M79.81 identifies a spontaneous or pathologic localized blood collection within soft tissue or muscle that has no traumatic cause — including nontraumatic seroma of muscle and soft tissue.
Verified May 8, 2026 · 4 sources ↓
- Status
- Billable
- Chapter
- 13
- Related CPT
- 8
- Region
- General
Documentation tips
What should appear in the chart to support M79.81.
Source · Editorial brief grounded in 4 cited references ↓
- Explicitly document absence of traumatic mechanism — phrases like 'spontaneous hematoma' or 'hematoma without trauma' lock in M79.81 and prevent a payer query about injury coding.
- State the anatomic location by name (e.g., anterior thigh, posterior calf, deltoid region) even though M79.81 has no laterality sub-codes — supports medical necessity and CPT site-specific I&D code selection.
- If anticoagulation, thrombocytopenia, or a coagulopathy contributed, document the causal condition separately so it can be sequenced as the principal diagnosis when appropriate.
- Distinguish hematoma from seroma in the note if clinically feasible; both map to M79.81 per the Applicable To notation, but the distinction matters for CPT procedure coding and authorization.
- Document prior conservative management (compression, rest, monitoring) if an I&D procedure is planned — this establishes medical necessity for the intervention.
Related CPT procedures
Procedure codes commonly billed with M79.81. Linking the right diagnosis to the right procedure is what establishes medical necessity.
Source · CMS LCDs · AAOS specialty guidance · claims-pattern analysis
Common coding pitfalls
The recurring mistakes coders make with M79.81 and adjacent codes.
Source · Editorial brief grounded in CDC ICD-10-CM tabular guidance, AAOS coding references, and cited references ↓
- Using M79.81 for a post-traumatic hematoma: if the record documents any injury mechanism, use the appropriate S-code with 7th-character A (initial), D (subsequent), or S (sequela) instead.
- Defaulting to M79.81 for a postprocedural hematoma: complications of surgery or other procedures require a complication code from the T80–T88 range as the primary code, not M79.81.
- Failing to code the underlying cause — such as a coagulopathy or anticoagulant adverse effect — when it drives the encounter; M79.81 should then be a secondary code, not the first-listed diagnosis.
- Selecting a site-nonspecific I&D CPT code (10140) when a site-specific code (e.g., 27603 for leg/ankle) is available and better supported by the documented anatomic location.
- Confusing M79.81 with M79.89 (Other specified soft tissue disorders): M79.81 is the specific billable code for nontraumatic hematoma/seroma; M79.89 is a catch-all and should not be used when M79.81 applies.
Clinical context
Source · Editorial summary grounded in 4 cited references ↓
Use M79.81 when the provider documents a soft tissue or intramuscular hematoma that arose without a precipitating injury — for example, a hematoma secondary to anticoagulation therapy, a bleeding diathesis, or spontaneous vascular rupture into muscle. The absence of trauma is the defining criterion; if a traumatic mechanism is documented, an S-code with the appropriate 7th-character extension is required instead.
The ICD-10-CM Tabular List includes two 'Applicable To' notes under M79.81: nontraumatic hematoma of muscle, and nontraumatic seroma of muscle and soft tissue. Both conditions map here, so a documented nontraumatic seroma does not need a separate code. M79.81 has no laterality sub-codes; if payer policies or clinical context require body-region specificity, support it in documentation even though the code itself is site-nonspecific.
M79.81 sits under parent M79.8 (Other specified soft tissue disorders) in Chapter 13. When the hematoma is a postprocedural complication rather than a spontaneous event, consider complication codes in the T80–T88 range before defaulting to M79.81. If a hemophilia or other coagulopathy is the underlying driver, code the primary condition first and use M79.81 as an additional code per instructional notes.
Inclusion & exclusion notes
Per the official ICD-10-CM Tabular List.
Source · CDC ICD-10-CM Official Tabular List · 2026
Includes
- Nontraumatic hematoma of muscle
- Nontraumatic seroma of muscle and soft tissue
Sibling codes
Other billable codes under M79.8 (laterality / anatomic variants).
Frequently asked questions
Source · Generated from the editorial pipeline, verified against 4 cited references ↓
01Can I use M79.81 for a hematoma that developed after surgery?
02Does M79.81 require a laterality modifier or additional site-specific code?
03Does a nontraumatic seroma get its own code, or does it also map to M79.81?
04What if the hematoma is caused by anticoagulant therapy — is M79.81 still correct?
05Which CPT code should I pair with M79.81 for an incision and drainage?
06Is M79.81 valid for both muscle hematomas and subcutaneous soft tissue hematomas?
07What distinguishes M79.81 from a traumatic hematoma S-code?
Sources & references
Editorial content was developed using the following public sources. Last verified May 8, 2026.
- 01CDC ICD-10-CM Tabular List 2026 (FY2026, effective October 1, 2025)
- 02icd10data.comhttps://www.icd10data.com/ICD10CM/Codes/M00-M99/M70-M79/M79-/M79.81
- 03mdclarity.comhttps://www.mdclarity.com/icd-codes/m79-81
- 04aapc.comhttps://www.aapc.com/codes/icd-10-codes/M79.81
Mira AI Scribe
Mira's AI scribe captures the absence of trauma, anatomic site, suspected etiology (e.g., anticoagulation, coagulopathy), imaging confirmation (ultrasound or MRI findings of fluid/blood collection), and any prior conservative management from the encounter note. Capturing these elements prevents downcoding to M79.89, avoids payer queries about missing injury mechanism, and ensures the correct site-specific I&D CPT code is paired at claim submission.
See how Mira captures M79.81 documentation