T38.2X6A Underdosing of antithyroid drugs, initial encounter

ICD-10-CM T38.2X6A: Underdosing of antithyroid drugs, initial encounter

ICD-10-CM code T38.2X6A is an active diagnosis concept representing the initial encounter for underdosing of antithyroid drugs. It falls under the parent concept T38.2X6 and is classified with the semantic type of Injury or Poisoning. Antithyroid drugs treat thyrotoxicosis associated with hyperthyroidism. 1 2

Plain-language overview

Code T38.2X6A is an active terminology concept named underdosing of antithyroid drugs, initial encounter, and it is classified under the semantic type of Injury or Poisoning. 1

What this code represents

The diagnosis T38.2X6A is a narrower concept of the parent code T38.2X6, which is titled underdosing of antithyroid drugs, and it holds an active record status in the ICD-10-CM version 2026 terminology. 1

Clinical context

Antithyroid drugs are used to treat thyrotoxicosis associated with hyperthyroidism, and patients with Graves’ disease may receive a prolonged course of these medications to try and induce disease remission. 2

Antithyroid drugs may be administered in a titration regimen where a high starting dose is gradually reduced over weeks to months depending on the patient's response to the treatment. 2

Coding details

The ICD-10-CM definitions manual lists T38.2X6A as underdosing of antithyroid drugs, initial encounter, alongside a distinct subsequent encounter code for underdosing of antithyroid drugs. 1 3

Documentation considerations

The CMS definitions manual distinguishes the underdosing of antithyroid drugs, initial encounter from subsequent encounters and from accidental, intentional self-harm, or assault poisoning by antithyroid drugs. 3

What the sources add

While the terminology record defines the code's structural hierarchy and semantic type, the clinical literature explains that antithyroid drugs are a treatment modality for Graves’ hyperthyroidism, providing context for the medication class involved. 1 2

The CMS definitions manual lists T38.2X6A alongside various other initial and subsequent encounter codes for antithyroid drug issues, confirming its inclusion in the broader billing classification system. 3

Sources

1. ICD-10-CM T38.2X6A terminology record — National Cancer Institute Enterprise Vocabulary Services; accessed 2026-07-27.
2. Bookshelf — ncbi.nlm.nih.gov; accessed 2026-07-27.
3. ICD-10-CM/PCS MS-DRG v39.0 Definitions Manual — cms.gov; accessed 2026-07-27.