2027 ICD-10-CM Diagnosis Code T56.1X4SToxic effect of mercury and its compounds, undetermined, sequela
T56.1X4S is a billable ICD-10-CM diagnosis code for toxic effect of mercury and its compounds, undetermined, 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 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 922 through 923. The code is exempt from POA reporting. Coders also document this condition as contact dermatitis caused by mercurial. 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
T56.1X4S is exempt from POA reporting on inpatient claims to general acute care hospitals. Review the other POA exempt codes in Toxic effects of substances chiefly nonmedicinal as to source (T51-T65).
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Contact dermatitis caused by mercurial
- Encephalopathy caused by heavy metal
- Poisoning caused by mercury
- Toxic encephalopathy caused by mercury
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 2027, published by CMS and the National Center for Health Statistics.
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to T56.1X4S: its own notes plus those printed at T56, block T51-T65, and Chapter 19. A note printed at a category, block or chapter applies to every code under it.
Includes
Further defines, or gives examples of, the content of the category.
- toxic effects of fumes and vapors of metals
- toxic effects of metals from all sources, except medicinal substances
Excludes1
Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.
- contact with and (suspected) exposure to toxic substances (Z77.-)
Excludes2
Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.
Use Additional Code
Add a second code, after this one, to fully describe the condition.
- code to identify any retained foreign body, if applicable (Z18.-)
Notes
General instructions on how these codes are used.
- When no intent is indicated code to accidental. Undetermined intent is only for use when there is specific documentation in the record that the intent of the toxic effect cannot be determined.
- Use secondary code(s) from Chapter 20, External causes of morbidity, to indicate cause of injury. Codes within the T section that include the external cause do not require an additional external cause code
- The chapter uses the S-section for coding different types of injuries related to single body regions and the T-section to cover injuries to unspecified body regions as well as poisoning and certain other consequences of external causes.
7th Character
Every code in the category takes a 7th character from the listed values, with the placeholder X filling any empty positions before it.
- The appropriate 7th character is to be added to each code from category T56
- Ainitial encounter
- Dsubsequent encounter
- Ssequela this code
Source: CMS ICD-10-CM Tabular List. How to read instructional notes.
Referenced in Other NotesGuidance
Instructional notes printed at other codes that name T56.1X4S, its category, or a range that includes it.
Excludes1 2
These codes carry an Excludes1 note naming T56.1X4S: they are not reported together with it, unless the two conditions are unrelated.
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.
| Substance | Accidental | Self-harm | Assault | Undetermined | Adverse Effect | Underdosing |
|---|---|---|---|---|---|---|
| Corrosive NEC::sublimate | T56.1X1 | T56.1X2 | T56.1X3 | T56.1X4 | – | – |
| Ethyl::mercuric chloride | T56.1X1 | T56.1X2 | T56.1X3 | T56.1X4 | – | – |
| 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::chloride (ammoniated)::fungicide | 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 | – | – |
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 T56.1X4S to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About T56.1X4SOverview
What is the ICD-10 code for toxic effect of mercury and its compounds, undetermined, sequela?
The ICD-10-CM code for toxic effect of mercury and its compounds, undetermined, sequela is T56.1X4S (sometimes written as T561X4S). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
Is T56.1X4S (Toxic effect of mercury and its compounds, undetermined) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report toxic effect of mercury and its compounds, undetermined, sequela on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What does the 7th character S in T56.1X4S 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, undetermined itself has resolved, not the original event.
What MS-DRG does T56.1X4S group to?
When toxic effect of mercury and its compounds, undetermined, sequela is the principal diagnosis on an inpatient stay, it groups to MS-DRG 923, 922, with relative weights from 0.9980 to 1.6248 depending on complications. Higher weights mean higher Medicare reimbursement.
Is T56.1X4S 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, undetermined, sequela on inpatient claims. The code appears in the Toxic effects of substances chiefly nonmedicinal as to source (T51-T65) range of the CMS exempt list.
