M31.10 identifies thrombotic microangiopathy (TMA) when the specific subtype or underlying cause has not been documented or determined. It is the unspecified fallback within the M31.1 category when neither HSCT-TMA (M31.11) nor another defined TMA variant (M31.19) applies.
Verified May 8, 2026 · 5 sources ↓
- Status
- Billable
- Chapter
- 13
- Related CPT
- 0
- Region
- General
Documentation tips
What should appear in the chart to support M31.10.
Source · Editorial brief grounded in 5 cited references ↓
- Document the clinical basis for TMA diagnosis: thrombocytopenia, microangiopathic hemolytic anemia, and end-organ involvement should appear in the note to support the diagnosis.
- Record ADAMTS13 activity results when available — severely reduced activity points toward TTP and may support a more specific code or affect treatment documentation.
- If the TMA is associated with a systemic connective tissue disorder (e.g., SLE, systemic sclerosis), code that underlying condition first and list M31.10 as an additional diagnosis.
- Specify any known etiology in the assessment: drug-induced, complement-mediated, infection-associated, or transplant-related subtypes each have more precise codes than M31.10.
- Note whether the encounter is for initial workup, ongoing management, or follow-up — clinical context supports medical necessity even though M-codes carry no 7th-character encounter modifier.
Common coding pitfalls
The recurring mistakes coders make with M31.10 and adjacent codes.
Source · Editorial brief grounded in CDC ICD-10-CM tabular guidance, AAOS coding references, and cited references ↓
- Billing M31.1 (the non-billable parent) instead of M31.10 — M31.1 is not valid for claim submission; always code to the full 5-character specificity.
- Using M31.10 when the record documents HSCT as the trigger — that maps to M31.11, not the unspecified code.
- Defaulting to M31.10 when the provider documents a distinct TMA subtype that qualifies as M31.19 (Other thrombotic microangiopathy), leaving specificity on the table.
- Omitting the underlying systemic autoimmune condition as a primary diagnosis when TMA is a manifestation — sequencing error can trigger medical necessity denials.
- Confusing TMA with disseminated intravascular coagulation (DIC), which codes to D65 — verify the clinical diagnosis before selecting M31.10.
Clinical context
Source · Editorial summary grounded in 5 cited references ↓
Thrombotic microangiopathy is a syndrome characterized by microvascular thrombosis, thrombocytopenia, and hemolytic anemia, with clinical presentations ranging from thrombotic thrombocytopenic purpura (TTP) to hemolytic uremic syndrome (HUS) and transplant-associated variants. M31.10 sits under the M31.1 (Thrombotic microangiopathy) parent category within the necrotizing vasculopathies block (M30–M36) of Chapter 13.
Use M31.10 only when the provider documents TMA without specifying the etiology or subtype. If the record documents hematopoietic stem cell transplantation as the precipitating cause, use M31.11 (HSCT-TMA) instead. If a distinct non-HSCT subtype is identified — such as drug-induced TMA, complement-mediated TMA, or infection-associated TMA — and it doesn't map to M31.11, M31.19 (Other thrombotic microangiopathy) is the correct pick.
This code most commonly surfaces in rheumatology, nephrology, and hematology encounters, but orthopedic and connective tissue practices may encounter it when TMA complicates a systemic autoimmune condition (e.g., systemic lupus erythematosus, systemic sclerosis) managed in an MSK setting. The M30–M36 section's Excludes1 notation excludes single-organ autoimmune disease, so confirm the condition is systemic before applying any code in this range.
Sibling codes
Other billable codes under M31.1 (laterality / anatomic variants).
Frequently asked questions
Source · Generated from the editorial pipeline, verified against 5 cited references ↓
01When should I use M31.10 versus M31.19?
02Is M31.1 billable as a standalone claim code?
03Can M31.10 be used for thrombotic thrombocytopenic purpura (TTP)?
04Does M31.10 require a 7th-character extension?
05How should I sequence M31.10 when TMA complicates a systemic autoimmune disease?
06Is there an Excludes1 or Excludes2 note I need to watch for under M31.10?
07When was M31.10 introduced as a distinct billable code?
Sources & references
Editorial content was developed using the following public sources. Last verified May 8, 2026.
- 01CDC ICD-10-CM Tabular List 2026 (effective Oct 1, 2025)
- 02icd10data.comhttps://www.icd10data.com/ICD10CM/Codes/M00-M99/M30-M36/M31-/M31.10
- 03icd10data.comhttps://www.icd10data.com/ICD10CM/Codes/M00-M99/M30-M36/M31-/M31.1
- 04aapc.comhttps://www.aapc.com/codes/icd-10-codes/M31.10
- 05aapc.comhttps://www.aapc.com/codes/icd-10-codes/M31.1
Mira AI Scribe
The Mira AI Scribe captures lab findings (platelet count, LDH, haptoglobin, peripheral smear for schistocytes), ADAMTS13 activity if ordered, documented end-organ involvement, and the provider's explicit TMA diagnosis from the assessment. It also flags whether a specific subtype or precipitating cause is named, preventing a fallback to the unspecified M31.10 when a more precise code (M31.11 or M31.19) is supportable — and avoiding the non-billable M31.1 parent code on the claim.
See how Mira captures M31.10 documentation