Don't forget about the modifier. Missing or incorrect usage of modifiers is the most common reason that claims are rejected by payors. Leave off a modifier, or put in the wrong one, and your claim may be denied or paid the wrong amount. Coding with Modifiers: A Guide to Correct CPT and HCPCS Level II Modifier Usage provides step-by-step guidance for the proper use of CPT and HCPCS modifiers. Also included are specific requirements for modifier usage in both professional service and hospital reporting.