What does ICD-10-CM code I21.4 mean?
I21.4 represents Non-ST elevation (NSTEMI) myocardial infarction. This cardiovascular condition is classified under Chapter 9 (Diseases of the Circulatory System) and is one of the most commonly coded circulatory system diagnoses. Coders frequently reference this code as nstemi icd 10.
This is classified as a critical acute condition that typically requires urgent evaluation and treatment. This diagnosis qualifies as a Major Complication or Comorbidity (MCC) under the MS-DRG system, which significantly impacts inpatient reimbursement.
Code category and hierarchy
- Chapter: 9 – Diseases of the Circulatory System (I00-I99)
- Category: I21
- Code: I21.4 – Non-ST elevation (NSTEMI) myocardial infarction
Guideline notes and coding considerations
Important Guideline Note
I21.4 is a Major Complication or Comorbidity (MCC). Ensure clinical documentation clearly supports the diagnosis severity and specificity.
- Use Additional Code: code, if applicable, to identify:; exposure to environmental tobacco smoke ( Z77.22 ); history of tobacco dependence ( Z87.891 )
Learn the underlying rules in the ICD-10 Coding Guidelines, Combination Code Requirements, Risk Adjustment & MEAT Documentation.
Documentation tips (what coders should confirm)
- Verify the clinical documentation supports the use of I21.4
- Use additional code: code, if applicable, to identify: | exposure to environmental tobacco smoke ( Z77.22 ) | history of tobacco dependence (
- This code is an MCC — ensure documentation clearly supports the diagnosis severity
- This is a risk-adjusted diagnosis — ensure annual documentation with MEAT criteria (Monitor, Evaluate, Assess/Address, Treat)
Audit risk
As an MCC, I21.4 significantly increases DRG weight. Auditors closely review MCC codes to ensure documentation clearly supports the clinical severity. Ensure the condition is confirmed (not suspected) and actively managed during the encounter.
Validate I21.4 Against ICD 10 CM Coding Guidelines
Check this code against official guidelines for conflicts and compliance issues.
Risk adjustment and HCC mapping
HCC Impact
I21.4 (Non-ST elevation (NSTEMI) myocardial infarction) maps to the following HCC categories: CMS-HCC V24: HCC 86, CMS-HCC V28: HCC 228, RxHCC V08: HCC 188, ESRD V24: HCC 86. Proper documentation using MEAT criteria (Monitor, Evaluate, Assess/Address, Treat) is required for each encounter to support risk-adjusted diagnoses.
Learn more about risk adjustment documentation in our Risk Adjustment & MEAT Documentation Guide.
Related ICD-10 codes
Frequently Asked Questions
The ICD-10-CM code for nstemi is I21.4, which represents non-st elevation (nstemi) myocardial infarction. Verify this code using the ICD Code Auditor to ensure guideline compliance.
Yes. I21.4 is an active ICD-10-CM diagnosis code used to classify non-st elevation (nstemi) myocardial infarction for clinical documentation, reporting, and medical billing purposes.
Use the ICD Code Auditor to check I21.4 against official ICD-10-CM coding guidelines. The tool validates by fiscal year and patient gender to identify potential conflicts.
Yes. I21.4 (Non-ST elevation (NSTEMI) myocardial infarction) qualifies as an MCC under the MS-DRG system, which can significantly impact inpatient hospital reimbursement by increasing the DRG weight.
Yes. I21.4 maps to HCC 86 in the CMS-HCC V24 model, and HCC 228 in V28. Accurate coding of this condition directly impacts RAF scores for Medicare Advantage plans. Ensure documentation demonstrates the condition was evaluated and managed during the encounter.
Documentation should clearly describe the clinical condition represented by I21.4 (Non-ST elevation (NSTEMI) myocardial infarction). Include relevant clinical findings, diagnostic test results, provider assessment, and the treatment plan. The diagnosis must be supported by the medical record and not based solely on lab results without clinical interpretation.
Sources
Reviewed by: Certified ICD-10 Coding & Risk Adjustment Specialist
Learn more about our Clinical Coding Review Process