2026 ICD-10-CM Diagnosis Code T58.8X1AToxic effect of carbon monoxide from other source, accidental (unintentional), initial encounter
T58.8X1A is a billable ICD-10-CM diagnosis code for toxic effect of carbon monoxide from other source, 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. 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 exposure to carbon monoxide
- Accidental exposure to carbon monoxide in industry
- Accidental poisoning by carbon monoxide from blast furnace gas
- Accidental poisoning by carbon monoxide from incomplete combustion of fuels in industrial use
- Accidental poisoning by CO - kiln vapor
- Carbon monoxide poisoning from fire
- Poisoning by carbon monoxide from aircraft while in transit, without accident to aircraft
- Poisoning by carbon monoxide from aircraft while in transit, without accident to aircraft, member of ground crew or airline employee injured
- Poisoning by carbon monoxide from aircraft while in transit, without accident to aircraft, occupant of unpowered aircraft, except parachutist, injured
- Poisoning by exhaust gas in aircraft
Coding GuidelinesGuidance
The appropriate 7th character is to be added to each code from block Toxic effect of carbon monoxide (T58). 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
Carbon Monoxide Poisoning
Carbon monoxide (CO) is a gas that has no odor or color. But it is very dangerous. It can cause sudden illness and death. CO is found in combustion fumes, such as those made by cars and trucks, lanterns, stoves, gas ranges and heating systems. CO from these fumes can build up in places that don't have a good flow of fresh air.
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert T58.8X1A to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About T58.8X1AOverview
Is T58.8X1A a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report toxic effect of carbon monoxide from other source, accidental (unintentional), initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What does the 7th character A in T58.8X1A mean?
The final character A marks the initial encounter: use it while the patient is receiving active treatment for toxic effect of carbon monoxide from other source, accidental (unintentional), such as an emergency visit or first evaluation.
What MS-DRG does T58.8X1A group to?
When toxic effect of carbon monoxide from other source, 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 T58.8X1A?
Under the General Equivalence Mappings, toxic effect of carbon monoxide from other source, accidental (unintentional), initial encounter converts to ICD-9-CM 986 (tox eff carbon monoxide) and E868.8 (acc pois-carbn monox 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.
