2026 ICD-10-CM Diagnosis Code T56.1X1SToxic effect of mercury and its compounds, accidental (unintentional), sequela
T56.1X1S is a billable ICD-10-CM diagnosis code for toxic effect of mercury and its compounds, accidental (unintentional), sequela. The 7th character S marks it as a sequela code, which reports a problem that remains after the original condition has resolved. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 922 through 923. The code is exempt from POA reporting. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Poisoning/toxic effect/adverse effects/underdosing, sequela.
Code Identity
Code Classification
Present on Admission (POA)Billing
T56.1X1S is exempt from POA reporting on inpatient claims to general acute care hospitals. Review other POA exempt codes.
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Accidental exposure to inorganic mercury compound
- Accidental exposure to metallic mercury
- Accidental exposure to organic mercury compound
- Accidental poisoning by mercury and/or mercury compound and/or mercury vapor
- Accidental poisoning by mercury compounds
- Accidental poisoning by mercury vapor
- Accidental poisoning by organic mercurials
- Acrodynia due to mercury poisoning
- Acute mercury nephropathy
- Allergic contact gingivitis caused by mercury
- Allergic gingival disease
- Allergic gingivitis
- Chronic mercury nephropathy
- Chronic toxic interstitial nephritis
- Chronic tubulointerstitial nephritis caused by heavy metal
- Heavy-metal-induced tubulointerstitial nephritis
- Hypersensitivity gingivitis
- Infantile mercury poisoning
- Inorganic mercury poisoning
- Mercurial tremor
- Mercurialentis
- Minamata disease
- Organic mercury poisoning
- Toxic effect of mercury and/or mercury compound
- Toxic encephalopathy caused by monomethyl mercury
- Toxic polyneuropathy
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.
Clinical InformationClinical
Toxic Polyneuropathy
polyneuropathy that is caused by exposure to toxins.Chronic Toxic Polyneuropathy
neuropathy affecting multiple nerves that is caused by prolonged exposure to toxic substances.
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.
| Substance | Accidental | Self-harm | Assault | Undetermined | Adverse Effect | Underdosing |
|---|---|---|---|---|---|---|
| Fulminate of mercury | T56.1X1 | T56.1X2 | T56.1X3 | T56.1X4 | – | – |
| Mercury, mercurial, mercuric, mercurous (compounds) (cyanide) (fumes) (nonmedicinal) (vapor) NEC | T56.1X1 | T56.1X2 | T56.1X3 | T56.1X4 | – | – |
| Mercury, mercurial, mercuric, mercurous (compounds) (cyanide) (fumes) (nonmedicinal) (vapor) NEC::ammoniated | T56.1X1 | T56.1X2 | T56.1X3 | T56.1X4 | – | – |
| Mercury, mercurial, mercuric, mercurous (compounds) (cyanide) (fumes) (nonmedicinal) (vapor) NEC::anti-infective | T56.1X1 | T56.1X2 | T56.1X3 | T56.1X4 | – | – |
| Mercury, mercurial, mercuric, mercurous (compounds) (cyanide) (fumes) (nonmedicinal) (vapor) NEC::anti-infective::local | T56.1X1 | T56.1X2 | T56.1X3 | T56.1X4 | – | – |
| Mercury, mercurial, mercuric, mercurous (compounds) (cyanide) (fumes) (nonmedicinal) (vapor) NEC::anti-infective::systemic | T56.1X1 | T56.1X2 | T56.1X3 | T56.1X4 | – | – |
| Mercury, mercurial, mercuric, mercurous (compounds) (cyanide) (fumes) (nonmedicinal) (vapor) NEC::anti-infective::topical | T56.1X1 | T56.1X2 | T56.1X3 | T56.1X4 | – | – |
| Mercury, mercurial, mercuric, mercurous (compounds) (cyanide) (fumes) (nonmedicinal) (vapor) NEC::chloride (ammoniated) | T56.1X1 | T56.1X2 | T56.1X3 | T56.1X4 | – | – |
| Mercury, mercurial, mercuric, mercurous (compounds) (cyanide) (fumes) (nonmedicinal) (vapor) NEC::chloride (ammoniated)::fungicide | T56.1X1 | T56.1X2 | T56.1X3 | T56.1X4 | – | – |
| Mercury, mercurial, mercuric, mercurous (compounds) (cyanide) (fumes) (nonmedicinal) (vapor) NEC::diuretic NEC | T56.1X1 | T56.1X2 | T56.1X3 | T56.1X4 | – | – |
| Mercury, mercurial, mercuric, mercurous (compounds) (cyanide) (fumes) (nonmedicinal) (vapor) NEC::fungicide | T56.1X1 | T56.1X2 | T56.1X3 | T56.1X4 | – | – |
| Mercury, mercurial, mercuric, mercurous (compounds) (cyanide) (fumes) (nonmedicinal) (vapor) NEC::organic (fungicide) | T56.1X1 | T56.1X2 | T56.1X3 | T56.1X4 | – | – |
| Mercury, mercurial, mercuric, mercurous (compounds) (cyanide) (fumes) (nonmedicinal) (vapor) NEC::oxide, yellow | T56.1X1 | T56.1X2 | T56.1X3 | T56.1X4 | – | – |
Patient EducationClinical
Mercury
Mercury is an element that is found in air, water and soil. It has several forms. Metallic mercury is a shiny, silver-white, odorless liquid. If heated, it is a colorless, odorless gas. It also combines with other elements to form powders or crystals. Mercury is in many products.
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert T56.1X1S to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About T56.1X1SOverview
Is T56.1X1S a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report toxic effect of mercury and its compounds, accidental (unintentional), sequela on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What does the 7th character S in T56.1X1S mean?
The final character S makes this a sequela code: it reports a lingering problem that remains after the toxic effect of mercury and its compounds, accidental (unintentional) itself has resolved, not the original event.
What MS-DRG does T56.1X1S group to?
When toxic effect of mercury and its compounds, accidental (unintentional), sequela is the principal diagnosis on an inpatient stay, it groups to MS-DRG 922, 923, with relative weights from 1.0177 to 1.7494 depending on complications. Higher weights mean higher Medicare reimbursement.
Is T56.1X1S exempt from POA reporting?
Yes. CMS lists this code among those exempt from present on admission reporting, so hospitals do not assign a POA indicator for toxic effect of mercury and its compounds, accidental (unintentional), sequela on inpatient claims.
What is the ICD-9 equivalent of T56.1X1S?
Under the General Equivalence Mappings, toxic effect of mercury and its compounds, accidental (unintentional), sequela converts to ICD-9-CM 909.1 (late eff nonmed substanc). 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.
