Box 19 If Applicable Reserved for Local Use -
Use this area for procedures that require additional information, justification or an Emergency Certification Statement.
• This section may be used for an unlisted procedure code when explanation is required and clinical review is required.
• If modifier “-99” multiple modifiers is entered in section 24d, they should be itemized in this section.
All applicable modifiers for each line item should be listed.
• Claims for “By Report” codes and complicated procedures should be detailed in this section if space permits.
• All multiple procedures that could be mistaken for duplicate services performed should be detailed in this section.
• Anesthesia start and stop times.
• Itemization of miscellaneous supplies, etc.
Box 2. Services rendered to an infant may be billed with the mother’s ID for the month of birth and the month after only. Enter “Newborn using Mother’s ID”/ “(twin a) or (twin b)” in the Reserved for Local Use field (Box 19).
http://www.cms1500claimbilling.com/2016/04/for-what-box-19-reserved-for-local-use.html