M31.11 identifies thrombotic microangiopathy that arises as a direct complication of hematopoietic stem cell transplantation (HSCT), a distinct clinical entity from other TMA subtypes.

Documentation tips

What should appear in the chart to support M31.11.

Source · Editorial brief grounded in 5 cited references ↓

• Provider must explicitly state the TMA is associated with or caused by hematopoietic stem cell transplantation — 'HSCT-TMA' or 'TA-TMA' in the assessment satisfies this requirement.
• Document all organ systems affected: acute kidney injury, pulmonary involvement (ARDS, diffuse alveolar hemorrhage), and capillary leak syndrome each map to required companion codes under the 'Use Additional' tabular instruction.
• Record the transplant history clearly, including whether allogeneic or autologous HSCT was performed, to support medical necessity and audit defense.
• If TMA type is under evaluation or not yet confirmed as HSCT-related, use M31.10 (unspecified) until etiology is established — do not code M31.11 on suspicion alone.
• Note timing relative to transplant in the clinical note; HSCT-TMA typically presents weeks to months post-transplant and that temporal relationship supports the diagnosis.

Common coding pitfalls

The recurring mistakes coders make with M31.11 and adjacent codes.

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

• Using M31.10 (TMA unspecified) when the record clearly documents HSCT as the cause — M31.11 is required when etiology is established and documented.
• Omitting companion codes for organ dysfunction: the tabular 'Use Additional' instruction is directive, not optional; skipping N17.- or J80 when clinically present results in an incomplete and undercoded claim.
• Applying M31.11 to non-HSCT transplant patients (e.g., solid organ transplant recipients) — those cases belong under M31.19 absent specific guidance linking them to HSCT.
• Backdating M31.11 to encounters prior to October 1, 2021 — the code did not exist before FY2022 and cannot be used for earlier dates of service.
• Confusing M31.11 with thrombotic thrombocytopenic purpura (TTP) or hemolytic uremic syndrome (HUS), which have separate codes and distinct etiologies; HSCT-TMA is a clinically and administratively distinct entity.

Clinical context

Source · Editorial summary grounded in 5 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).