🧬 ICD-10 CM I82.4Z1 — Acute Embolism and Thrombosis of Unspecified Deep Veins of Right Distal Lower Extremity
Billable Code Confirmed
ICD-10 CM I82.4Z1 is a fully specified, 7-character billable code. The 6th character “Z” identifies the vein group as unspecified deep veins of the distal (below-the-knee) lower extremity, and the 7th character “1” specifies right-sided involvement, satisfying both the laterality and site-depth requirements for this code family.
Non-Billable Parent Codes
I82.4 is category-level only and cannot be billed — it lacks the 6th-character vein-group specificity and 7th-character laterality required for a complete code. I82.4Z is missing only the 7th-character laterality digit and is not billable on its own; it must terminate in 1, 2, 3, or 9. I82 (Other venous embolism and thrombosis) is a chapter-level category header with no direct billing use.
Clinical Context
The distinction driving this code is anatomic depth (distal/below-knee vs. proximal/above-knee) combined with the fact that the specific calf vein (posterior tibial, peroneal, anterior tibial, or muscular/soleal/gastrocnemius) was not individually identified in the documentation — if a named calf vein is documented, a more specific code in the I82.4A–I82.4X range should be assigned instead.
Code Classification
This is a diagnosis code (ICD-10-CM), not a procedure code. It reports the clinical condition of acute distal DVT and does not by itself authorize or describe any treatment, imaging, or intervention.
🔍 Code Description
ICD-10 CM I82.4Z1 captures an acute thrombus obstructing one or more of the paired deep calf veins on the right side — the posterior tibial, anterior tibial, peroneal, or muscular (soleal/gastrocnemius) veins — when the operative or clinical note does not name the specific vein involved. This contrasts with I82.4A1-type codes (specific named vein) and with proximal DVT codes like I82.401 (femoral/popliteal group, unspecified vein, right), which carry a materially higher risk of embolization to the lungs and different anticoagulation duration recommendations per current vascular medicine guidance. “Distal” DVT is also referred to clinically as isolated calf-vein thrombosis, and its natural history (lower propagation and PE risk than proximal disease) is part of why the code family is split at this anatomic boundary rather than lumped with I82.401.
Clinically, right distal DVT typically presents with unilateral calf swelling, tenderness, and warmth, and is confirmed by compression duplex ultrasound of the deep venous system. It must be distinguished from I80.221 (phlebitis and thrombophlebitis of right tibial vein), which describes an inflammatory superficial-thrombophlebitis-type process rather than a frank thrombotic occlusion, and from chronic disease coded to I82.5Z1 when imaging or documentation indicates a longstanding, organized (rather than acute) thrombus.
🌳 Code Tree / Hierarchy
I82.4 Acute embolism and thrombosis of deep veins of lower extremity ❌ Non-billable
│
├── I82.40 Acute embolism and thrombosis of unspecified deep veins of unspecified lower extremity ❌ Non-billable
│ └── I82.409 Acute embolism and thrombosis of unspecified deep veins of unspecified lower extremity ✅ Billable
│
├── I82.41 Acute embolism and thrombosis of femoral vein ❌ Non-billable
│ └── I82.411 Acute embolism and thrombosis of right femoral vein ✅ Billable
│
├── I82.4Y Acute embolism and thrombosis of unspecified deep veins of proximal lower extremity ❌ Non-billable
│ └── I82.4Y1 Acute embolism and thrombosis of unspecified deep veins of right proximal lower extremity ✅ Billable
│
├── I82.4Z Acute embolism and thrombosis of unspecified deep veins of distal lower extremity ❌ Non-billable
│ │
│ ├── I82.4Z1 Acute embolism and thrombosis of unspecified deep veins of right distal lower extremity ◀ THIS CODE ✅ Billable
│ ├── I82.4Z2 Acute embolism and thrombosis of unspecified deep veins of left distal lower extremity ✅ Billable
│ ├── I82.4Z3 Acute embolism and thrombosis of unspecified deep veins of distal lower extremity, bilateral ✅ Billable
│ └── I82.4Z9 Acute embolism and thrombosis of unspecified deep veins of unspecified distal lower extremity ✅ Billable
│
└── I82.42 Acute embolism and thrombosis of iliac vein ❌ Non-billable
└── I82.421 Acute embolism and thrombosis of right iliac vein ✅ BillableDistal vs. Proximal Specificity Drives Anticoagulation Duration
Payers and vascular specialty guidelines treat isolated distal (calf) DVT differently from proximal DVT for anticoagulation duration and follow-up imaging decisions — miscoding a documented proximal (femoral/popliteal) clot as I82.4Z1 understates clinical severity and can trigger a coding-accuracy or medical-necessity audit flag.
Tip
Always check the duplex ultrasound report, not just the H&P, for the specific vein name — radiology frequently documents the exact vein (e.g., “peroneal vein thrombus”) even when the admitting note simply says “calf DVT,” which would support a more specific code than I82.4Z1.
✅ Includes
- Acute thrombosis of one or more unnamed distal deep veins of the right lower leg, including presentations documented simply as “right calf DVT” or “right below-knee DVT” without further vein specification.
- New (not chronic or resolving) clot formation confirmed by imaging, distinguished from chronic/organized thrombus which would code to I82.5Z1.
❌ Excludes
Excludes 1
No Excludes1 conditions are listed for I82.4Z1 in the FY2026 ICD-10-CM tabular.
Excludes 2
I82.42-series (iliac vein) and I82.43-series (popliteal vein) — 2-3 sentences: These represent proximal, not distal, deep veins and are structurally separate code families; they may be coded together with I82.4Z1 if a patient has simultaneous proximal and distal thrombus, since they describe genuinely distinct anatomic sites rather than duplicative reporting of the same clot. Z79.01 (long-term current use of anticoagulants) — Frequently reported alongside I82.4Z1 when the patient is on established anticoagulation; this is a status code, not a mutually exclusive diagnosis, and both may be coded together when clinically supported.
📋 Clinical Overview
Distal vs. Proximal DVT
Distinguishing distal from proximal DVT is the single most consequential clinical decision point in this code family, since it changes both the ICD-10-CM code selected and the downstream treatment duration and PE-risk stratification.
| Feature | I82.4Z1 | I82.401 (Proximal, unspec. vein, right) | I82.411 (Femoral vein, right) |
|---|---|---|---|
| Anatomic location | Below-knee (calf) veins, unnamed | Above-knee, unnamed vein | Above-knee, femoral vein specifically named |
| PE risk | Lower; embolization risk rises mainly with proximal extension | Higher | Higher |
| Typical anticoagulation | Often shorter course, sometimes surveillance-only per vascular guidance | Standard-duration anticoagulation | Standard-duration anticoagulation |
Important
A CDI query is warranted whenever the note documents “DVT” without stating acute vs. chronic, or without specifying calf vs. thigh-level involvement — both distinctions change the code family entirely (I82.4 vs. I82.5, and Z-group vs. named-vein/proximal group).
Manifestations & Symptom Burden
- Unilateral calf swelling and increased limb circumference compared to the contralateral leg.
- Localized tenderness or pain along the deep venous course, often worsened by dorsiflexion.
- Warmth and mild erythema over the affected calf.
- Low-grade fever may accompany extensive thrombus burden.
Tip
💰 HCC Risk Adjustment
The I82.4- acute lower-extremity DVT family, including I82.4Z1, maps to HCC 267 (Deep Vein Thrombosis and Pulmonary Embolism) under CMS-HCC V28 (100% phased in for payment year 2026), carrying a community, non-dual, aged base RAF weight of approximately 0.294. Because this is an acute-episode HCC rather than a chronic-condition HCC, capture depends entirely on that specific encounter’s documentation showing active management (anticoagulation initiation/adjustment, imaging confirmation, or a stated treatment plan) — it does not persist automatically into future encounters the way a chronic HCC would, so each qualifying visit needs its own MEAT documentation.
🏥 MS-DRG Assignment
As principal diagnosis, I82.4Z1 falls under MDC 05 (Diseases and Disorders of the Circulatory System), grouping to MS-DRG 299 (Peripheral Vascular Disorders w MCC), MS-DRG 300 (w CC), or MS-DRG 301 (w/o CC/MCC) depending on secondary diagnoses present on the claim. There is no dedicated national NCD specific to the I82.4Z1 diagnosis code itself; however, coders should check the applicable Noridian (JE/JF) LCD for lower-extremity venous duplex ultrasound (the confirmatory diagnostic study) for coverage/medical-necessity edits, and confirm anticoagulant therapy documentation supports ongoing medical necessity if home infusion or DME (e.g., compression devices) is billed alongside the inpatient stay.
- Verify secondary diagnoses (concurrent PE, active GI bleed on anticoagulation, sepsis) that would elevate the DRG to the MCC tier.
- Confirm the admitting diagnosis narrative supports DVT as principal rather than as a secondary complication of another admitting condition (e.g., post-surgical DVT, which may require a different principal diagnosis sequencing per UHDDS).
🔗 Related ICD-10-CM Codes
Same-family distal DVT, other laterality/site:
- I82.4Z2 — Acute embolism and thrombosis of unspecified deep veins of left distal lower extremity
- I82.4Z3 — Acute embolism and thrombosis of unspecified deep veins of distal lower extremity, bilateral
- I82.4Z9 — Acute embolism and thrombosis of unspecified deep veins of unspecified distal lower extremity
- I82.5Z1 — Chronic embolism and thrombosis of unspecified deep veins of right distal lower extremity
Proximal and named-vein comparators:
- I82.401 — Acute embolism and thrombosis of unspecified deep veins of right proximal lower extremity
- I82.411 — Acute embolism and thrombosis of right femoral vein
- I82.431 — Acute embolism and thrombosis of right popliteal vein
- I80.221 — Phlebitis and thrombophlebitis of right tibial vein
- Z79.01 — Long-term (current) use of anticoagulants
🛠️ Commonly Associated CPT Codes
- 93971 — Duplex scan of extremity veins, unilateral or limited study; the primary confirmatory diagnostic test for I82.4Z1.
- 93970 — Duplex scan of extremity veins, complete bilateral study; used when both legs are evaluated regardless of laterality of the ultimate diagnosis.
- 36000 — Introduction of needle or intracatheter into a vein; commonly bundled when establishing IV access for anticoagulation, not separately billable with most inpatient E/M without a distinct purpose.
- 37187 — Percutaneous transluminal mechanical thrombectomy, vein(s); used only if catheter-directed thrombolysis/thrombectomy is performed for extensive or limb-threatening distal DVT.
- 37191 — Insertion of intravascular vena cava filter; reported when an IVC filter is placed due to anticoagulation contraindication.
- 37193 — Retrieval (removal) of intravascular vena cava filter; reported at a later encounter when the filter is removed.
🏷️ Modifier Reference
| Modifier | Name | When to Apply |
|---|---|---|
| -RT | Right Side | Appended to the duplex ultrasound or vascular intervention CPT code when only the right lower extremity is studied or treated, matching the right-sided laterality of I82.4Z1. |
| -59 | Distinct Service | Applied if a separately identifiable procedure (e.g., IVC filter placement) is performed at a distinct session from the diagnostic duplex on the same date and NCCI edits would otherwise bundle them. |
| -25 | Significant E/M | Used on an E/M code when a significant, separately identifiable evaluation is performed on the same day as a minor vascular procedure related to this diagnosis. |
NCCI Bundling Considerations
Diagnostic duplex ultrasound (93971) performed to confirm the DVT is generally not bundled with routine inpatient E/M services, but is bundled into same-session interventional procedures (e.g., 37187) when performed purely for procedural guidance rather than as an independent diagnostic study — modifier -59 or a more specific X{EPSU} modifier is required to unbundle only when medical necessity for a separate diagnostic study is clearly documented.
💊 Coding Scenarios and Examples
Example 1
Clinical Scenario: A 68-year-old male is admitted with right calf swelling and pain. Compression duplex ultrasound confirms an acute thrombus in the right posterior tibial vein, but the radiology report and physician documentation do not further characterize which specific distal vein cluster is involved beyond “distal deep venous system.” He is started on therapeutic enoxaparin.
| Field | Code | Rationale |
|---|---|---|
| CPT | 93971 | Duplex ultrasound confirming the diagnosis. |
| PDx | I82.4Z1 | Acute, right-sided, distal deep vein thrombosis with unnamed specific vein per documentation. |
Tip
If the final radiology impression specifically names “posterior tibial vein,” a more specific code (e.g., within the I82.4A–I82.4X range for named calf veins) should be queried and used instead of I82.4Z1.
Example 2
Clinical Scenario: A 74-year-old female with a history of long-term warfarin use for prior venous thromboembolism is admitted with new right calf swelling despite therapeutic INR. Duplex ultrasound shows acute right distal DVT of unspecified vein. Anticoagulation is adjusted and a hematology consult is obtained.
| Field | Code | Rationale |
|---|---|---|
| CPT | 93971 | Diagnostic duplex confirming acute distal DVT. |
| CPT 2 | 99223 | Initial inpatient E/M reflecting the complexity of managing breakthrough clot on established anticoagulation. |
| PDx | I82.4Z1 | Principal diagnosis; reason for this admission. |
Tip
Report Z79.01 as a secondary diagnosis to capture the long-term anticoagulant status, which is clinically relevant to the breakthrough-clot narrative and supports medical necessity for anticoagulation adjustment. CDI note: confirm whether the note supports “acute-on-chronic” thrombus, which would still be coded as acute (I82.4Z1) per ICD-10-CM guidance that acute takes precedence when both are documented concurrently at the same site.
Example 3
Clinical Scenario: A 55-year-old post-operative orthopedic patient develops right calf swelling on post-op day 3. Duplex confirms acute distal DVT, unspecified vein. Given active surgical wound concerns, an IVC filter is placed instead of starting anticoagulation.
| Field | Code | Rationale |
|---|---|---|
| CPT | 37191 | IVC filter insertion performed due to anticoagulation contraindication. |
| PDx | I82.4Z1 | Principal diagnosis prompting the filter placement. |
Tip
Sequencing: if this DVT is determined to be a postoperative complication, review whether a Chapter 19 postprocedural complication code should be sequenced first per facility-specific guidelines and payer requirements — this requires explicit provider documentation linking the DVT to the surgical procedure, not coder inference.
⚠️ Coding Pitfalls and Tips
- Pitfall 1: Assigning I82.4Z1 when the duplex report actually names a specific calf vein (e.g., peroneal, posterior tibial); Tips: Always cross-check the imaging report against the code description — a named-vein code is more specific and should be used when supported.
- Pitfall 2: Confusing acute (I82.4-) with chronic (I82.5-) DVT coding; Tips: Query the provider whenever “DVT” appears without an explicit acute/chronic qualifier, since duration of symptoms alone is not sufficient per Coding Clinic guidance.
- Pitfall 3: Defaulting to I82.4Z9 (unspecified laterality) when the chart clearly documents right-sided involvement; Tips: Review the H&P, nursing notes, and imaging report together — laterality is often stated in one document even when omitted from another.
- Pitfall 4: Failing to capture Z79.01 when the patient is on established long-term anticoagulation; Tips: This status code supports medical necessity for anticoagulation management and should be reported whenever documentation supports ongoing use.
- Pitfall 5: Coding I82.4Z1 as a secondary/incidental finding when it was actually the reason for admission; Tips: Apply UHDDS principal diagnosis guidelines — if DVT prompted admission, it should be sequenced as principal even if other chronic conditions are more clinically severe.
- Pitfall 6: Missing HCC capture because MEAT criteria weren’t documented for this encounter; Tips: Confirm the note shows active monitoring, evaluation, assessment, or treatment specific to the DVT, not just a passing mention in the problem list.
📚 Sources
1. Centers for Medicare & Medicaid Services and National Center for Health Statistics. *ICD-10-CM FY2026 Code Tables and Tabular Index.* CMS/NCHS; 2026. 2. AAPC/Codify. *I82.4Z1 — Acute embolism and thrombosis of unspecified deep veins of right distal lower extremity.* AAPC; 2026. https://www.aapc.com/codes/icd-10-codes/I82.4Z1 3. HCC Buddy. *CMS-HCC V28 Mapping — I82.4-series (Deep Vein Thrombosis and Pulmonary Embolism, HCC 267).* 2026. https://hccbuddy.com 4. American Medical Association. *Current Procedural Terminology (CPT) 2026 Professional Edition.* AMA; 2026.Sources listed above correspond to superscript citations throughout this note. Verify all Medicare payment figures against your current CMS PFS Lookup tool and applicable MAC LCD prior to claim submission. Please use the latest AAPC/AHIMA Coding Books to verify each code within this note.