Summary of Health Insurance and Claims Processing

## Introduction This study guide covers ICD-10-CM coding rules and practical application for drug-related events: **adverse effects**, **poisonings**, **underdosing**, and **toxic effects**. It explains how to select and sequence codes from categories T36–T65 and related nature-of-condition codes, with examples and tips to apply in clinical coding scenarios. > Definition: Adverse effect — an unwanted or harmful effect resulting from a drug correctly prescribed and properly administered. ## Overview: Key ICD-10-CM concepts - Codes in categories **T36–T65** are combination codes for substances related to adverse effects, poisonings, toxic effects, and underdosing. These codes often include the external cause/intent as a fifth or sixth character, so no additional external cause code is required for these events. - Sequence a T36–T65 code first, followed by codes that describe the **nature of the condition** (e.g., R40.20 for coma, L50.0 for hives), with specific exceptions noted below. ### Coding categories and intent characters - Fifth or sixth character indicates intent where applicable: - 1 = accidental (unintentional) - 2 = intentional self-harm - 3 = assault - 4 = undetermined - 5 = adverse effect (drug correctly prescribed and properly administered) - 6 = underdosing - 9 = unspecified > Definition: Poisoning — harmful effects due to improper use of medication (eg, overdose, wrong substance or route, errors) or interactions producing toxicity. ## 1. Adverse Effect (fifth/sixth character "5") - Use when the drug was correctly prescribed and properly administered and an unwanted effect occurs. - Coding order: **nature-of-condition code** (diagnosis/symptom) first, then the **T code with ...5** for the adverse effect. - Examples of manifestations: tachycardia, delirium, GI hemorrhage, vomiting, hypokalemia, hepatitis, renal failure, respiratory failure. Example - Hives due to penicillin taken as prescribed (initial encounter): - T36.0X5A (adverse effect, penicillin, initial encounter) - L50.0 (hives) Coding tip - The term **intoxication** may indicate alcohol involvement or medication accumulation. If alcohol intoxication, assign a poisoning code. If accumulation from correct use (e.g., Coumadin buildup), assign adverse effect code. ## 2. Poisoning (intent-specific codes) - Use for incorrect use: overdose (intentional or accidental), wrong substance given or taken in error, wrong route, drug interactions causing toxicity when misuse or error occurred. - Assign the appropriate T36–T50 code with an intent character (1–4) for poisoning. - If intent is unknown or unspecified, **default to accidental intent**. Use undetermined only when documentation states intent cannot be determined. - Always add codes for **manifestations** of the poisoning (e.g., R40.20 for coma). - If there is a concurrent diagnosis of **substance abuse or dependence**, code that separately in addition. Examples - Coma due to overdose of barbiturates from attempted suicide (initial encounter): - T42.3X2A (poisoning by barbiturates, intentional self-harm, initial encounter) - R40.20 (coma) Common poisoning scenarios - Prescription or administration errors (provider, nurse, patient) - Intentional overdose (self-harm) - Nonprescribed drug taken with correctly prescribed drug causing interaction - Interaction between drugs and alcohol ## 3. Underdosing (fifth/sixth character "6") - Underdosing = taking less than prescribed or discontinuing medication on patient’s own initiative. - Assign a T36–T50 code with character "6" for underdosing. Documentation that the patient reduced or stopped medication is sufficient; change in condition is not required. - Codes for underdosing should **never** be used as principal/first-listed codes. Instead, code the underlying medical condition as principal; follow with the T code for underdosing. - Use noncompliance codes (Z91.12–Z91.14) or complication-of-care codes (Y63.8–Y63.9) to indicate intent w