything beyond that list needs a higher certificate level.
Does a QW lab test affect billing the office visit?
No. A same-day clinical lab does not require modifier 25 on the visit, and it does not block the G2211 ongoing-care add-on.
Sources Copy link
- CMS Medicare Claims Processing Manual (Pub. 100-04)
- CMS Clinical Laboratory Improvement Amendments (CLIA)
- CMS Clinical Laboratory Fee Schedule
Written from primary CMS sources — see how we source, compute, and verify everything on this site.
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