Q&A: Differentiating between poisoning, adverse effects, underdosing, toxic effects

Q: In what ways are poisoning, adverse effects, underdosing, and toxic effects different?

A: There are several definitions for poisoning, one of which is when a drug or toxin is taken in error, overdosed (accidentally or intentionally), taken via the wrong route, or improperly administered. Essentially, the patient does not take their medication exactly as prescribed. Maybe they doubled up on the dosage, or they also drank alcohol/used an illegal substance when they took their medicine. Maybe the patient had a cold and instead of calling their provider, they self-medicated with Tylenol and cold medicine to alleviate the cold symptoms, causing the prescribed drug to react negatively with the non-prescribed drugs. Maybe the patient experienced pain but because they had no pain medicine, they took a family member's pain medication and had a reaction to it. All of these scenarios would be considered a poisoning. ICD-10-CM codes for poisonings are found in categories T36–T50 with fifth/sixth character 1, 2, 3, or 4, depending on the intent, whether accidental, intentional, assault, or undetermined.

An adverse effect occurs when a patient takes their medication exactly as prescribed—correct drug, correct dosage, and correct route—but for whatever reason, they have an adverse reaction to the medication. For example, a patient might be prescribed an antibiotic, and that particular antibiotic causes an adverse effect despite being taken as instructed, such as diarrhea from taking Augmentin®. Another example is an anaphylactic reaction due to prescribed penicillin, which a lot of people are allergic to. In these scenarios when an adverse effect is present, the effect is coded first (e.g. diarrhea, anaphylaxis, rash), followed by a T36–T50 drug code with fifth/sixth character 5.

Underdosing is exactly as it sounds. The patient is prescribed a certain medication, but they took less than what is required. This could occur when they are confused and forget to take their medicine, they go on a trip and forget to bring their medicine, or they cannot afford their medication and intentionally do not take it. Let’s look a more specific example: An 83-year-old woman has cognitive issues due to a stroke and decides not to take her blood pressure medication for a few days because she makes it up in her mind that she feels well; yet, she begins to take it again on day four when she starts to feel unwell due to rising blood pressure. If she were to go into a hypertensive emergency, the condition would be coded first, then a code from categories T36¥T50 with fifth/sixth character 6 for the medication that she did not take properly, and finally a Z code to indicate the cause behind her underdosing. Code assignments can tell a lot about a patient’s story if conditions are very clearly documented, particularly for underdosing, as there are very specific codes for such scenarios.

Toxic effect is a classification of a condition caused by ingestion or contact with a harmful, nonmedical substance and is generally categorized by the timing of the exposure and the nature of the damage. Acute toxicity is an immediate reaction based upon a single, short-term exposure to a high concentration of a toxic substance, such as alcohol overconsumption or poisoning from carbon monoxide. Symptoms can include nausea, vomiting, headache, dizziness, confusion, skin rash, and trouble breathing. Chronic toxicity results from repeated or long-term exposure, often to lower concentrations of a toxin. Symptoms could be delayed, appearing months or even years after exposure. Examples include lung cancer from secondhand smoke and chronic organ damage from heavy metal exposure. Codes for toxic effects are found in categories T51–T65.

Clear documentation will be necessary for coders to select the most appropriate category of codes, as it not only influences specific code assignments but also impacts the sequencing of many of these scenario types.

Editor’s note: This Q&A originally appeared in JustCoding and was excerpted from the HCPro webinar, “Beyond the Bottle: ICD-10-CM Coding Poisoning, Adverse Effects, and Underdosing with Accuracy and Clarity,” presented by Leigh Poland, RHIA, CCS, CDIP, CIC, vice president of coding services at AGS Health.