2026 ICD-10-CM Diagnosis Code T56.811AToxic effect of thallium, accidental (unintentional), initial encounter
T56.811A is a billable ICD-10-CM diagnosis code for toxic effect of thallium, 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 by thallium. 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 by thallium
- Accidental poisoning by thallium compounds
- Thallium poisoning
- Thallium sulfate toxicity
Coding GuidelinesGuidance
The appropriate 7th character is to be added to each code from block Toxic effect of metals (T56). 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.
Convert T56.811A to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About T56.811AOverview
Is T56.811A (Toxic effect of thallium, accidental (unintentional)) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report toxic effect of thallium, accidental (unintentional), initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What does the 7th character A in T56.811A mean?
The final character A marks the initial encounter: use it while the patient is receiving active treatment for toxic effect of thallium, accidental (unintentional), such as an emergency visit or first evaluation.
What MS-DRG does T56.811A group to?
When toxic effect of thallium, 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 T56.811A?
Under the General Equivalence Mappings, toxic effect of thallium, accidental (unintentional), initial encounter converts to ICD-9-CM 985.8 (toxic effect metals NEC) and E866.4 (acc poison-metals 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.
