M31.19 classifies thrombotic microangiopathies that don't fall under hematopoietic stem cell transplantation-associated TMA (M31.11) or the unspecified category (M31.10) — most notably serving as the designated code for thrombotic thrombocytopenic purpura (TTP).

Documentation tips

What should appear in the chart to support M31.19.

Source · Editorial brief grounded in 6 cited references ↓

• Provider must name the specific TMA variant — 'TTP' or 'thrombotic thrombocytopenic purpura' in the note locks in M31.19 and prevents a drop to the unspecified M31.10.
• If the TMA is transplant-related, the note must explicitly state the HSCT connection — that routes to M31.11, not M31.19.
• Document any organ manifestations (renal, neurological) as separate diagnoses; they are not integral to M31.19 and should be coded additionally.
• Record relevant lab findings supporting TMA — microangiopathic hemolytic anemia, thrombocytopenia, ADAMTS13 activity level — to substantiate medical necessity for associated procedures and treatments.
• Avoid vague terms like 'thrombotic disorder' or 'microangiopathy NOS' in the impression; these force the coder to M31.10 (unspecified) and may trigger payer scrutiny.

Common coding pitfalls

The recurring mistakes coders make with M31.19 and adjacent codes.

Source · Editorial brief grounded in CDC ICD-10-CM tabular guidance, AAOS coding references, and cited references ↓

• Assigning the non-billable parent code M31.1 instead of drilling down to M31.10, M31.11, or M31.19 — M31.1 is a header code and will be rejected on claims.
• Using M31.10 (unspecified) when the provider has explicitly documented TTP — M31.19 is the correct and more specific code in that scenario.
• Routing TTP to a hematology chapter code when the provider uses a general purpura term; the ICD-10-CM Tabular List cross-references thrombotic thrombocytopenic purpura directly to M31.19, not to a D-chapter code.
• Failing to add manifestation codes for secondary organ involvement (e.g., acute kidney injury) when documented — M31.19 alone does not capture those complications.
• Confusing M31.19 with purpura codes in the D89 range (e.g., benign hypergammaglobulinemic purpura D89.0, cryoglobulinemic purpura D89.1) — these are explicitly excluded from the M31 category.

Clinical context

Source · Editorial summary grounded in 6 cited references ↓

Inclusion & exclusion notes

Per the official ICD-10-CM Tabular List.

Source · CDC ICD-10-CM Official Tabular List · 2026

Sibling codes

Other billable codes under M31.1 (laterality / anatomic variants).