2026 ICD-10-CM Diagnosis Code T59.7X1AToxic effect of carbon dioxide, accidental (unintentional), initial encounter
T59.7X1A is a billable ICD-10-CM diagnosis code for toxic effect of carbon dioxide, accidental (unintentional), initial encounter. The 7th character A marks it as an initial encounter code, used while the patient is receiving active treatment. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 917 through 918. Coders also document this condition as accidental poisoning from exhaust gas of moving motor vehicle on road. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under External cause codes: intent of injury, accidental/unintentional; External cause codes: poisoning by non-drug; and Toxic effects, initial encounter.
Code Identity
Code Classification
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Accidental poisoning from exhaust gas of moving motor vehicle on road
- Exposure to carbon dioxide
- Exposure to gaseous substance
- Toxic effect of carbon dioxide
Coding GuidelinesGuidance
The appropriate 7th character is to be added to each code from block Toxic effect of other gases, fumes and vapors (T59). Use the following options for the applicable episode of care:
- A - initial encounter
- D - subsequent encounter
- S - sequela
Source: ICD-10-CM Official Guidelines for Coding and Reporting, FY 2026, published by CMS and the National Center for Health Statistics.
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Table of Drugs and ChemicalsClinical
Substances in the Table of Drugs and Chemicals that reference this code family. Always confirm in the Tabular List before coding.
Patient EducationClinical
Poisoning
A poison is any substance that is harmful to your body. You might swallow it, inhale it, inject it, or absorb it through your skin. Any substance can be poisonous if too much is taken. Poisons can include:
Read the full article at MedlinePlus
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Convert T59.7X1A to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About T59.7X1AOverview
Is T59.7X1A (Toxic effect of carbon dioxide, accidental (unintentional)) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report toxic effect of carbon dioxide, accidental (unintentional), initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What does the 7th character A in T59.7X1A mean?
The final character A marks the initial encounter: use it while the patient is receiving active treatment for toxic effect of carbon dioxide, accidental (unintentional), such as an emergency visit or first evaluation.
What MS-DRG does T59.7X1A group to?
When toxic effect of carbon dioxide, accidental (unintentional), initial encounter is the principal diagnosis on an inpatient stay, it groups to MS-DRG 917, 918, with relative weights from 0.8571 to 1.5684 depending on complications. Higher weights mean higher Medicare reimbursement.
What is the ICD-9 equivalent of T59.7X1A?
Under the General Equivalence Mappings, toxic effect of carbon dioxide, accidental (unintentional), initial encounter converts to ICD-9-CM 987.8 (toxic eff gas/vapor NEC) and E869.8 (acc poison-gas/vapor NEC). The mapping is approximate, so confirm the match fits the documentation.
Footnotes
[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.
