T70.3XXA ICD-10-CM Code: Caisson disease [decompression sickness], initial encounter

Coding instructions

Official Tabular Instructional Notes: the inclusion, exclusion and sequencing notes published for T70.3XXA in the official ICD-10-CM tabular list, quoted as published.

Source: CMS/CDC — ICD-10-CM Tabular ListRelease: FY2026Effective: October 1, 2025

Notes without a marker are published on T70.3XXA itself; “inherited from” names the category or block whose note applies here.

7th Character Guide

"The appropriate 7th character is to be added to each code from category T70"

• A — initial encounter (this page’s code)
• D — subsequent encounter
• S — sequela

How the encounter character is assigned. “Initial encounter” means the patient is receiving active treatment for the condition — it is not limited to the first visit, and a different or new provider giving active treatment still assigns it. “Subsequent encounter” covers care during the healing or recovery phase after active treatment. “Sequela” is for complications or conditions that arise as a direct result of the original condition.

ICD-10-CM Official Guidelines for Coding and Reporting, Section I.C.19.a (paraphrased by MedCoder).

Variant codes in this family

T70.3XXA, T70.3XXD, T70.3XXS

Character meanings are CMS's official 7th-character extensions for this family, as carried in each variant code's official description; variant codes are registry rows. The explanation of how the encounter character is assigned is MedCoder editorial, distinct from the official content above it.

Coder workflow for T70.3XXA

MedCoder structured workflow — derived from this code’s own official record

Before you code T70.3XXA

1. A 7th character is required in this family. Confirm the documented encounter: initial (active treatment), subsequent (healing or recovery phase), or sequela. This page’s code carries “A”. “Initial” means active treatment, not the first visit (Guidelines I.C.19.a).

   See the 7th Character Guide · Guide: 7th characters: initial, subsequent, sequela →

Choose the right path

1. Is the encounter phase documented — active treatment, healing or recovery, or a sequela?
   Yes → Assign the matching 7th character; the variant codes are in the 7th Character Guide.
   No → The code is invalid without its 7th character — query for the missing element.

Consider T70.3XXA. Then review the Code Also note, and confirm the code is valid for the date of service in the Verify section.

Documentation check

The provider’s diagnostic statement

Codes are assigned from the provider’s documented diagnosis, not from clinical criteria, test values or a medication list (Guidelines I.A.19).

Encounter type

Active treatment, healing or recovery phase, or sequela — the basis of the 7th character (Guidelines I.C.19.a).

Official instructions as workflow

• Code Also — related condition(6 notes)

  Coding workflow: Review the related condition when both are documented and the instruction applies. A Code Also note does not fix sequencing; the order follows the circumstances of the encounter.

  ReviewY92.523, Y92.21, Y92.52, Y92.01, Y92.81

  See the official tabular notes · Guidelines I.A.17

Coding decision scenarios

Pattern scenarios for this code’s structure — decision rules, not clinical cases

Every row is derived from this code’s own record — its title, tabular notes, 7th-character family and same-category siblings — with fixed MedCoder wording; nothing is inferred about a patient. The official notes and guideline text are in the sections each row links to, and they control.

Don’t confuse T70.3XXA with…

MedCoder analysis — pairs from this code’s official notes, distinctions written by MedCoder

The codes most likely to be picked instead of T70.3XXA — named in its own official notes, or sharing its laterality or encounter family — with what separates them and which documentation moves the case. Each links to the full comparison.

• T70.3XXD— Encounter relationship (Review)

  Same underlying diagnosis, different encounter phase.

  The same diagnosis at a different phase of care; one encounter takes one 7th character.

  What moves you there: Documentation of a subsequent encounter moves the case to T70.3XXD.

  Full comparison: T70.3XXA vs T70.3XXD →

• T70.3XXS— Encounter relationship (Review)

  Same underlying diagnosis, different encounter phase.

  The same diagnosis at a different phase of care; one encounter takes one 7th character.

  What moves you there: Documentation of a sequela moves the case to T70.3XXS.

  Full comparison: T70.3XXA vs T70.3XXS →

Relationships are read from this code's own official notes, its laterality siblings and its encounter family; the wording of each distinction is MedCoder editorial, and the documentation named in each “what moves you there” line is the official note phrase or sibling title itself. Source: CMS ICD-10-CM tabular instructional notes; ICD-10-CM Official Guidelines, Section I.A.12.a.

Verify Before Coding

• CC as a secondary diagnosis (FY2026). Can raise the stay's MS-DRG severity tier.

From the code registry, the Medicare Code Editor, and the MS-DRG Definitions Manual. Check it against a full claim in Claim Check.

Relationships & Classification

MedCoder structured relationships — computed from published CMS and AHRQ datasets

MS-DRG Grouper Relationships (FY2026)

Potential MS-DRG participation — not a DRG assignment.

FY2026 MS-DRG: CC — Complication or Comorbidity. Reported as a secondary diagnosis, this code raises the stay's MS-DRG severity tier — except when the principal diagnosis is one of 4 clinically related codes on its CMS exclusion list.

Named in the grouper logic of 2 MS-DRGs: DRG 922 (MDC 21), DRG 923 (MDC 21).

From the CMS MS-DRG Definitions Manual (Appendices B and C). Actual DRG assignment depends on the complete claim.

Clinical classification (AHRQ CCSR):INJ021 — Effect of other external causes, initial encounter (default).

Clinical Classifications Software Refined (CCSR) for ICD-10-CM Diagnoses. Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality.

Related Codes

Same clinical process (MS-DRG)

Acts as CC — raises the severity of other admissions. CMS groups these diagnoses into one MS-DRG principal-diagnosis exclusion process — a CC/MCC on this list never raises severity when the principal diagnosis is also on it.

T70.4XXA — Effects of high-pressure fluids, initial encounter, T70.8XXA — Other effects of air pressure and water pressure, initial encounter, T70.9XXA — Effect of air pressure and water pressure, unspecified, initial encounter

Same injury, other encounter phase

Same injury, coded at a different phase of treatment via the 7th character.

T70.3XXD — Caisson disease [decompression sickness], subsequent encounterCompare T70.3XXA vs T70.3XXD →, T70.3XXS — Caisson disease [decompression sickness], sequelaCompare T70.3XXA vs T70.3XXS →

Same clinical category (CCSR)

AHRQ's Clinical Classifications Software groups these diagnoses under the same clinical category (Effect of other external causes, initial encounter).

T69.021A — Immersion foot, right foot, initial encounter, T69.022A — Immersion foot, left foot, initial encounter, T69.029A — Immersion foot, unspecified foot, initial encounter, T69.1XXA — Chilblains, initial encounter, T69.8XXA — Other specified effects of reduced temperature, initial encounter, T69.9XXA — Effect of reduced temperature, unspecified, initial encounter, T70.0XXA — Otitic barotrauma, initial encounter, T70.1XXA — Sinus barotrauma, initial encounter, T70.20XA — Unspecified effects of high altitude, initial encounter, T70.29XA — Other effects of high altitude, initial encounter, T70.4XXA — Effects of high-pressure fluids, initial encounter, T70.8XXA — Other effects of air pressure and water pressure, initial encounter, T70.9XXA — Effect of air pressure and water pressure, unspecified, initial encounter, T71.111A — Asphyxiation due to smothering under pillow, accidental, initial encounter, T71.112A — Asphyxiation due to smothering under pillow, intentional self-harm, initial encounter, T71.113A — Asphyxiation due to smothering under pillow, assault, initial encounter, T71.114A — Asphyxiation due to smothering under pillow, undetermined, initial encounter, T71.121A — Asphyxiation due to plastic bag, accidental, initial encounter, T71.122A — Asphyxiation due to plastic bag, intentional self-harm, initial encounter, T71.123A — Asphyxiation due to plastic bag, assault, initial encounter, +149 more

Contextual Map

Every relationship of T70.3XXA in one view: hierarchy, official tabular instructions in both directions, clinical classification, risk adjustment, MS-DRG participation, index terms and change history — each edge carrying the CMS source it derives from.

Hierarchy

• S00-T88 — Chapter 19: Injury, Poisoning and Certain Other Consequences of External Causes (S00-T88) (S00-T88)[Hierarchy]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• T66-T78 — Other and unspecified effects of external causes[Hierarchy]— CMS ICD-10-CM tabular structure · icd10cm-fy2026

Clinical classification (CCSR)

• INJ021 — Effect of other external causes, initial encounter[CCSR]— AHRQ CCSR for ICD-10-CM Diagnoses (HCUP)

MS-DRG Grouper

• CC — Complication or Comorbidity [MS-DRG severity]: “As a secondary diagnosis this code can raise the stay's MS-DRG severity tier (CC).”— CMS MS-DRG Definitions Manual (Appendix C) · FY2026
• DRG 922 — OTHER INJURY, POISONING AND TOXIC EFFECT DIAGNOSES WITH MCC[MS-DRG]: “OTHER INJURY, POISONING AND TOXIC EFFECT DIAGNOSES WITH MCC (MDC 21)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2026
• DRG 923 — OTHER INJURY, POISONING AND TOXIC EFFECT DIAGNOSES WITHOUT MCC[MS-DRG]: “OTHER INJURY, POISONING AND TOXIC EFFECT DIAGNOSES WITHOUT MCC (MDC 21)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2026

MDC crossing

• MDC 21 — Injuries, Poisonings and Toxic Effects of Drugs[MDC crossing]: “Injuries, Poisonings and Toxic Effects of Drugs — the grouper's crossing between diagnoses and procedures: a principal diagnosis sets the MDC, and same-MDC procedures move the stay to its surgical DRGs. 32,029 same-MDC procedures group here; browse them on the MDC page.”— CMS MS-DRG Definitions Manual · FY2026

Nearest codes (33)

• T70 — Effects of air pressure and water pressure[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• T70.0 — Otitic barotrauma[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• T70.0XXA — Otitic barotrauma, initial encounter[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• T70.0XXD — Otitic barotrauma, subsequent encounter[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• T70.0XXS — Otitic barotrauma, sequela[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• T70.1 — Sinus barotrauma[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• T70.1XXA — Sinus barotrauma, initial encounter[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• T70.1XXD — Sinus barotrauma, subsequent encounter[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• and 25 more

Change history

• FY2016 — In the code set at ICD-10-CM adoption [Change history]— CMS release files (code change ledger) · icd10cm-fy2016

Common coding questions

Sources for this page

Codes, titles, notes, index terms and mappings on this page are transcribed from the datasets below. Relationships MedCoder computed and text MedCoder wrote are labelled where they appear.

Code, title, tabular notes and index terms Official source data

CMS/CDC ICD-10-CM FY2026 tabular list, index and tables, effective October 1, 2025 Release, file and checksum · Publisher’s page

Claim edits Official source data

CMS Definitions of Medicare Code Edits — v43.1 (April 2026) Release, file and checksum · Publisher’s page

Inpatient payment groups Official source data

CMS MS-DRG Definitions Manual (incl. Appendix B diagnosis index, Appendix C CC/MCC list, Appendix E procedure index) and IPPS Final Rule tables — v43 Release, file and checksum · Publisher’s page

Change history and date-of-service validity Official source data

CMS ICD-10-CM release addenda, ingested release by release into the change ledger Release, file and checksum · Publisher’s page

Comparisons, relationships and the contextual map MedCoder structured relationship

Computed by MedCoder from the tabular notes and tables above; every derived relationship is marked as derived where it appears

Summary and FAQ answers MedCoder explanation

Written by MedCoder to explain the sources above: drafted with AI assistance, checked by a person against the release files, and labelled as MedCoder text where it appears. Not official text.

Labels on this page: Official source data · MedCoder structured relationship · MedCoder explanation. How to read the labels · All data sources and release dates

Nearest Codes in This Family

Official ICD-10-CM classifications closest to T70.3XXA in its code family, with their registry titles.

• T70.29 — Other effects of high altitude
• T70.29XA — Other effects of high altitude, initial encounter
• T70.29XD — Other effects of high altitude, subsequent encounter
• T70.29XS — Other effects of high altitude, sequela
• T70.3 — Caisson disease [decompression sickness]
• T70.3XXD — Caisson disease [decompression sickness], subsequent encounter
• T70.3XXS — Caisson disease [decompression sickness], sequela
• T70.4 — Effects of high-pressure fluids
• T70.4XXA — Effects of high-pressure fluids, initial encounter
• T70.4XXD — Effects of high-pressure fluids, subsequent encounter

View all codes in the T70 family