T59.91XD Toxic effect of unspecified gases, fumes and vapors, accidental (unintentional), subsequent encounter

ICD-10-CM T59.91XD: Toxic effect of unspecified gases, fumes and vapors, accidental (unintentional), subsequent encounter

ICD-10-CM code T59.91XD is an active terminology concept representing the toxic effect of unspecified gases, fumes, and vapors from an accidental or unintentional exposure. It is designated for a subsequent encounter, indicating the patient is receiving routine care during the healing or recovery phase after active treatment has ended. 1 2

Plain-language overview

This diagnosis code represents an injury or poisoning event involving unspecified gases, fumes, and vapors, indicating the patient is receiving routine follow-up care during the recovery phase after active treatment has ended. 1 2

What this code represents

The code T59.91XD is an active concept with the preferred name of toxic effect of unspecified gases, fumes and vapors, accidental (unintentional), subsequent encounter, and it belongs to the semantic type of Injury or Poisoning. 1

The parent concept for this specific diagnosis code is T59.91, which broadly captures the toxic effect of unspecified gases, fumes and vapors, accidental (unintentional), without specifying the encounter type. 1

Coding details

The seventh character D identifies a subsequent encounter, which signifies that the patient is receiving routine care during the healing or recovery phase after the active treatment phase for the injury has ended. 2

Official coding guidelines state that if the intent of the cause of an injury or poisoning is unknown or unspecified, the intent is coded as unintentional rather than using external cause codes for undetermined intent. 2

Documentation considerations

Toxic effects of nonmedicinal substances, including carbon monoxide and other gases, are captured using diagnosis codes in the T51 through T65 range, which encompass various injury and poisoning mechanisms. 2

What the sources add

While the terminology record defines the code hierarchy and semantic type, the national health statistics report provides the operational rule dictating that the seventh character D designates routine recovery care. 1 2

A phecode mapping list includes this exact subsequent encounter code among a broader group of toxic effect codes that also capture initial encounters, sequelae, intentional self-harm, assault, and undetermined intent. 5

Sources

1. ICD-10-CM T59.91XD terminology record — National Cancer Institute Enterprise Vocabulary Services; accessed 2026-07-27.
2. National Health Statistics Reports — cdc.gov; accessed 2026-07-27.
3. Vaping coding guidance 2019 — cdc.gov; accessed 2026-07-27.
4. Bookshelf — ncbi.nlm.nih.gov; accessed 2026-07-27.
5. Phecode 987 · Cancer PRSweb — csg.sph.umich.edu; accessed 2026-07-27.
6. Article - Billing and Coding: Oximetry Services (A57205) — cms.gov; accessed 2026-07-27.