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T78.41XA ICD-10-CM Code: Arthus phenomenon, initial encounter

Billing Status: YES. This is a valid, specific, and billable ICD-10-CM reference.

Inpatient Payment Groups (MS-DRG)

MS-DRGs this diagnosis helps define, as principal or secondary, per the CMS ICD-10-CM/PCS MS-DRG Definitions Manual v43.0, Appendix B.

  • MS-DRG 791 — PREMATURITY WITH MAJOR PROBLEMS (MDC 15)
  • MS-DRG 793 — FULL TERM NEONATE WITH MAJOR PROBLEMS (MDC 15)
  • MS-DRG 917 — POISONING AND TOXIC EFFECTS OF DRUGS WITH MCC (MDC 21)
  • MS-DRG 918 — POISONING AND TOXIC EFFECTS OF DRUGS WITHOUT MCC (MDC 21)

A diagnosis appearing in a group's logic does not by itself determine the DRG assigned to a stay; the grouper uses the full claim.

Official Registry Overview & Definition

Arthus phenomenon, initial encounter is a billable ICD-10-CM diagnosis code (T78.41A).

Official Tabular Instructional Notes

Sequencing, inclusion, and exclusion notes published for T78.41XA in the official ICD-10-CM tabular list.

Inclusion Terms

Alternative terms the tabular list files under this code.

  • Arthus reaction

Excludes1 — Not Coded Here

Conditions generally not reported together with this code (Excludes1) -- an error unless the two conditions are documented as unrelated to each other (ICD-10-CM Official Guidelines, Section I.A.12.a).

Excludes2 — Not Included Here

Conditions not covered by this code, but which may be reported alongside it when both are present.

Code Also

Additional codes that may be required to fully describe the encounter.

  • Code also, if applicable, place of occurrence, such as:
  • highway rest stop (Y92.523)
  • school (private) (public) (state) as the place of occurrence of the external cause (Y92.21-)
  • service areas as the place of occurrence of the external cause (Y92.52-)
  • single-family non-institutional (private) house as the place of occurrence of the external cause (Y92.01-)
  • transport vehicle as the place of occurrence of the external cause (Y92.81-)

Frequently Compared Codes

The official Excludes notes on T78.41XA name these codes. Each comparison page covers when the two can — or must not — be reported together.

Change history

No changes recorded for this code — unchanged since the FY2016 baseline of the change ledger.

Verify Before Coding

  • No Medicare Code Editor or MS-DRG Definitions Manual restrictions apply to this code.

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

Relationships & Classification

Official ICD-10-CM tabular notes on other codes that name T78.41XA or its code family.

1 Excludes1 notes: T75 (via T78.-).

Potential MS-DRG Relationships (FY2026)

Not on the CMS CC/MCC list — as a secondary diagnosis this code does not change MS-DRG severity.

Named in the grouper logic of 4 MS-DRGs: DRG 791 (MDC 15), DRG 793 (MDC 15), DRG 917 (MDC 21), DRG 918 (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):INJ031 — Allergic reactions (default).

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

Contextual Map

Every relationship of T78.41XA 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]
  • T66-T78 — Other and unspecified effects of external causes [Hierarchy]

Referenced by Excludes1 notes

  • T75 — Other and unspecified effects of other external causes [Excludes1](via T78.-): “adverse effects NEC (T78.-)” · check together

Clinical classification (CCSR)

  • INJ031 — Allergic reactions [CCSR]

Potential MS-DRG

  • DRG 791 — PREMATURITY WITH MAJOR PROBLEMS [MS-DRG]: “PREMATURITY WITH MAJOR PROBLEMS (MDC 15)”
  • DRG 793 — FULL TERM NEONATE WITH MAJOR PROBLEMS [MS-DRG]: “FULL TERM NEONATE WITH MAJOR PROBLEMS (MDC 15)”
  • DRG 917 — POISONING AND TOXIC EFFECTS OF DRUGS WITH MCC [MS-DRG]: “POISONING AND TOXIC EFFECTS OF DRUGS WITH MCC (MDC 21)”
  • DRG 918 — POISONING AND TOXIC EFFECTS OF DRUGS WITHOUT MCC [MS-DRG]: “POISONING AND TOXIC EFFECTS OF DRUGS WITHOUT MCC (MDC 21)”

MDC crossing · procedures (32029)

  • MDC 15 — Newborns and Other Neonates with Conditions Originating in Perinatal Period [MDC crossing]: “Newborns and Other Neonates with Conditions Originating in Perinatal Period — 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.”
  • 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.”
  • and 32029 more

Nearest codes (40)

  • T78 — Adverse effects, not elsewhere classified [Sibling]
  • T78.120 — Other adverse food reaction due to egg with tolerance to baked egg [Sibling]
  • T78.120A — Other adverse food reaction due to egg with tolerance to baked egg, initial encounter [Sibling]
  • T78.120D — Other adverse food reaction due to egg with tolerance to baked egg, subsequent encounter [Sibling]
  • T78.120S — Other adverse food reaction due to egg with tolerance to baked egg, sequela [Sibling]
  • T78.121 — Other adverse food reaction due to egg with reactivity to baked egg [Sibling]
  • T78.121A — Other adverse food reaction due to egg with reactivity to baked egg, initial encounter [Sibling]
  • T78.121D — Other adverse food reaction due to egg with reactivity to baked egg, subsequent encounter [Sibling]
  • and 32 more

Frequently Asked Questions (FAQ) & Clinical Guidance

Does T78.41XA require a 7th character?

Yes. The appropriate 7th character is to be added to each code from category T78.

Nearest Codes in This Family

Official ICD-10-CM classifications closest to T78.41XA in its code family, with their registry titles.

  • T78.40 — Allergy, unspecified
  • T78.40XA — Allergy, unspecified, initial encounter
  • T78.40XD — Allergy, unspecified, subsequent encounter
  • T78.40XS — Allergy, unspecified, sequela
  • T78.41 — Arthus phenomenon
  • T78.41XD — Arthus phenomenon, subsequent encounter
  • T78.41XS — Arthus phenomenon, sequela
  • T78.49 — Other allergy
  • T78.49XA — Other allergy, initial encounter
  • T78.49XD — Other allergy, subsequent encounter

View all codes in the T78 family