Crystal's MCW Coder Hub🧠 ICD-10-CM I63.231 — Cerebral Infarction, Right Carotid Artery, Unspecified Mechanism
Billable Code Confirmed — 6 Characters Complete
# ICD-10 CM I63.231 is a valid, billable 6-character ICD-10-CM code for FY2025. Structure:
I63(cerebral infarction) +.2(unspecified occlusion or stenosis, precerebral arteries) +3(carotid artery) +1(right side). No additional characters required — this code is complete.
Non-Billable Parent Codes — Do Not Submit
- ❌
I63.23— 5-character — non-billable header — missing laterality- ❌
I63.2— 4-character — non-billable header — missing artery and laterality- ❌
I63— 3-character — category only — never billable
🔴 CDI Alert — "Unspecified" Mechanism Is a Query Trigger
The
.2in this code means the occlusion or stenosis mechanism is unspecified — the record does not state whether the carotid artery occlusion was caused by thrombosis (clot formed in place) or embolism (clot traveled from another location). This distinction has direct implications for clinical accuracy, DRG grouping, and quality reporting. Send a CDI query to determine if a more specific code is supported.
🔍 Code Description
# ICD-10 CM I63.231 classifies acute cerebral infarction (ischemic stroke) caused by unspecified occlusion or stenosis of the right carotid artery — a precerebral (extracranial) vessel supplying the right cerebral hemisphere and right eye. The right internal carotid artery (ICA) provides the majority of blood flow to the right frontal, parietal, and temporal lobes via the right middle cerebral artery (MCA) and right anterior cerebral artery (ACA), and to the right eye via the right ophthalmic artery.
The word “unspecified” in this code is critical: it signals that the medical record does not clearly document whether the occlusion mechanism was thrombosis (atherosclerotic plaque rupture causing in-situ clot) or embolism (clot originating elsewhere — most commonly the heart in atrial fibrillation, or the carotid plaque itself). This ambiguity is almost always resolvable through clinical workup documentation — atrial fibrillation workup, echocardiogram, carotid imaging — making I63.231 a high-priority CDI code that should rarely remain “unspecified” when the full workup is available.
🌳 Code Tree / Hierarchy — Right Carotid Stroke by Mechanism
I63 Cerebral Infarction ❌ Non-billable category
│
├── I63.0 Thrombosis of precerebral arteries
│ └── I63.03 Carotid artery
│ └── I63.031 RIGHT carotid artery — THROMBOSIS ✅
│ (atherosclerotic plaque → in-situ clot)
│
├── I63.1 Embolism of precerebral arteries
│ └── I63.13 Carotid artery
│ └── I63.131 RIGHT carotid artery — EMBOLISM ✅
│ (cardiac embolus, artery-to-artery embolus)
│
└── I63.2 UNSPECIFIED occlusion/stenosis precerebral ❌ Non-billable
└── I63.23 Carotid artery ❌ Non-billable header
├── I63.231 RIGHT carotid ← THIS CODE ✅ ⚠️ Query mechanism
├── I63.232 Left carotid
├── I63.233 Bilateral carotid
└── I63.239 Unspecified carotid
📊 Mechanism Matters — The CDI Query Decision
| Mechanism | Code | When Documented | Key Clinical Clue |
|---|---|---|---|
| Thrombosis | I63.031 | Atherosclerotic stenosis, plaque rupture, in-situ clot, no cardiac source | Severe carotid stenosis (>50%) on CTA/MRA; no AFib; no cardioembolic source |
| Embolism | I63.131 | AFib, endocarditis, cardiomyopathy, artery-to-artery embolus | AFib on EKG/telemetry; low EF on echo; cardioembolic pattern on MRI (multiple territory) |
| Unspecified ← This Code | I63.231 | Mechanism not documented despite workup | Workup inconclusive OR mechanism not addressed in record |
Artery-to-Artery Embolism = Embolism Code (I63.131)
A common documentation and coding nuance: when a carotid plaque sends a fragment downstream to the cerebral vessels, this is artery-to-artery embolism — coded as I63.131 (embolism), NOT I63.031 (thrombosis) or I63.231 (unspecified). The source of the clot is the carotid plaque, but the mechanism is still embolic. If the neurologist documents “carotid artery-to-artery embolism” → I63.131 is correct.
CDI Query Template — Stroke Mechanism Specification
CLINICAL DOCUMENTATION IMPROVEMENT QUERY
Date: _
Patient: _ MRN: _
Encounter: _
RE: Cerebral Infarction — Right Carotid Artery — Mechanism Clarification
The medical record documents acute cerebral infarction involving
the right carotid artery. To assign the most specific ICD-10-CM
code, please clarify the etiology of the right carotid occlusion:
□ Thrombosis — in-situ clot at atherosclerotic plaque site
(Code I63.031 — thrombosis of right carotid artery)
□ Embolism — clot originated elsewhere (heart, proximal artery)
and traveled to the right carotid/cerebral territory
(Code I63.131 — embolism of right carotid artery)
□ Unspecified — mechanism cannot be determined from workup
(Code I63.231 — unspecified occlusion/stenosis remains)
Physician Signature: _ Date: _
📋 Clinical Overview — Right Carotid Territory Stroke
Anatomy — Why the Right Carotid?
The right common carotid artery (CCA) bifurcates in the neck into:
- Right external carotid artery (ECA) — supplies face, scalp, dura
- Right internal carotid artery (ICA) — enters skull → supplies right hemisphere and right eye
Right ICA branches (intracranially):
- Right ophthalmic artery → right eye (ipsilateral)
- Right anterior choroidal artery → internal capsule, basal ganglia
- Right MCA → right lateral hemisphere (frontal, parietal, temporal)
- Right ACA → right medial hemisphere (frontal, parietal)
Important
Atherosclerotic plaque most commonly forms at the carotid bifurcation in the neck — the junction of the CCA with the ICA and ECA. This is the precise location visualized on carotid duplex ultrasound and CTA of the neck.
Clinical Presentation — Right Carotid Stroke
| Symptom | Laterality | Explanation |
|---|---|---|
| Left-sided weakness or hemiplegia | Contralateral | Right hemisphere → crosses to left motor pathway |
| Left-sided sensory loss | Contralateral | Right somatosensory cortex processes left body |
| Left homonymous hemianopia | Contralateral visual field | Right optic radiation; right occipital lobe |
| Right eye amaurosis fugax | IPSILATERAL | Right ophthalmic artery occlusion → right eye |
| Left hemispatial neglect | Contralateral | Right parietal lobe — non-dominant hemispatial processing |
| Visuospatial deficits | — | Right hemisphere dominance for spatial processing |
| Aphasia | Rare — only if right hemisphere dominant | Most patients (right-handed) have left language hemisphere |
Amaurosis Fugax — The Right Eye Connection at I63.231
This code ties directly to the ophthalmology world! Transient right eye amaurosis fugax (curtain-like vision loss in the right eye lasting minutes) is a classic TIA symptom of right ICA disease — the ophthalmic artery is a branch of the ICA. A patient who previously had H34.211 (central retinal artery occlusion, right eye) or transient monocular vision loss in the right eye may be presenting now with a completed carotid territory stroke (I63.231). The ophthalmology encounter detecting CRAO or amaurosis fugax is a stroke-warning encounter — document the carotid connection.
NIHSS — Mandatory Additional Code
R29.7xx — NIHSS Score Must Be Coded
ICD-10-CM includes a “Use additional code” note under I63 for the National Institutes of Health Stroke Scale (NIHSS) score (R29.70-R29.742). This is not optional — when an NIHSS score is documented in the record, the corresponding R29.7xx code must be assigned as an additional code alongside I63.231.
| NIHSS Score Range | Severity | R29.7xx Code |
|---|---|---|
| 0 | No stroke symptoms | R29.700 |
| 1-4 | Minor stroke | R29.701-R29.704 |
| 5-15 | Moderate stroke | R29.705-R29.715 |
| 16-20 | Moderate-severe | R29.716-R29.720 |
| 21-42 | Severe stroke | R29.721-R29.742 |
NIHSS Severity Drives Quality Metrics — Not DRG
The NIHSS code does not directly affect DRG grouping — it is a quality/registry data element. However, it is required for:
- CMS Stroke Core Measure reporting
- Joint Commission Primary Stroke Center certification
- Get With The Guidelines-Stroke registry
- Deficit-based documentation supporting CC/MCC capture
Missing NIHSS documentation is a CDI and quality reporting gap — if the score is documented anywhere in the record (admission note, nursing assessment, ED triage), assign the R29.7xx code.
💰 HCC Risk Adjustment (CMS-HCC v28)
| Field | Detail |
|---|---|
| CMS-HCC Model Version | v28 (2024-2025 Implementation) |
| HCC Assignment | ✅ HCC 100 — Ischemic or Unspecified Stroke |
| HCC Category Name | Ischemic or Unspecified Stroke |
| RAF Coefficient | ~0.279 (verify against current CMS-HCC v28 published tables) |
| RxHCC | Check RxHCC model separately |
HCC 100 — One of the Highest Single-Code RAF Values in the Model
I63.231 maps to HCC 100 — a high-value HCC with significant RAF weight that persists into subsequent plan years when correctly documented with appropriate sequelae codes. This is critical for Medicare Advantage plans.
The acute vs. sequelae transition is the HCC continuity key:
- During acute admission: I63.231 → captures HCC 100 for the acute year
- After discharge, all subsequent encounters: I69.3x (sequelae of cerebral infarction) → continues HCC 100 capture in future years
Failure to transition to I69.3x codes at post-acute and outpatient encounters means the HCC 100 is NOT recaptured in subsequent plan years — a major RAF leakage for MA plans. Every neurology follow-up, PCP visit, and rehabilitation encounter should carry the appropriate I69.3x sequelae code.
Common HCC Comorbidities at a Stroke Admission — Sweep These
| Comorbidity | HCC (v28) | Common at Stroke Admission? |
|---|---|---|
| Atrial fibrillation | HCC 96 | ✅ High — major stroke etiology |
| Heart failure | HCC 85 | ✅ Common comorbidity |
| Type 2 DM | HCC 18 | ✅ Major stroke risk factor |
| CKD Stage 3-5 | HCC 137 | ✅ Vascular disease comorbidity |
| COPD | HCC 111 | ✅ Common elderly comorbidity |
| Hypertensive CKD | HCC 138 | ✅ When HTN + CKD both documented |
| Carotid stenosis | Not mapped | Document for quality — not HCC |
| Hemiplegia (post-stroke) | HCC 103 | ✅ If documented — high value |
| Dysphagia | HCC 103 | ✅ Post-stroke swallowing dysfunction |
Hemiplegia / Dysphagia — Acute vs. Sequelae Context
When hemiplegia (G81.x) or dysphagia (R13.10) is documented as a current deficit of the acute stroke, assign these as additional diagnoses alongside I63.231 — they function as CCs in DRG grouping AND contribute to HCC capture. Do not wait for discharge to document neurological deficits — capture them on the inpatient claim when documented during the admission.
🏥 MS-DRG Assignment
MDC 01 — Diseases and Disorders of the Nervous System
With Thrombolytic Agent (tPA/Alteplase/Tenecteplase Administered)
| DRG | Title | CC/MCC Tier | Est. Relative Weight* |
|---|---|---|---|
| DRG 061 | Ischemic Stroke, Precerebral Occlusion, or TIA with Thrombolytic + MCC | MCC | ~3.5-4.2 |
| DRG 062 | Ischemic Stroke, Precerebral Occlusion, or TIA with Thrombolytic + CC | CC | ~2.0-2.5 |
| DRG 063 | Ischemic Stroke, Precerebral Occlusion, or TIA with Thrombolytic, no CC/MCC | None | ~1.3-1.7 |
I63.231 Qualifies for DRG 061-063 When tPA Given
I63.231 classifies as a precerebral artery stroke (carotid = precerebral = extracranial). When a thrombolytic agent (3E03317 — alteplase IV, or 3E07317 — IA tPA) is administered, I63.231 as principal diagnosis groups to DRG 061/062/063 — the highest-weight stroke DRGs. These DRGs carry significantly higher relative weights than the standard stroke DRGs (064-066), reflecting the resource intensity of tPA administration and associated monitoring.
Without Thrombolytic Agent
| DRG | Title | CC/MCC Tier | Est. Relative Weight* |
|---|---|---|---|
| DRG 064 | Intracranial Hemorrhage or Cerebral Infarction with MCC or tPA in 24 hrs | MCC | ~2.5-3.2 |
| DRG 065 | Intracranial Hemorrhage or Cerebral Infarction with CC or tPA in 24 hrs | CC | ~1.5-2.0 |
| DRG 066 | Intracranial Hemorrhage or Cerebral Infarction without CC/MCC | None | ~0.9-1.2 |
*Approximate. Verify against IPPS FY2025 Final Rule MS-DRG Definitions Manual v42.
The CC/MCC Sweep Is the DRG Tier Determinant
At I63.231, the difference between DRG 064 (with MCC) and DRG 066 (without CC/MCC) can represent a payment difference of 2-3× the base rate. The CC/MCC burden from comorbidities — hypertensive heart disease, AFib, DM with complications, aspiration pneumonia, acute kidney injury — directly determines which tier the case groups to. This is where inpatient CDI for stroke cases has the greatest financial and clinical documentation impact.
CC and MCC Examples for I63.231 DRG Optimization
| Code | Description | CC or MCC? |
|---|---|---|
| I48.0/I48.11/I48.19 | Atrial fibrillation (various types) | CC |
| I50.21-I50.43 | Acute heart failure | MCC |
| J69.0 | Aspiration pneumonia | MCC |
| N17.x | Acute kidney injury | MCC (stage 3) / CC (stage 1-2) |
| G81.x | Hemiplegia/hemiparesis | CC (when documented current deficit) |
| R13.10 | Dysphagia, unspecified | CC |
| E11.65 | Type 2 DM with hyperglycemia | CC |
| K92.1 | Melena | CC |
| I26.09 | Pulmonary embolism without acute cor pulmonale | MCC |
🔗 Related ICD-10-CM Codes
Right Carotid Stroke — Mechanism Comparison
| Code | Description | Mechanism | Use When |
|---|---|---|---|
| I63.031 | Cerebral infarction, right carotid, thrombosis | In-situ clot — atherosclerotic plaque | Severe ipsilateral stenosis, no cardiac source |
| I63.131 | Cerebral infarction, right carotid, embolism | Clot from elsewhere | AFib, low EF, endocarditis, artery-to-artery |
| I63.231 | Cerebral infarction, right carotid, unspecified ← This Code | Not documented | Workup inconclusive or mechanism undocumented |
Carotid Laterality — Same Mechanism
| Code | Description |
|---|---|
| I63.232 | Cerebral infarction, left carotid, unspecified mechanism |
| I63.233 | Cerebral infarction, bilateral carotid, unspecified mechanism |
| I63.239 | Cerebral infarction, unspecified carotid, unspecified mechanism ⚠️ |
Post-Acute / Sequelae Codes — Use After Discharge
| Code | Description | When |
|---|---|---|
| I69.30 | Unspecified sequelae of cerebral infarction | Post-discharge, generic |
| I69.351 | Hemiplegia/hemiparesis following CI, right dominant | If dominant side affected |
| I69.352 | Hemiplegia/hemiparesis following CI, left dominant | Left-sided weakness sequela |
| I69.391 | Aphasia following cerebral infarction | Language deficit sequela |
| I69.398 | Other sequelae of cerebral infarction | Catch-all for other deficits |
NEVER Use I63.231 at Post-Acute or Outpatient Follow-Up Visits
I63.231 is an ACUTE phase code — it represents the active, in-progress infarction. Once the patient is discharged from the hospital after the acute stroke:
- All outpatient, rehabilitation, home health, and SNF encounters use I69.3x codes (sequelae of cerebral infarction) — NOT I63.231
- The ACUTE code is only appropriate during the inpatient stay AND any ED visits for the acute event
- Using I63.231 at a 3-month follow-up neurology office visit is a coding compliance error
- HCC 100 is STILL captured via I69.3x — the sequelae codes map to the same HCC
Carotid Disease Without Infarction
| Code | Description | When |
|---|---|---|
| I65.21 | Occlusion and stenosis of right carotid artery | Stenosis documented without acute infarction |
| G45.3 | Amaurosis fugax | Transient monocular blindness — right eye ICA TIA |
| G45.9 | TIA, unspecified | Pre-infarction transient event |
| Z86.73 | Personal history of TIA and cerebral infarction w/o residual | History only — no current sequelae |
| Z87.39 | Personal history of other circulatory system conditions | Use carefully — Z86.73 is more specific for stroke history |
🛠️ ICD-10-PCS — Procedures Commonly Associated with I63.231
IV Thrombolysis (tPA) — Most Common Acute Treatment
| ICD-10-PCS | Description | When |
|---|---|---|
| 3E03317 | Introduction of thrombolytic into peripheral vein, percutaneous | IV tPA (alteplase/tenecteplase) via peripheral IV |
Endovascular Thrombectomy — Mechanical Clot Removal
| ICD-10-PCS | Description | When |
|---|---|---|
| 03CG3ZZ | Extirpation of matter, right internal carotid artery, perc | Mechanical thrombectomy, right ICA |
| 03CH3ZZ | Extirpation of matter, left internal carotid artery, perc | If bilateral or contralateral extension |
Carotid Endarterectomy (CEA) — Surgical Plaque Removal
| ICD-10-PCS | Description | When |
|---|---|---|
| 03CG0ZZ | Extirpation of matter, right ICA, open | Open CEA, right side |
| 03BG0ZZ | Excision, right ICA, open | Open endarterectomy approach |
CEA Timing at I63.231 Admission
Carotid endarterectomy for symptomatic right ICA stenosis is most beneficial within 48 hours to 2 weeks of symptom onset. When CEA is performed during the same inpatient admission as I63.231, the ICD-10-PCS CEA code is added to the claim and significantly increases the DRG complexity and resource intensity — the case may regroup to a surgical DRG depending on the principal procedure designation.
Diagnostic Imaging
| ICD-10-PCS | Description |
|---|---|
| B030YZZ | Computerized tomography, brain (CT head) |
| B030ZZZ | Magnetic resonance imaging, brain |
| B331YZZ | Fluoroscopy, right internal carotid artery (cerebral angiogram) |
💊 Coding Scenarios
Scenario 1 — Acute Ischemic Stroke, IV tPA Given, Workup Shows AFib (Inpatient)
Clinical Vignette: A 71-year-old male presents to the ED with acute onset left hemiplegia, left facial droop, and left neglect — NIHSS 14 — onset 90 minutes ago. CT head negative for hemorrhage. CTA head/neck: right ICA severe stenosis with thrombus. IV alteplase administered. EKG: new atrial fibrillation. Echo: low EF 35%. Admission MRI: right MCA territory infarction. Neurology note: “Acute ischemic stroke, right carotid territory — likely cardioembolic given new AFib and low EF — starting anticoagulation.”
Code Check — Mechanism Query Result:
- Neurology explicitly documents cardioembolic mechanism → I63.131 (embolism of right carotid artery) is the correct code — NOT I63.231
- However, if query had not been performed, I63.231 would have been the default
Principal Diagnosis:
- I63.131 — Cerebral infarction due to embolism of right carotid artery (mechanism now specified — cardioembolic)
Additional Diagnoses:
- I48.0 — Paroxysmal atrial fibrillation (new onset — etiology of embolism)
- I50.22 — Systolic heart failure, chronic (low EF documented)
- G81.94 1 — Hemiplegia, unspecified, affecting left nondominant side (current neurological deficit — CC)
- R29.714 — NIHSS score 14 (mandatory additional code — moderate severity)
ICD-10-PCS:
- 3E03317 — IV alteplase thrombolytic administered
MS-DRG:
- DRG 061 — Ischemic Stroke/Precerebral Occlusion with Thrombolytic + MCC (heart failure = MCC)
This Scenario Shows Why the CDI Query Matters
Without the query, this case would be I63.231 + DRG 064 (no thrombolytic DRG for unspecified mechanism). With the query confirming embolism + documentation of tPA given, it correctly groups to I63.131 + DRG 061 — the highest-weight stroke DRG. Additionally, the AFib (HCC 96) and heart failure (HCC 85) are captured alongside HCC 100 from the stroke code.
Scenario 2 — Stroke, No tPA, Mechanism Not Documented (Inpatient)
Clinical Vignette: An 84-year-old female presents with acute right carotid territory stroke — NIHSS 8. She is outside the tPA window (symptom onset >4.5 hours). Carotid duplex: right ICA 70% stenosis. No AFib on telemetry. Echo ordered but not resulted before discharge. Neurology discharge summary: “Acute ischemic stroke, right carotid artery.” No mechanism (thrombosis vs. embolism) documented. CDI query sent — no response within coding window.
Principal Diagnosis:
- I63.231 — Cerebral infarction, right carotid artery, unspecified mechanism (appropriate — query sent, no response; mechanism remains unspecified)
Additional Diagnoses:
- I65.21 — Occlusion and stenosis of right carotid artery (70% stenosis — separately codeable underlying vessel disease)
- I10 — Essential hypertension (documented)
- E78.5 — Hyperlipidemia, unspecified (documented — vascular risk factor)
- R29.708 — NIHSS score 8
MS-DRG:
- DRG 066 — Cerebral Infarction without CC/MCC (no qualifying CC/MCC documented in this case)
I65.21 — Code the Carotid Stenosis Separately
When the record documents carotid stenosis (the underlying vascular disease) in addition to the acute infarction, I65.21 (right carotid stenosis/occlusion) may be assigned as an additional diagnosis — it is a separately identifiable condition that was present on admission and is clinically relevant to the stroke etiology. This is NOT a duplicate code — I63.231 classifies the infarction, while I65.21 classifies the underlying vessel disease.
Scenario 3 — Post-Discharge Neurology Follow-Up, 6 Weeks Later (Outpatient)
Clinical Vignette: The same patient from Scenario 2 presents to the outpatient neurology clinic 6 weeks post-stroke for follow-up. She has residual left arm weakness. NIHSS now 3. Physician documents: “Residual left hemiparesis following right carotid territory ischemic stroke — good recovery — continue antiplatelet therapy.”
ICD-10-CM (Outpatient Follow-Up):
- Do NOT use I63.231 — the acute stroke is resolved
- ✅ I69.352 — hemiplegia/hemiparesis following cerebral infarction, affecting left nondominant side (sequelae code — residual deficit)
- ✅ I65.21 — Right carotid stenosis (ongoing vascular disease)
- ✅ Z87.39 — Personal history of other circulatory conditions (or Z86.73 for TIA/stroke history)
Acute Code at Follow-Up = Compliance Error
Assigning I63.231 at a 6-week follow-up visit is incorrect — the acute infarction is no longer present. The sequelae code I69.352 captures the ongoing residual hemiparesis AND continues HCC 100 capture for the current plan year. Never carry acute stroke codes forward to post-discharge encounters.
⚠️ Coding Pitfalls and Tips
| Pitfall or Tip | |
|---|---|
| ❌ | Never use I63.231 at post-discharge outpatient or rehab encounters — use I69.3x sequelae codes instead |
| ❌ | Never leave mechanism unspecified without a CDI query — thrombosis (I63.031) vs. embolism (I63.131) affects DRG grouping and clinical accuracy |
| ❌ | Never omit the NIHSS code (R29.7xx) — mandatory additional code when NIHSS is documented; required for quality measure reporting |
| ❌ | Never miss the carotid stenosis code I65.21 when underlying vessel disease is documented — it is separately codeable |
| ❌ | Never code only the stroke — the full comorbidity burden (AFib, HF, DM, AKI) drives DRG tier from 064/066 up to 061/064 — sweep everything |
| ❌ | Never miss a tPA administration — IV alteplase (3E03317) changes DRGs 064-066 to 061-063 — a massive payment differential; confirm with pharmacy records if not in physician note |
| ✅ | Query mechanism first — thrombosis or embolism? If AF or low EF is documented → likely embolism → I63.131 |
| ✅ | Code current neurological deficits — hemiplegia (G81.x), dysphasia (R47.01), dysphagia (R13.10) — these are CCs that drive DRG tier |
| ✅ | Code the NIHSS — R29.7xx every acute stroke admission — mandatory and required for Joint Commission/stroke certification |
| ✅ | HCC 100 is gold — capture it every year via I69.3x at all post-acute encounters in MA patients |
| ✅ | Amaurosis fugax connection — right eye transient monocular vision loss (G45.3) = right ICA TIA → may be the predecessor event to I63.231 |
| ✅ | CEA during same admission — if right ICA endarterectomy performed, add ICD-10-PCS CEA code; case may regroup to surgical MDC |
| ✅ | Aspiration pneumonia (J69.0) — extremely common post-stroke complication; MCC — document swallowing evaluation and results |
📚 Sources
1. CMS/NCHS. ICD-10-CM Official Guidelines for Coding and Reporting, FY2025. Section I.B.4 — Coding to highest level of specificity; Section I.B.13 — Laterality. I63 tabular — “Use additional code for NIHSS (R29.70-R29.742).” I63.2x family structure — unspecified occlusion or stenosis, precerebral arteries.
2. CMS. IPPS Final Rule FY2025 — MS-DRG Definitions Manual v42. MDC 01 — Diseases and Disorders of the Nervous System. DRG 061-063: Ischemic stroke/precerebral occlusion with thrombolytic agent, MCC/CC/none. DRG 064-066: Intracranial hemorrhage or cerebral infarction, MCC/CC/none.
3. CMS. CMS-HCC Risk Adjustment Model v28 — ICD-10-CM Mappings, 2024-2025. I63.231 → HCC 100 (Ischemic or Unspecified Stroke). RAF coefficient for HCC 100 — verify current published tables.
4. ICD-10-CM Tabular List. I63.231 — Cerebral infarction due to unspecified occlusion or stenosis of right carotid artery. 6-character billable code. Excludes 1: I69.3x (sequelae — use after acute phase). Parent codes I63.23 (5-char) and I63.2 (4-char) non-billable headers.
5. American Heart Association / American Stroke Association. 2023 Guideline for the Management of Patients with Acute Ischemic Stroke. Thrombolysis window 4.5 hours; mechanical thrombectomy criteria; NIHSS scoring and documentation requirements; carotid endarterectomy timing for symptomatic stenosis.
6. ICD-10-CM Tabular — I65.21: Occlusion and stenosis of right carotid artery — separately codeable underlying vessel disease in carotid-territory stroke.
7. ICD-10-CM Tabular — R29.70-R29.742: NIHSS score codes — “Use additional code” instruction confirmed under I63 category.
8. ICD-10-PCS FY2025 — 3E03317: Introduction of thrombolytic, peripheral vein, percutaneous. 03CG3ZZ: Extirpation, right internal carotid artery, percutaneous — mechanical thrombectomy.