2026 ICD-10-CM Diagnosis Code T57.91XAToxic effect of unspecified inorganic substance, accidental (unintentional), initial encounter

ICD-10-CM Codes›S00–T88›T51-T65›T57

ICD-10-CM T57.91XA
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

T57.91XA is a billable ICD-10-CM diagnosis code for toxic effect of unspecified inorganic substance, 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 adverse reaction to inorganic chemical. 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

ICD-10-CM Code
T57.91XA
Billable Status
Yes — Valid for Submission
Code Describes
Toxic effect of unspecified inorganic substance, accidental (unintentional), initial encounter
Short Description
Toxic effect of unsp inorganic substance, accidental, init
Parent Code
T57.91
Toxic effect of unspecified inorganic substance, accidental (unintentional)

Code Classification

ChapterS00–T88Injury, poisoning and certain other consequences of external causes
SectionT51-T65Toxic effects of substances chiefly nonmedicinal as to source
CategoryT57Toxic effect of other inorganic substances
This CodeT57.91XAToxic effect of unspecified inorganic substance, accidental (unintentional), initial encounter

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Adverse reaction to inorganic chemical

Coding GuidelinesGuidance

The appropriate 7th character is to be added to each code from block Toxic effect of other inorganic substances (T57). 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.

CCSR EXT020
External cause codes: intent of injury, accidental/unintentional
Default principal diagnosis: inpatient No · outpatient No
CCSR EXT015
External cause codes: poisoning by non-drug
Default principal diagnosis: inpatient No · outpatient No
CCSR INJ023
Toxic effects, initial encounter
Default principal diagnosis: inpatient Yes · outpatient Yes

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.

SubstanceAccidentalSelf-harmAssaultUndeter­minedAdverse
Effect		Under­dosing
Inorganic substance NECT57.91T57.92T57.93T57.94––

Convert T57.91XA to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
989.9 Tox eff nonmed subst NOS
ApproximateCombination The match is approximate, and more than one code can be needed to describe the source diagnosis. Confirm with contextual judgment.
ICD-9-CM
E866.8 Acc pois-solid/liq NEC
ApproximateCombination The match is approximate, and more than one code can be needed to describe the source diagnosis. Confirm with contextual judgment.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About T57.91XAOverview

Is T57.91XA a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report toxic effect of unspecified inorganic substance, accidental (unintentional), initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What does the 7th character A in T57.91XA mean?

The final character A marks the initial encounter: use it while the patient is receiving active treatment for toxic effect of unspecified inorganic substance, accidental (unintentional), such as an emergency visit or first evaluation.

What MS-DRG does T57.91XA group to?

When toxic effect of unspecified inorganic substance, 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 T57.91XA?

Under the General Equivalence Mappings, toxic effect of unspecified inorganic substance, accidental (unintentional), initial encounter converts to ICD-9-CM 989.9 (tox eff nonmed subst NOS) and E866.8 (acc pois-solid/liq 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.