Numeric designation preceded by the letter “E” that is a classification of International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) coding for external causes of injury rather than disease. E codes are also used in coding adverse reactions to medications and should not be used as a principal diagnosis because the insurance carrier will reject the claim. Their use identifies causes of injury and poisoning and can be important in obtaining payment from insurance payers. The index for the E codes is located in Volume 2, following the Table of Drugs and Chemicals. Also known as the Supplementary Classification of External Causes of Injury and Poisoning (E800-E999) .