2027 ICD-10-CM Diagnosis Code T65.822SToxic effect of harmful algae and algae toxins, intentional self-harm, sequela

ICD-10-CM Codes›S00–T88›T51-T65›T65

ICD-10-CM T65.822S
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

T65.822S is a billable ICD-10-CM diagnosis code for toxic effect of harmful algae and algae toxins, intentional self-harm, 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. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Mental and substance use disorders; sequela; and Poisoning/toxic effect/adverse effects/underdosing, sequela.

T65.822S no longer risk-adjusts for Medicare Advantage: it mapped to HCC 59 under the retired CMS-HCC V24 model through payment year 2025 but maps to no category in the live V28 model. It still risk-adjusts in the PACE (CMS-HCC V22) category 58, ESRD (V21) category 58, and ESRD (V24) category 59 for payment year 2027.

Code Identity

ICD-10-CM Code
T65.822S
Billable Status
Yes — Valid for Submission
Code Describes
Toxic effect of harmful algae and algae toxins, intentional self-harm, sequela
Short Description
Toxic eff of harmful algae and algae toxins, slf-hrm, sqla
Parent Code
T65.822
Toxic effect of harmful algae and algae toxins, intentional self-harm

Code Classification

ChapterS00–T88Injury, poisoning and certain other consequences of external causes
SectionT51-T65Toxic effects of substances chiefly nonmedicinal as to source
CategoryT65Toxic effect of other and unspecified substances
This CodeT65.822SToxic effect of harmful algae and algae toxins, intentional self-harm, sequela

Present on Admission (POA)Billing

T65.822S 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).

Medicare Risk Adjustment (HCC)Billing

T65.822S no longer risk-adjusts for Medicare Advantage: it maps to no payment category in the live CMS-HCC V28 model, although it still risk-adjusts in the other CMS models shown below.

CMS-HCC V28 (Medicare Advantage Payment Model)
Not mapped
Dropped in V28 see all codes that no longer risk-adjust
Prior Model (CMS-HCC V24)
HCC 59
V24 retired last contributed to a Medicare Advantage risk score in payment year 2025
Other CMS Models
PACE (CMS-HCC V22): HCC 58 · ESRD (V21): HCC 58 · ESRD (V24): HCC 59
ESRD V21 weights: 0.091 dialysis, 0.217–0.260 functioning graft · ESRD V24 weights: 0.066 dialysis, 0.129–0.259 functioning graft
Part D (RxHCC)
Not mapped
T65.822S does not risk-adjust in the RxHCC prescription drug model

Source: CMS Payment Year 2027 risk adjustment mappings and model software. Weights are relative factors, not dollar amounts; a beneficiary's total RAF also includes demographics and interactions. Browse all CMS-HCC categories.

Coding GuidelinesGuidance

The appropriate 7th character is to be added to each code from block Toxic effect of other and unspecified substances (T65). 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 T65.822S: its own notes plus those printed at T65, block T51-T65, and Chapter 19. A note printed at a category, block or chapter applies to every code under it.

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 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 T65 Toxic effect of other and unspecified substances applies to 192 codes
  • The appropriate 7th character is to be added to each code from category T65
Values for category T65 Encounter: Initial, Subsequent, Sequela
  • 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 T65.822S, its category, or a range that includes it.

Excludes1 2

These codes carry an Excludes1 note naming T65.822S: they are not reported together with it, unless the two conditions are unrelated.

  • T61 Toxic effect of noxious substances eaten as seafood
    toxic effect of harmful algae bloom (T65.82-) names T65.82-, which includes this code
  • T61 Toxic effect of noxious substances eaten as seafood
    toxic effect of red tide (T65.82-) names T65.82-, which includes this code

Clinical ClassificationClinical

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

CCSR MBD034
Mental and substance use disorders; sequela
Default principal diagnosis: inpatient Yes · outpatient Yes
CCSR INJ075
Poisoning/toxic effect/adverse effects/underdosing, sequela
Default principal diagnosis: inpatient No · outpatient No

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
Algae (harmful) (toxin)T65.821T65.822T65.823T65.824––

Convert T65.822S to ICD-9-CMHistory

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

ICD-9-CM
909.1 Late eff nonmed substanc
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
E959 Late eff of self-injury
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 T65.822SOverview

Is T65.822S a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report toxic effect of harmful algae and algae toxins, intentional self-harm, sequela on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What does the 7th character S in T65.822S mean?

The final character S makes this a sequela code: it reports a lingering problem that remains after the toxic effect of harmful algae and algae toxins, intentional self-harm itself has resolved, not the original event.

What MS-DRG does T65.822S group to?

When toxic effect of harmful algae and algae toxins, intentional self-harm, 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 T65.822S 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 harmful algae and algae toxins, intentional self-harm, 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.

Can T65.822S be reported with a code from Z77?

Not as a rule. The Excludes1 note at block T51-T65, which applies to T65.822S, 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).

Does T65.822S risk-adjust for Medicare Advantage payment?

Not for Medicare Advantage. T65.822S mapped to HCC 59 in the retired CMS-HCC V24 model, which last determined payment in 2025, but it maps to no category in the live V28 model; see all codes that no longer risk-adjust. It still risk-adjusts in the PACE (CMS-HCC V22) category 58 (Major Depressive/Bipolar/and Paranoid Disorders), ESRD (V21) category 58 (Major Depressive/Bipolar/and Paranoid Disorders), and ESRD (V24) category 59 (Major Depressive/Bipolar/and Paranoid Disorders).