Quick answer: In medical coding, MCC stands for Major Complication or Comorbidity. An MCC is a secondary diagnosis that CMS has designated as significantly increasing the resources needed to treat a hospital inpatient. When a valid MCC is coded, the stay can group to a higher-weighted MS-DRG, which raises the hospital’s payment.
Understanding MCC and How It Is Used
MCCs are part of the Medicare Severity Diagnosis Related Group (MS-DRG) system that Medicare and many other payers use to pay hospitals for inpatient stays. CMS assigns every ICD-10-CM diagnosis code a severity level: MCC, CC (complication or comorbidity) or non-CC. The lists are updated each fiscal year, so the FY2027 MS-DRG version (effective October 1, 2026) is the one to use for current discharges.
For example, a patient admitted for pneumonia who also develops acute respiratory failure with hypoxia (J96.01) has an MCC. That stay requires more monitoring, oxygen support and length of stay than pneumonia alone, and the MS-DRG reflects it.
MCC vs CC vs Non-CC
| Severity level | What it means | Effect on MS-DRG |
| MCC | Major complication or comorbidity | Highest-weighted DRG in the family, when one exists |
| CC | Complication or comorbidity | Middle-weighted DRG |
| Non-CC | No added severity | Base DRG |
Many MS-DRGs come in families of three. Simple pneumonia and pleurisy is a good example: MS-DRG 193 is with MCC, 194 is with CC and 195 is without CC or MCC. One well-documented secondary diagnosis can move the case between them.
Examples of MCCs and CCs
Whether a condition is an MCC often depends on its exact code, so specificity matters:
| Code | Description | Severity |
| A41.9 | Sepsis, unspecified organism | MCC |
| R65.21 | Severe sepsis with septic shock | MCC |
| J96.01 | Acute respiratory failure with hypoxia | MCC |
| E43 | Unspecified severe protein-calorie malnutrition | MCC |
| G93.41 | Metabolic encephalopathy | MCC |
| I50.21 | Acute systolic (congestive) heart failure | MCC |
| I50.22 | Chronic systolic (congestive) heart failure | CC |
| N17.0 | Acute kidney failure with tubular necrosis | MCC |
| N17.9 | Acute kidney failure, unspecified | CC |
| E87.1 | Hypo-osmolality and hyponatremia | CC |
Notice the pattern: acute heart failure is an MCC while chronic heart failure is a CC, and acute kidney failure is only an MCC when tubular necrosis is documented. Always confirm severity in the current MS-DRG Definitions Manual or your encoder, because CMS changes these designations.
How MCCs Affect Coding and Reimbursement
- DRG assignment: A secondary diagnosis designated as an MCC can move the case to the highest-weighted DRG in its family.
- Severity of illness and risk of mortality: MCCs raise the SOI and ROM scores used in quality reporting and APR-DRG systems.
- Case mix index (CMI): Hospitals that accurately capture MCCs show a case mix that reflects how sick their patients really are.
- Audits: Because MCCs raise payment, they are a frequent target of payer audits and clinical validation denials.
Rules That Can Cancel an MCC
- It must be a secondary diagnosis. The principal diagnosis does not count as its own MCC.
- CC exclusions. A secondary diagnosis that is closely related to the principal diagnosis may be excluded from acting as a CC or MCC for that case.
- Present on admission (POA). Certain hospital-acquired conditions that were not present on admission do not count toward a higher DRG for Medicare.
- Clinical validation. Payers may deny an MCC if the record does not clinically support it, even when the provider wrote the diagnosis.
Tips for Coders
- Verify documentation: The provider must document the condition. Coders cannot assign an MCC from lab values or vital signs alone.
- Code to the highest specificity: Acuity (acute, chronic, acute on chronic) and type often decide whether a code is an MCC, a CC or neither.
- Query when needed: If lab results or treatment suggest a condition the provider has not documented, send a compliant, non-leading query. See our guide on how to write a provider query.
- Know the current lists: Use the MS-DRG version that matches the discharge date.
Frequently Asked Questions About MCCs
What does MCC stand for in medical coding?
MCC stands for Major Complication or Comorbidity, a secondary diagnosis that increases the MS-DRG for an inpatient stay.
What is the difference between a CC and an MCC?
Both are secondary diagnoses that add severity. An MCC has the greater impact and can move the case into the highest-weighted DRG, while a CC moves it into the middle tier.
Is sepsis an MCC?
Yes, sepsis codes such as A41.9 are MCCs when reported as a secondary diagnosis. When sepsis is the principal diagnosis, it drives its own DRG instead.
Do MCCs apply to outpatient or physician coding?
No. MCCs are part of the inpatient MS-DRG system. Outpatient and professional services are paid using CPT, HCPCS and other payment systems.
Where can I find the official MCC list?
CMS publishes the CC and MCC lists with the MS-DRG Definitions Manual and the annual IPPS final rule each fiscal year.
Related Reading
Learn more in our posts on medical coding and DRGs, severity of illness and sepsis coding. Ready to build these skills? Our instructor-led online medical coding classes and CPC certification training prepares you for the CPC exam, with workforce funding available in 30+ states.