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G90.81 ICD-10-CM Code: Serotonin syndrome

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

Coding at a Glance

Tabular directives
1 inclusion term · 1 Excludes1 · 12 use-additional codes · 5 code-first instructions

Inpatient Payment Groups (MS-DRG)

Potential MS-DRG participation — not a DRG assignment.

MS-DRGs this diagnosis helps define, as principal or secondary, per the CMS ICD-10-CM/PCS MS-DRG Definitions Manual v44, Appendix B.

  • MS-DRG 073 — CRANIAL AND PERIPHERAL NERVE DISORDERS WITH MCC (MDC 01)
  • MS-DRG 074 — CRANIAL AND PERIPHERAL NERVE DISORDERS WITHOUT MCC (MDC 01)

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.

Coding instructions

Official Tabular Instructional Notes: the inclusion, exclusion and sequencing notes published for G90.81 in the official ICD-10-CM tabular list, quoted as published.

Source: CMS/CDC — ICD-10-CM Tabular ListRelease: FY2027Effective: October 1, 2026

Trace:FY2027 changesChange historyRelease, file and checksum

Notes without a marker are published on G90.81 itself; “inherited from” names the category or block whose note applies here.

Inclusion Terms

Alternative terms the tabular list files under this code.

  • Serotonin toxicity

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).

Source: inherited from G90

Code First

Underlying conditions that must be sequenced before this code.

  • poisoning due to drug or toxin, such as:
  • linezolid (T36.8X- with sixth character 1-4)
  • monoamine oxidase inhibitors (T43.1X with sixth character 1-4)
  • selective serotonin and norepinephrine reuptake inhibitors SSNRI
  • selective serotonin reuptake inhibitors SSRI

Use Additional Code

Supplementary codes the tabular list directs you to add.

  • Use additional code for adverse effect, if applicable, to identify drug, such as:
  • linezolid (T36.8X5)
  • monoamine oxidase inhibitors (T43.1X5)
  • selective serotonin and norepinephrine reuptake inhibitors SSNRI
  • selective serotonin reuptake inhibitors SSRI
  • Use additional code, if applicable, to identify:
  • disseminated intravascular coagulation (D65)
  • hypertensive crisis (I16.-)
  • metabolic acidosis (E87.2-)
  • shock, not elsewhere classified (R57.-)
  • toxic encephalopathy (G92.-)
  • ventricular tachycardia (I47.2-)

Coder workflow for G90.81

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

Before you code G90.81

  1. Check the Excludes1 note: if the documentation supports a condition named there, do not simply proceed with G90.81. 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 a condition named in G90.81’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.

    ReviewG31.2

  2. Is the underlying (etiologic) condition the Code First note names documented?
    Yes → Sequence the underlying condition first, then G90.81.
    No → Continue; do not add an underlying condition the record does not document.

    ReviewT36.8X, T43.1X

Consider G90.81. Then work the Use Additional Code 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).
The underlying (etiologic) condition
Named in the Code First note; sequenced before this code when documented (Guidelines I.A.13).
The conditions the Use Additional Code note names
Reported with this code when documented; a conditional instruction (“if applicable”, “if known”) applies only when the record supports it.

Official instructions as workflow

  • Excludes1 — check before selecting G90.81(1 note)

    Coding workflow: If the documentation supports a condition named in this note, do not simply proceed with G90.81: the two are not reported together. The one exception is when the record shows the two conditions are unrelated to each other.

    CompareG31.2

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

  • Code First — sequencing check(5 notes)

    Coding workflow: Check whether the underlying or etiologic condition the note names is documented. When it is, sequence it before G90.81. Do not add an underlying condition the record does not document.

    ReviewT36.8X, T43.1X

    See the official tabular notes · Guidelines I.A.13

  • Use Additional Code — after identifying G90.81(12 notes)

    Coding workflow: Check whether the documentation supports the additional code(s) the note names, and report them with G90.81 when it does. Where the instruction is conditional (“if applicable”, “if known”), it applies only when the record documents the condition.

    ReviewT36.8X5, T43.1X5, D65, I16, E87.2, R57

    See the official tabular notes · Guidelines I.A.13

Coding decision scenarios

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

Documentation: Both the condition G90.81 describes and a condition named in its Excludes1 note are documented for the same encounter.

Coding question: Can both codes be reported?

Path: Review the Excludes1 note and the excluded code, and look for a provider statement on whether the two conditions are related.

Reason: Excludes1 means the two are not coded together; the exception is when the record shows the conditions are unrelated to each other (Guidelines I.A.12.a).

ReviewG31.2

Documentation: The underlying condition the Code First note names is documented alongside this condition.

Coding question: How are the two sequenced?

Path: Review the Code First note.

Reason: The underlying condition is sequenced first and the manifestation follows (Guidelines I.A.13).

ReviewT36.8X, T43.1X

Documentation: A condition the Use Additional Code note names is documented.

Coding question: Is a second code reported with G90.81?

Path: Review the Use Additional Code note and the code it names.

Reason: The additional code is reported when the record documents the condition; a conditional instruction applies only when its condition is met (Guidelines I.A.13).

ReviewT36.8X5, T43.1X5, D65, I16, E87.2, R57

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 G90.81 with…

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

The codes most likely to be picked instead of G90.81 — 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.

  • G31.2— 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 dysfunction of the autonomic nervous system due to alcohol moves the case to G31.2; the two are not reported together unless documented as unrelated.

    Full comparison: G90.81 vs G31.2 →

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.

Code Overview

Serotonin syndrome is a billable ICD-10-CM diagnosis code (G90.81).

MedCoder summary Summary composed by MedCoder from this code's official ICD-10-CM record. The tabular instructional notes themselves appear verbatim below.

Indexed Clinical Terms (1)

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

Clinical term phrases from the official ICD-10-CM Index to Diseases and Injuries that map to this code. These are alphabetic-index entries shown as the Index writes them — lookup phrasing, not necessarily the wording of a final diagnosis.

Decision Points

The directives on this code's own record, as a pre-claim checklist.

  1. Sequencing: 5 Code First instructions — the underlying condition is sequenced before this code when present. See the Code First notes
  2. 12 Use Additional Code instructions — report the named additional code(s) when the documentation supports them. See the Use Additional Code notes
  3. 1 Excludes1 entry — codes named there are generally not reported together with this code (Guidelines I.A.12.a). See the Excludes1 notes

Checklist rows are derived from this code's own official directives; the wording of each check is MedCoder editorial. The official notes themselves are in the sections each row links to.

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 in Claim Check.

Relationships & Classification

MedCoder structured relationships — computed from published CMS and AHRQ datasets

MS-DRG Grouper Relationships (FY2027)

Potential MS-DRG participation — not a DRG assignment.

FY2027 MS-DRG: not on the CMS CC/MCC list — as a secondary diagnosis this code does not change MS-DRG severity for that release.

Named in the grouper logic of 2 MS-DRGs: DRG 073 (MDC 01), DRG 074 (MDC 01).

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

Clinical classification (AHRQ CCSR):NVS020 — Other nervous system disorders (neither hereditary nor degenerative) (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 category (CCSR)

AHRQ's Clinical Classifications Software groups these diagnoses under the same clinical category (Other nervous system disorders (neither hereditary nor degenerative)).

G46.1 — Anterior cerebral artery syndrome, G46.2 — Posterior cerebral artery syndrome, G46.3 — Brain stem stroke syndrome, G46.4 — Cerebellar stroke syndrome, G46.5 — Pure motor lacunar syndrome, G46.6 — Pure sensory lacunar syndrome, G46.7 — Other lacunar syndromes, G46.8 — Other vascular syndromes of brain in cerebrovascular diseases, G64 — Other disorders of peripheral nervous system, G90.8 — Other disorders of autonomic nervous system, G90.89 — Other disorders of autonomic nervous system, G90.9 — Disorder of the autonomic nervous system, unspecified, G90.A — Postural orthostatic tachycardia syndrome [POTS], G91.0 — Communicating hydrocephalus, G91.1 — Obstructive hydrocephalus, G91.2 — (Idiopathic) normal pressure hydrocephalus, G91.3 — Post-traumatic hydrocephalus, unspecified, G91.4 — Hydrocephalus in diseases classified elsewhere, G91.8 — Other hydrocephalus, G91.9 — Hydrocephalus, unspecified, +97 more

Lab tests where this diagnosis supports Medicare coverage (NCD)

Medicare's National Coverage Determination (NCD) program lists this diagnosis as medical justification for these lab tests.

Blood Glucose Test

Contextual Map

Every relationship of G90.81 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 G90.81 with these 12 related codes in Claim Check

Hierarchy

Code First

Use Additional Code (10)

Clinical classification (CCSR)

MS-DRG Grouper

MDC crossing

  • MDC 01 — Diseases and Disorders of the Nervous System[MDC crossing]: “Diseases and Disorders of the Nervous System — 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. 8,919 same-MDC procedures group here; browse them on the MDC page.”— CMS MS-DRG Definitions Manual · FY2027

Index entries

  • Syndrome, serotonin[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2027

Nearest codes (26)

Change history

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 FY2027 tabular list, index and tables, effective October 1, 2026 Release, file and checksum · Publisher’s page
Claim edits Official source data
CMS Definitions of Medicare Code Edits — v44.0 (October 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 — v44 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

Cite this page

Reference this page in a research guide, syllabus or article. The release is included because code content changes each year.

MedCoder.ai. "G90.81 — Serotonin syndrome." ICD-10-CM FY2027. https://medcoder.ai/icd10/code/g90.81-serotonin-syndrome

Change history

  • FY2025 — October 1, 2024
    Added to the code set
    Serotonin syndrome
    FY2025 changes

Nearest Codes in This Family

Official ICD-10-CM classifications closest to G90.81 in its code family, with their registry titles.

View all codes in the G90 family