QW is a HCPCS modifier defined as: CLIA waived test.  Append it to lab services that are on the CLIA waived test list.

Download the up to date list of CLIA waived tests from CMS's web site.  The link is the citation.  There are two issues:

• Some tests do not require the QW modifier, and may be denied if it is applied.  They are on the first page of the listing
• Some tests may be performed in many different ways.  For example, a glucose test can be performed with a test kit, or in a lab. There are different procedure codes for them.  Be sure that you select the code for the service you have performed.  Many of the tests on the list have the specific manufacter's name and the description along with the code

See also the related Codapedia article on CLIA waived tests, which provides more detail.