Otolaryngology Coding Alert

Learn to distinguish between adverse effect and poisoning.

Sometimes, deciphering which ICD-10-CM code to report for an occurrence of drug toxicity can be tricky, so the process is best broken down into individual parts. As an otolaryngology coder, you know that there are a lot of moving parts in the diagnostic coding process — and we’re here to break down the steps for determining the appropriate codes to report for encounters when a patient presents with unfortunate side effects from taking prescribed medication using a clinical example.

In situations like this, context is absolutely key. Use the advice and techniques in this case scenario to help better equip you to handle coding any case of drug toxicity that comes your way.

Clinical example: A patient arrives for an evaluation and management (E/M) visit following chemotherapy for metastatic squamous neck cancer. The reason for the visit states “throat pain from vomiting following chemotherapy.” Documentation confirms the patient received the chemotherapeutic agent prescribed, and it was administered per the physician’s order.

Which ICD-10-CM codes should you report?

Step 1: Understand Drug Toxicity Classifications

Codes in categories T36-T65 are combination codes that identify the substance the patient took as well as the intent. Your code search begins at the Table of Drugs and Chemicals, and landing on the correct code hinges on you pinpointing the type of drug toxicity:

• Adverse effect: Problem that arises after taking a drug that has been correctly prescribed and properly administered
• Poisoning: Reaction to the improper use of a medication
• Underdosing: Taking less of a medication than is prescribed
• Toxic effect: Ingestion or contact with a harmful substance

Based on these definitions, we can deduce that the patient is experiencing an adverse effect of the chemotherapeutic agent.

“The key to coding from the Table of Drugs and Chemicals in ICD-10-CM is understanding the differences between these definitions, knowing the difference between adverse effect, poisoning, underdosing, and toxic effect,” says Barbara J. Cobuzzi, MBA, CPC, COC, CPC-P, CPC-I, CENTC, CPCO, CMCS, of CRN Healthcare in Tinton Falls, New Jersey.

Step 2: Know How to Find Adverse Effect of Chemo Code

Turn to the Table of Drugs and Chemicals section in your ICD-10-CM book. There, you can search under the terms “antineoplastic” or “cancer chemotherapy drug regimen” to find the correct set of codes. You will then select the code listed under “adverse effect.” Lastly, you’ll refer to the Tabular List to verify the full code, which in this case is T45.1X5A (Adverse effect of antineoplastic and immunosuppressive drugs, initial encounter).

Careful: You do not want to use the code listed under “poisoning, accidental (unintentional).” Since the correct drug was prescribed and the correct dosage was administered, these effects are a known and expected result of chemotherapy treatment. If, on the other hand, the patient received a much greater dosage than the doctor had prescribed, or the wrong substance was given, you could report code T45.1X1A (Poisoning by antineoplastic and immunosuppressive drugs, accidental (unintentional), initial encounter).

Step 3: Follow Coding Guidelines

In order to code this scenario correctly, you need to have a firm grasp of the known side effects of chemotherapy. Since nausea and vomiting are typical side effects for patients being administered chemotherapy, you will take a different route of coding this situation than if the effects were unintended or unexpected. Take a look at Section I.C.19.e.5.a of the 2023 ICD-10-CM guidelines:

When coding an adverse effect of a drug that has been correctly prescribed and properly administered, assign the appropriate code for the nature of the adverse effect followed by the appropriate code for the adverse effect of the drug (T36-T50). The code for the drug should have a 5th or 6th character “5” (for example T36.0X5-) Examples of the nature of an adverse effect are tachycardia, delirium, gastrointestinal hemorrhaging, vomiting, hypokalemia, hepatitis, renal failure, or respiratory failure.

Based on this guideline, you should code the vomiting first, followed by the adverse effect of chemotherapy code. For emesis, you will report code R11.10 (Vomiting, unspecified) and for the adverse effect of the chemotherapy, you will use code T45.1X5A (Adverse effect of antineoplastic and immunosuppressive drugs, initial encounter).

Step 4: Keep the General Coding Guidelines in Mind

Even though the throat pain is the underlying reason for the visit, the pharyngalgia is a result of the vomiting. ICD-10-CM guideline I.B.5 states that “if a causal condition is known, then the code for that condition should be sequenced as the principal or first-listed diagnosis.” Since throat pain is not a typical symptom of vomiting, you may include R07.0 (Pain in throat) as a third and final diagnosis.

Step 5: Don’t Forget the Z Code

The 2023 ICD-10-CM code set expands your options in category Z79 (Long term (current) drug therapy). This code boost allows you to identify the type of chemotherapy being administered to the patient. If the specific drug is documented, you can now assign the appropriate code from the Z79.63- (Long term (current) use of chemotherapeutic agent) group. Use code:

• Z79.630 (Long term (current) use of alkylating agent) for chlorambucil, cisplatin, and cyclophosphamide
• Z79.631 (Long term (current) use of antimetabolite agent) for methotrexate, 5-fluorouracil, 6-mercaptopurine, and cytarabine
• Z79.632 (Long term (current) use of antitumor antibiotic) for bleomycin, doxorubicin, and mitomycin C
• Z79.633 (Long term (current) use of mitotic inhibitor) for paclitaxel, plant alkaloids, vinblastine, and vincristine
• Z79.634 (Long term (current) use of topoisomerase inhibitor) for etoposide, irinotecan, and topotecan

Step 6: Factor in Z79.63- for Chemo Side Effects

Don’t forget about the impact chemo can have on E/M leveling. Chemotherapy, and the cancer itself, can be enough to bump an E/M service potentially to 99215 (Office or other outpatient visit for the evaluation and management of an established patient … high level …). That’s because drug therapy requiring intensive monitoring for toxicity is an example of the high risk of complications of patient management element of medical decision making (MDM), while the patient’s condition may also rise to the high level of number and complexity of problems addressed element of MDM. So, reporting a code such as Z79.63- may support the higher-level E/M.

Note: Be on the lookout for when the Centers for Medicare & Medicaid Services (CMS) adds these codes to the National Coverage Determination (NCD) and Local Coverage Determination (LCD) lists and articles. “Ordering lab work to monitor patients on these newly represented medications may not be covered if reported with Z79.8 or Z79.899,” cautions Halee Garner, CPC, CPMA, CCA, certified coder for Digestive Health Partners in Asheville, North Carolina.