ICD-10 C45.1
Billable / Specific HCC v28: 9 CCMesothelioma of peritoneum
About ICD-10-CM C45.1
ICD-10-CM code C45.1 represents Mesothelioma of peritoneum. This is a billable/specific code in the Neoplasms chapter (block C45). The 2026 edition of ICD-10-CM C45.1 became effective on October 1, 2025.
Coding Tips for C45.1
Specialist guidance from the PayerReady Medical Coding Team. Specificity warnings, HCC capture rules, sequencing notes.
C45.1 is a CMS-HCC v28 risk-adjustment code (category 9). To count for the patient Risk Adjustment Factor (RAF), document the diagnosis with MEAT language each calendar year: Monitored, Evaluated, Assessed, Treated. A diagnosis on the problem list alone does not satisfy CMS RADV audit standards. Include the diagnosis in the assessment with current status and current treatment plan.
C45.1 is designated CC for MS-DRG grouping. On inpatient claims, this code can shift the DRG to the with-CC variant when documented as a present-on-admission secondary diagnosis. Hospital CDI programs flag CC opportunities during chart review. Failure to capture this code may leave 30 to 80 percent of the inpatient stay revenue unrealized.
Inclusion Terms / Approximate Synonyms
Clinical terms and conditions classified under C45.1. Per CMS ICD-10-CM Tabular 2026.
- Mesothelioma of cul-de-sac
- Mesothelioma of mesentery
- Mesothelioma of mesocolon
- Mesothelioma of omentum
- Mesothelioma of peritoneum (parietal) (pelvic)
Type 1 Excludes
Pure excludes, these codes can never be coded together with C45.1. The conditions are mutually exclusive (e.g., congenital vs acquired forms).
- other malignant neoplasm of soft tissue of peritoneum (C48.-)
Medicare Advantage HCC Impact
Capture this diagnosis annually for accurate risk adjustment. Missed HCC captures are the #1 revenue leak in Medicare Advantage risk programs.
Inpatient DRG Impact, CC
codes Mesothelioma of peritoneum. As a Complication/Comorbidity (CC), this contributes to DRG severity adjustment when documented alongside the principal diagnosis.
Medicare LCD Coverage for C45.1
Local Coverage Determinations (LCDs) from CMS MACs that list C45.1 as a covered diagnosis.
Showing top 10 of 873 total . Click a CPT for full coverage scope.
Commercial Payer Coverage
Coverage policies from major commercial payers referencing C45.1.
5 Medicare
CPT Codes Commonly Billed with C45.1
Procedures frequently paired with this diagnosis based on PayerReady's Dx↔Px linkage data.
- Q5126 CMS LCD: Billing and Coding: Bevacizumab and biosimilars CMS LCD
- Q5129 CMS LCD: Billing and Coding: Bevacizumab and biosimilars CMS LCD
- Q5118 CMS LCD: Billing and Coding: Bevacizumab and biosimilars CMS LCD
- J9035 CMS LCD: Billing and Coding: Bevacizumab and biosimilars CMS LCD
- Q5107 CMS LCD: Billing and Coding: Bevacizumab and biosimilars CMS LCD
- Q5160 CMS LCD: Billing and Coding: Bevacizumab and biosimilars CMS LCD
- 76873 CMS LCD: Billing and Coding: Transrectal Ultrasound CMS LCD
- 76872 CMS LCD: Billing and Coding: Transrectal Ultrasound CMS LCD
Convert C45.1 to ICD-9-CM
Per CMS General Equivalence Mappings (GEMs), useful for legacy data review and historical claim analysis.
| ICD-10 | ICD-9 | Mapping Flags |
|---|---|---|
| C45.1 | 1588 | 10000 |
Flags format (5 digits): Approximate · No Map · Combination · Scenario · Choice List. Source: CMS 2017 GEMs (final version).
Codes Adjacent To C45.1
Other codes in section C45-C49 (Malignant neoplasms of mesothelial and soft tissue).
ICD-10 C45.1, Billing FAQ
Is ICD-10 code C45.1 billable? +
Yes, C45.1 is a billable ICD-10-CM code that can appear as a primary or secondary diagnosis on claims.
What other names or terms map to C45.1? +
ICD-10 C45.1 includes: Mesothelioma of cul-de-sac; Mesothelioma of mesentery; Mesothelioma of mesocolon, and 2 more clinical synonyms.
What codes are Type 1 Excludes for C45.1? +
Type 1 Excludes (never code together with C45.1): other malignant neoplasm of soft tissue of peritoneum (C48.-)
Does C45.1 affect Medicare Advantage HCC risk adjustment? +
Yes. C45.1 maps to CMS-HCC v28 category 9. Capture this diagnosis annually for accurate Medicare Advantage risk score.
Is C45.1 a CC or MCC for inpatient DRG? +
Yes, this code is designated as CC. Documenting as a secondary diagnosis on inpatient claims can shift the DRG to a higher-weighted category.
What CPT codes are commonly billed with C45.1? +
Procedures frequently paired with C45.1 include: Q5126, Q5129, Q5118, J9035, Q5107.
What ICD-9 codes does C45.1 map to? +
Per CMS GEMs, C45.1 maps to ICD-9 codes: 1588. Useful for legacy data review and historical claim analysis.
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Reviewed by the PayerReady Medical Coding Team
Verified against the CMS 2026 code set on May 31, 2026.
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