Coronary Artery Disease ICD-10 Codes (I25)

Coronary Artery Disease (CAD) is the leading cause of mortality worldwide and the most frequent diagnosis evaluated and treated in the cardiac catheterization laboratory. In ICD-10-CM, atherosclerotic cardiovascular disease is classified under category I25 (Chronic ischemic heart disease). Precise coding requires documenting whether disease involves native vessels or coronary artery bypass grafts (CABG), the presence and clinical stability of angina pectoris, prior stent placements, in-stent restenosis, and chronic total occlusions. This comprehensive guide details the full I25 coding structure, combination codes, bypass graft rules, and procedural documentation standards.

Native Vessel CAD and Combination Codes (I25.10 – I25.119)

In ICD-10-CM, coronary artery disease of native coronary arteries is reported using the I25.1- series. The coding classification incorporates an essential coding rule: Combination Coding for CAD with Angina.

Coronary Bypass Graft Atherosclerosis Codes (I25.7 & I25.81)

When a patient with a history of Coronary Artery Bypass Graft (CABG) surgery develops atherosclerosis in their bypass conduits, dedicated subcategories distinguish the graft type and angina status:

Hierarchical Coding Rule for Post-CABG Patients: If an angiogram reveals disease in both native coronary arteries and bypass grafts, the bypass graft code (I25.7- / I25.81-) takes sequencing precedence if the intervention was performed on the bypass graft.

Chronic Total Occlusion (CTO) and In-Stent Restenosis (ISR)

Specialized coronary pathologies require secondary diagnosis codes:

• Chronic Total Occlusion (CTO) — Code I25.82:
  • Assigned when a coronary artery has been 100% occluded with TIMI 0 flow for ≥3 months.
  • Secondary Code Rule: Code I25.82 is an add-on diagnosis code that must be sequenced after the primary underlying CAD code (e.g., I25.10 or I25.110). It supports the medical necessity for specialized CTO PCI techniques (CPT 92943).
• Coronary In-Stent Restenosis (ISR):
  • When a previously deployed coronary stent develops >50% luminal narrowing due to neointimal hyperplasia or neoatherosclerosis, coding depends on whether an active complication is reported:
  • T82.855A: Stenosis of coronary artery stent, initial encounter.
  • Followed by the CAD with angina code (e.g., I25.110 or I25.118) to fully capture the clinical presentation.

Prior Revascularization & Myocardial Infarction History Codes

Capturing the patient's past surgical and interventional history is essential for hierarchical condition categories (HCC) and risk stratification:

Sequencing Rules: Acute Myocardial Infarction vs Underlying CAD

When a patient presents with an acute STEMI or NSTEMI on a background of chronic coronary artery disease, strict official ICD-10 sequencing guidelines apply:

1. Acute MI is ALWAYS the Principal / Primary Diagnosis: The acute infarction code (e.g., I21.02 STEMI of LAD or I21.4 NSTEMI) must be sequenced as the primary diagnosis driving the hospital admission.
2. Underlying CAD is Sequenced as a Secondary Diagnosis: Report the underlying atherosclerotic heart disease (I25.10) as a secondary diagnosis.
3. Never Code Angina with Acute MI: Do not assign I25.110 (CAD with unstable angina) when the patient has suffered an acute MI. The acute infarction subsumes the ischemic angina presentation.

Physician Documentation Checklist for Clean Billing

To ensure full compliance and avoid claim denials for coronary catheterization and revascularization:

• Specify Native vs Graft Anatomy: Always state whether atherosclerosis involves native arteries (LAD, LCx, RCA, LM) or bypass conduits (SVG to OM, LIMA to LAD).
• Document Angina Type and Functional Class: State whether angina is unstable (rest pain, accelerating), stable exertional (CCS Class I–IV), or vasospastic.
• Document Lesion Severity & Hemodynamics: Record exact percent diameter stenosis (≥70% or ≥50% for left main), fractional flow reserve (FFR ≤0.80 / iFR ≤0.89), and intravascular ultrasound (IVUS MLA <3.5 mm² or <6.0 mm² for LM).
• Capture Chronic Occlusion Duration: If a chronic total occlusion is treated, chart that the occlusion has been present for >3 months to justify code I25.82 and CTO PCI reimbursement.

Summary and Key Takeaways

• Atherosclerotic coronary artery disease is classified under ICD-10 category I25.
• Native CAD with angina requires a combination code (I25.110–I25.119); do NOT report separate codes for CAD and angina.
• Post-CABG bypass graft atherosclerosis is coded in series I25.7- (with angina) and I25.81- (without angina).
• Chronic total occlusion is coded as secondary add-on diagnosis I25.82.
• In acute STEMI/NSTEMI encounters, sequence the acute MI code (I21.-) as principal and CAD (I25.10) secondarily.
• History codes Z95.5 (prior stent) and Z95.1 (prior CABG) provide vital risk adjustment data.

Frequently asked questions

What is the most common ICD-10 code for Coronary Artery Disease (CAD)?

The most common code is I25.10 (Atherosclerotic heart disease of native coronary artery without angina pectoris). If the patient has unstable angina, use I25.110. If stable exertional angina is present, use I25.118.

Can you bill I25.10 (CAD) and I20.0 (Unstable Angina) together?

No. ICD-10-CM guidelines mandate using the combination code I25.110 (Atherosclerotic heart disease of native coronary artery with unstable angina) rather than two separate codes.

What is the ICD-10 code for a Chronic Total Occlusion (CTO) of a coronary artery?

The ICD-10-CM code for a Chronic Total Occlusion is I25.82. It is an add-on secondary diagnosis code that must be sequenced after the primary CAD code (such as I25.10 or I25.110).

What is the ICD-10 code for disease in a Saphenous Vein Graft (SVG)?

Atherosclerosis of an autologous vein bypass graft with unstable angina is coded as I25.700. If the vein graft disease is stable/without angina, use code I25.810.

What is the ICD-10 code for disease in a LIMA or RIMA graft?

Atherosclerosis of an autologous internal mammary artery graft with unstable angina is coded as I25.710. Without angina, use code I25.811.

What is the ICD-10 code for a history of prior coronary stent placement?

The ICD-10-CM code for presence of coronary angioplasty implant and stent is Z95.5.

What is the ICD-10 code for a history of prior CABG surgery?

The ICD-10-CM code for presence of aortocoronary bypass graft(s) is Z95.1.

How do you code an Acute MI in a patient with known CAD?

Sequence the Acute MI code first as the principal diagnosis (such as I21.02 for anterior STEMI or I21.4 for NSTEMI), followed by I25.10 (CAD without angina) as a secondary diagnosis.

What is the ICD-10 code for In-Stent Restenosis (ISR)?

Coronary in-stent restenosis is coded as T82.855A (Stenosis of coronary artery stent, initial encounter), accompanied by the appropriate CAD/angina code (such as I25.110 or I25.118).