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ICD-10-CM 2027 diagnosis code

M31.1Thrombotic microangiopathy

Not billable — use a more specific code

M31.1 is a header code, so it can't be reported by itself. Choose one of the 3 more specific codes beneath it.

Code last changed in FY2022 (effective October 1, 2021). Source: official FY2027 ICD-10-CM release from CDC/NCHS and CMS. Page updated September 29, 2026. About our data

About M31.1

M31.1 is the ICD-10-CM diagnosis code for thrombotic microangiopathy. It belongs to category M31 (other necrotizing vasculopathies), block M30-M36 (systemic connective tissue disorders) and chapter 13 (diseases of the musculoskeletal system and connective tissue). It is a header code, so it can't be reported by itself; one of its 3 subcodes must be used instead.

Within M31 (other necrotizing vasculopathies), M31.1 is specifically for thrombotic microangiopathy. Related codes cover hypersensitivity angiitis (M31.0), Lethal midline granuloma (M31.2), Wegener's granulomatosis (M31.3), aortic arch syndrome [Takayasu] (M31.4), giant cell arteritis with polymyalgia rheumatica (M31.5), other giant cell arteritis (M31.6), microscopic polyangiitis (M31.7), other specified necrotizing vasculopathies (M31.8) and 1 more.

To report this condition, pick the subcode that matches the documentation: M31.10 (unspecified), M31.11 ([HSCT-TMA]) and M31.19 (microangiopathy).

It has been part of ICD-10-CM since the code set took effect on October 1, 2015, and changed in FY2022 (expanded into subcodes).

Before ICD-10, this condition was coded in ICD-9-CM as 446.6 (thrombotic microangiopathy).

Specific codes under M31.1

Notes that apply from higher levels

Instructions written at a parent level also apply to M31.1.

Broader instructions also apply from M30-M36 Systemic connective tissue disorders and Chapter 13: Diseases of the musculoskeletal system and connective tissue.

ICD-9-CM equivalent

Converter →
  • 446.6Thrombotic microangiopathyexact

From the CMS 2018 General Equivalence Mappings (GEMs), the final GEMs release.

Code history

  1. 2016
  2. 2017
  3. 2018
  4. 2019
  5. 2020
  6. 2021
  7. 2022
  8. 2023
  9. 2024
  10. 2025
  11. 2026
  12. 2027
  • FY2016 (effective 10/1/2015): Added (first year of ICD-10-CM)
  • FY2022 (effective 10/1/2021): Expanded — no longer billable

Common questions about M31.1

Is M31.1 billable?

No. M31.1 is a header code. Report one of its more specific subcodes instead.

What is the ICD-9 code for M31.1?

The CMS General Equivalence Mappings map M31.1 to ICD-9-CM 446.6.