Question: When and how should we use external cause codes? New Mexico Subscriber Answer: You should use ICD-10-CM external cause codes as secondary codes when the additional information about the patient’s condition is relevant to treatment and patient care. You should never sequence an external cause code as the first-listed or principal diagnosis, according to the ICD-10-CM Official Guidelines for Coding and Reporting. External cause codes can tell healthcare providers treating the patient the following helpful information: Coding example: A 5-year-old girl falls from the jungle gym on the school playground and suffers a 2.0-cm cut on her right eyelid. The ophthalmologist performs a simple repair. You should report 12011 (Simple repair of superficial wounds of face, ears, eyelids, nose, lips and/or mucous membranes; 2.5 cm or less) linked to a primary diagnosis of S01.111 (Laceration without foreign body of right eyelid and periocular area) and a supplementary diagnosis of W09.2XXA (Fall on or from jungle gym, initial encounter).