2027 ICD-10-CM Diagnosis Code T63.331AToxic effect of venom of brown recluse spider, accidental (unintentional), initial encounter

ICD-10-CM Codes›S00–T88›T51-T65›T63

ICD-10-CM T63.331A
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

T63.331A is a billable ICD-10-CM diagnosis code for toxic effect of venom of brown recluse spider, accidental (unintentional), initial encounter. The 7th character A marks it as an initial encounter code, used while the patient is receiving active treatment. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 917 through 918. Coders also document this condition as poisoning due to bite of brown recluse spider. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under External cause codes: bites; initial encounter; External cause codes: intent of injury, accidental/unintentional; and Toxic effects, initial encounter.

Code Identity

ICD-10-CM Code
T63.331A
Billable Status
Yes — Valid for Submission
Code Describes
Toxic effect of venom of brown recluse spider, accidental (unintentional), initial encounter
Short Description
Toxic effect of venom of brown recluse spider, acc, init
Parent Code
T63.331
Toxic effect of venom of brown recluse spider, accidental (unintentional)

Code Classification

ChapterS00–T88Injury, poisoning and certain other consequences of external causes
SectionT51-T65Toxic effects of substances chiefly nonmedicinal as to source
CategoryT63Toxic effect of contact with venomous animals and plants
This CodeT63.331AToxic effect of venom of brown recluse spider, accidental (unintentional), initial encounter

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Poisoning due to bite of brown recluse spider
  • Poisoning due to bite of venomous spider
  • Spider bite wound

Coding GuidelinesGuidance

The appropriate 7th character is to be added to each code from block Toxic effect of contact with venomous animals and plants (T63). 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 T63.331A: its own notes plus those printed at T63, 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.

From T63 Toxic effect of contact with venomous animals and plants applies to 456 codes
  • bite or touch of venomous animal
  • pricked or stuck by thorn or leaf

Excludes1

Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.

From Block T51-T65 Toxic effects of substances chiefly nonmedicinal as to source applies to 1,680 codes
  • 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.

From T63 Toxic effect of contact with venomous animals and plants applies to 456 codes
From Chapter 19 (S00-T88) Injury, poisoning and certain other consequences of external causes applies to 41,187 codes

Use Additional Code

Add a second code, after this one, to fully describe the condition.

From Block T51-T65 Toxic effects of substances chiefly nonmedicinal as to source applies to 1,680 codes
  • code(s):
  • for all associated manifestations of toxic effect, such as: respiratory conditions due to external agents (J60-J70)
  • personal history of foreign body fully removed (Z87.821)
  • to identify any retained foreign body, if applicable (Z18.-)
From Chapter 19 (S00-T88) Injury, poisoning and certain other consequences of external causes applies to 41,187 codes
  • code to identify any retained foreign body, if applicable (Z18.-)

Notes

General instructions on how these codes are used.

From Block T51-T65 Toxic effects of substances chiefly nonmedicinal as to source applies to 1,680 codes
  • 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.
From Chapter 19 (S00-T88) Injury, poisoning and certain other consequences of external causes applies to 41,187 codes
  • 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.

From T63 Toxic effect of contact with venomous animals and plants applies to 456 codes
  • The appropriate 7th character is to be added to each code from category T63
Values for category T63 Encounter: Initial, Subsequent, Sequela
  • Ainitial encounter this code
  • Dsubsequent encounter
  • Ssequela

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name T63.331A, its category, or a range that includes it.

Excludes1 4

These codes carry an Excludes1 note naming T63.331A: they are not reported together with it, unless the two conditions are unrelated.

  • Block W50-W64 Exposure to animate mechanical forces
    Toxic effect of contact with venomous animals and plants (T63.-) names T63.-, which includes this code
  • W56 Contact with nonvenomous marine animal
    contact with venomous marine animal (T63.-) names T63.-, which includes this code
  • W57 Bitten or stung by nonvenomous insect and other nonvenomous arthropods
    contact with venomous insects and arthropods (T63.2-, T63.3-, T63.4-) names T63.3-, which includes this code
  • W64 Exposure to other animate mechanical forces
    contact with venomous animal (T63.-) names T63.-, which includes this code

Excludes2 1

These codes carry an Excludes2 note naming T63.331A: its condition is not part of those codes, and both may be reported when the patient has both.

  • S71 Open wound of hip and thigh
    bite of venomous animal (T63.-) names T63.-, which includes this code

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR EXT012
External cause codes: bites; initial encounter
Default principal diagnosis: inpatient No · outpatient No
CCSR EXT020
External cause codes: intent of injury, accidental/unintentional
Default principal diagnosis: inpatient No · outpatient No
CCSR INJ023
Toxic effects, initial encounter
Default principal diagnosis: inpatient Yes · outpatient Yes

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.

SubstanceAccidentalSelf-harmAssaultUndeter­minedAdverse
Effect		Under­dosing
Brown recluse spider (bite) (venom)T63.331T63.332T63.333T63.334––
Venom, venomous (bite) (sting)::spider::brown recluseT63.331T63.332T63.333T63.334––

Patient EducationClinical

Spider Bites

Though many people are afraid of spiders, they rarely bite people unless threatened. Most spider bites are harmless. Occasionally, spider bites can cause allergic reactions. And bites by the venomous black widow and brown recluse spiders can be very dangerous to people.

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert T63.331A to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
989.5 Toxic effect venom
ApproximateCombination The match is approximate, and more than one code can be needed to describe the source diagnosis. Confirm with contextual judgment.
ICD-9-CM
E905.1 Venomous spider bite
ApproximateCombination The match is approximate, and more than one code can be needed to describe the source diagnosis. Confirm with contextual judgment.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About T63.331AOverview

Is T63.331A a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report toxic effect of venom of brown recluse spider, accidental (unintentional), initial encounter on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What does the 7th character A in T63.331A mean?

The final character A marks the initial encounter: use it while the patient is receiving active treatment for toxic effect of venom of brown recluse spider, accidental (unintentional), such as an emergency visit or first evaluation.

What MS-DRG does T63.331A group to?

When toxic effect of venom of brown recluse spider, accidental (unintentional), initial encounter is the principal diagnosis on an inpatient stay, it groups to MS-DRG 918, 917, with relative weights from 0.8716 to 1.5698 depending on complications. Higher weights mean higher Medicare reimbursement.

Can T63.331A be reported with a code from Z77?

Not as a rule. The Excludes1 note at block T51-T65, which applies to T63.331A, lists "contact with and (suspected) exposure to toxic substances (Z77.-)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).

What is the ICD-9 equivalent of T63.331A?

Under the General Equivalence Mappings, toxic effect of venom of brown recluse spider, accidental (unintentional), initial encounter converts to ICD-9-CM 989.5 (toxic effect venom) and E905.1 (venomous spider bite). The mapping is approximate, so confirm the match fits the documentation.