Modifier CW

Our office manager says that when we do a strep or flu swab to code the swabs with a CW modifier so that we can charge the patient the difference after the EOB is received. Basically, the test costs $17 approximately but only getting paid around $10-11. She is wanting to charge the patient the difference and remembers doing this at one time. I can't find anything on this modifier though. Can anyone help me or point me in the right direction? Thank you!

re: Modifier CW

All Medicare reimbursed laboratory tests are subject to the direct billing requirement, meaning tests must be billed directly to Medicare by the laboratory or physician performing the test. Laboratories must also accept assignment when billing Medicare for their services, meaning the laboratory must accept the Medicare reimbursement as payment in full for any covered laboratory test. It is not permissible to “balance”-bill Medicare patients for any additional amounts.
http://www.cms.gov/Regulations-and-Guidance/Legislation/CLIA/Downloads/waivetbl.pdf

re: Modifier CW

What about commercial insurances?