Pathology/Lab Coding Alert

Question: I am still confused about when to append modifier QW to a lab test. What advice can you give me?

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Answer: Knowing when, and when not, to append modifier QW (CLIA waived test) to a lab test is often confusing, especially to those new to path/lab coding. But the following advice should help you get the coding right the next time you’re unsure if the lab test you are coding needs the modifier.

First, Know What a CLIA-Waived Test Is

Clinical Laboratory Improvement Amendments (CLIA) are regulations established by Congress to ensure lab tests on human material meet certain standards for accuracy and reliability across labs. CLIA issues a number of certificates to labs in every state except New York and Washington, which administer their own certification programs.

The CLIA-issued certification that is relevant to the QW modifier is known as the certificate of waiver (COW), which is “issued to a laboratory that performs only waived tests,” according to the Centers for Medicare & Medicaid Services (CMS). “Waived tests,” the CMS document goes on to say, “are categorized as ‘simple laboratory examinations and procedures that have an insignificant risk of an erroneous result.’” The U.S. Food & Drug Administration (FDA) reviews each test as it comes onto the market to determine whether it meets such standards, and if it does, it is placed on the CLIA-waived analytes list.

This list will tell you if a lab with a CLIA COW can perform a test on the list. However, not all CLIA-waived tests on the list require the QW modifier.

Then, Determine if the Test Requires the QW Modifier

To determine whether or not a particular test does take QW, you will need to consult the Clinical Laboratory Fee Schedule (CLFS), which is updated quarterly. Simply download the files for the quarter in which the service was provided, open the Excel file, and look up the CPT^Ò or HCPCS Level II code for the test. If the QW modifier appears in column C for that test, then you will append the modifier; if it doesn’t, you won’t.

Example: If your lab performs 85025 (Blood count; complete (CBC), automated (Hgb, Hct, RBC, WBC and platelet count) and automated differential WBC count), you will append QW. However, 85027 (Blood count; complete (CBC), automated (Hgb, Hct, RBC, WBC and platelet count)) does not take the QW modifier per the CLFS for Q4 of 2025.

And Pay Attention to These Caveats

First, as the CLFS is updated every quarter, it is important to consult the list for the appropriate quarter for the date of service (DOS) of a given test. Second, remember that some payers and states maintain their own lists of CLIA-waived tests, so always check with your insurer and state listing to confirm which tests are on their list.

The bottom line: Don’t use QW as a blanket modifier for all lab tests. If you append modifier QW to a code for a test that doesn’t require it, you’ll get a denial. Alternatively, if you forget to append the QW modifier on a test that does require it, you’ll get a denial, too.

Bruce Pegg, BA, MA, CPC, CFPC, Managing Editor, AAPC