Part of CPT and HCPCS coding are modifiers. Modifiers are two digit codes that indicate a modification to clarification to the CPT or HCPCS. Modifiers can be found in the CPT and HCPCS books in Appendix A. In many instances the proper use of a modifier can avoid claim denials. Understanding modifiers is very important.
There are three kinds of modifiers and understanding the differences is imperative as it directly relates to their usage. The first are evaluation and management (E&M) modifiers, these can only be used on E&M services. Remember that E&M are office visits only, these do not include diagnostic testing or surgery, please review the evaluation and management section in CPT coding earlier in this writing.
The second type is procedure modifiers. These modifiers only apply to procedures including diagnostic and therapeutic and surgery. Included in this group are location modifiers, such as RT for right and LT for left. Finally the last group is general modifiers that may be used on either type of service.
On the CMS 1500 form, modifiers are listed in the service line just after the service code, like this: (this sample uses the modifier 25 next to 99213. Please note, a modifier 25 generally indicates the presence of another CPT code on the same claim. This is not depicted in the image because this image is strictly to show you the location of the modifier fields.)
As you can see, there are 4 modifier spots. On a paper claim form, you can only have 4 modifiers. It is pretty rare to need more than 4 modifiers per claim line or service line.
Follow this link to see a complete list of modifiers and their descriptions from Medicare: Modifiers for Billing