X31 ICD-10-CM Code: Exposure to excessive natural cold

Coding instructions

Official Tabular Instructional Notes: the inclusion, exclusion and sequencing notes published for X31 in the official ICD-10-CM tabular list, quoted as published.

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

7th Character Guide

"The appropriate 7th character is to be added to code X31"

• A — initial encounter
• 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

X31.XXXA, X31.XXXD, X31.XXXS

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 X31

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

Before you code X31

1. X31 is not reportable as written. Select the more specific code beneath it that the documentation supports. Codes are reported to the highest level of specificity the classification provides (Guidelines I.B.2).

   ReviewX31.XXXA, X31.XXXD, X31.XXXS

   See the relationships section · Guide: How to choose an ICD-10-CM code →

2. A 7th character is required in this family. Confirm the documented encounter: initial (active treatment), subsequent (healing or recovery phase), or sequela. X31 is not valid without one. “Initial” means active treatment, not the first visit (Guidelines I.C.19.a).

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

3. An external cause code is reported in addition to the code for the injury or condition, never as the principal or first-listed diagnosis. Confirm the cause, intent, place of occurrence, activity and status where the record documents them, and assign the 7th character that matches the injury code. External cause coding guidelines (Guidelines I.C.20.a).

4. Check the Excludes1 note: if the documentation supports a condition named there, do not simply proceed with X31. Excludes1 conditions are not reported together with this code unless the record shows they are unrelated (Guidelines I.A.12.a).

   See the official tabular notes

Choose the right path

1. Does the documentation support one of the more specific codes beneath X31?
   Yes → Select that code and continue the checks below on its own page.
   No → X31 cannot be reported as written; query for the specificity its subcategory needs.

   ReviewX31.XXXA, X31.XXXD, X31.XXXS

2. Does the documentation support a condition named in X31’s Excludes1 note?
   Yes → Do not simply proceed: review the excluded code. Both are reported only when the record shows the two conditions are unrelated.
   No → Continue.

   ReviewW93

3. 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 X31. Then 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

• Excludes1 — check before selecting X31(3 notes)

  Coding workflow: If the documentation supports a condition named in this note, do not simply proceed with X31: the two are not reported together. The one exception is when the record shows the two conditions are unrelated to each other.

  CompareW93

  See the official tabular notes · Guidelines I.A.12.a

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.

Indexed As (6)

Official source data — entries quoted as published, in the Index’s own lookup phrasing

Circumstance phrases from the official ICD-10-CM External Cause of Injuries Index that map to this code.

• Exposure (to), cold (accidental) (excessive) (extreme) (natural) (place)
• Exposure (to), cold (accidental) (excessive) (extreme) (natural) (place), due to, weather (conditions)
• Forces of nature, cold (natural)
• Frostbite
• Immersion (accidental), hand or foot due to cold (excessive)
• Overexposure (accidental) (to), cold

Don’t confuse X31 with…

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

The codes most likely to be picked instead of X31 — 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.

• W93— Excludes1 conflict (Excludes1 — generally not reported together)

  Not coded here — the tabular list excludes this pair for the same encounter.

  Not reported together with this code, except where the two conditions are documented as unrelated.

  What moves you there: Documentation of cold of man-made origin moves the case to W93; the two are not reported together unless documented as unrelated.

  Full comparison: X31 vs W93 →

• X31.XXXA— 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 initial encounter moves the case to X31.XXXA.

  Full comparison: X31 vs X31.XXXA →

• X31.XXXD— 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 X31.XXXD.

  Full comparison: X31 vs X31.XXXD →

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

• Not billable as written — a more specific code is required: X31.XXXA, X31.XXXD, X31.XXXS.
• Requires a 7th character. "The appropriate 7th character is to be added to code X31" Options: X31.XXXA, X31.XXXD, X31.XXXS
• Principal-diagnosis restriction. External cause of morbidity codes (V, W, X and Y) describe the circumstance that caused an injury, not the condition treated. The Medicare Code Editor rejects them as a principal diagnosis; sequence the injury or condition first and report this code as secondary.

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

Other codes that name X31 or its code family, from the CMS ICD-10-CM tabular instructional notes. Tabular-note edges are stored at the code family level that carries each note.

Referenced by 10 Excludes1 notes: W85 — Exposure to electric transmission lines, W85-W99 — Exposure to electric current, radiation and extreme ambient air temperature and pressure (W85-W99), W86 — Exposure to other specified electric current, W88 — Exposure to ionizing radiation, W89 — Exposure to man-made visible and ultraviolet light, W90 — Exposure to other nonionizing radiation, W92 — Exposure to excessive heat of man-made origin, W93 — Exposure to excessive cold of man-made origin, W94 — Exposure to high and low air pressure and changes in air pressure, W99 — Exposure to other man-made environmental factors.

These codes’ tabular lists mark this diagnosis as mutually exclusive — not reported together unless the conditions are documented as unrelated.

Referenced by 2 Use Additional Code instructions: T68 — Hypothermia, T69 — Other effects of reduced temperature.

These codes instruct coders to additionally report this code when it applies.

Contextual Map

Every relationship of X31 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.

Run X31 with these 10 related codes in Claim Check

Hierarchy

• V00-Y99 — Chapter 20: External Causes of Morbidity (V00-Y99) (V00-Y99)[Hierarchy]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• W00-X58 — Other external causes of accidental injury[Hierarchy]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• X30-X39 — Exposure to forces of nature[Hierarchy]— CMS ICD-10-CM tabular structure · icd10cm-fy2026

Excludes1

• W93 — Exposure to excessive cold of man-made origin[Excludes1]: “cold of man-made origin (W93.-)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026

Referenced by Excludes1 notes (10)

• W85 — Exposure to electric transmission lines[Excludes1]: “natural cold (X31)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026
• W85-W99 — Exposure to electric current, radiation and extreme ambient air temperature and pressure (W85-W99)[Excludes1]: “natural cold (X31)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026
• W86 — Exposure to other specified electric current[Excludes1]: “natural cold (X31)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026
• W88 — Exposure to ionizing radiation[Excludes1]: “natural cold (X31)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026
• W89 — Exposure to man-made visible and ultraviolet light[Excludes1]: “natural cold (X31)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026
• W90 — Exposure to other nonionizing radiation[Excludes1]: “natural cold (X31)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026
• W92 — Exposure to excessive heat of man-made origin[Excludes1]: “natural cold (X31)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026
• W93 — Exposure to excessive cold of man-made origin[Excludes1]: “natural cold (X31)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026
• and 2 more

Referenced by Use Additional Code instructions

• T68 — Hypothermia[Use Additional Code]: “Exposure to excessive cold of natural origin (X31)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026
• T69 — Other effects of reduced temperature[Use Additional Code]: “Exposure to excessive cold of natural origin (X31)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026

External cause index

• Exposure (to), cold (accidental) (excessive) (extreme) (natural) (place)[External cause term]— CMS External Cause of Injuries Index · icd10cm-fy2026
• Exposure (to), cold (accidental) (excessive) (extreme) (natural) (place), due to, weather (conditions)[External cause term]— CMS External Cause of Injuries Index · icd10cm-fy2026
• Forces of nature, cold (natural)[External cause term]— CMS External Cause of Injuries Index · icd10cm-fy2026
• Frostbite[External cause term]— CMS External Cause of Injuries Index · icd10cm-fy2026
• Immersion (accidental), hand or foot due to cold (excessive)[External cause term]— CMS External Cause of Injuries Index · icd10cm-fy2026
• Overexposure (accidental) (to), cold[External cause term]— CMS External Cause of Injuries Index · icd10cm-fy2026

Nearest codes

• X31.XXXA — Exposure to excessive natural cold, initial encounter[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• X31.XXXD — Exposure to excessive natural cold, subsequent encounter[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• X31.XXXS — Exposure to excessive natural cold, sequela[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026

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

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 X31 in its code family, with their registry titles.

• X31.XXXA — Exposure to excessive natural cold, initial encounter
• X31.XXXD — Exposure to excessive natural cold, subsequent encounter
• X31.XXXS — Exposure to excessive natural cold, sequela