E70.40
BillableDisorders of histidine metabolism, unspecified
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is E70.40 an HCC code?
Yes. E70.40 maps to Other Significant Endocrine and Metabolic Disorders under the V24 model but is not retained in V28.
HCC Category Mapping
RAF weights shown are the community, non-dual, aged base weights from the CMS risk adjustment model file. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.
MEAT Criteria for E70.40
For E70.40 to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically — it has to be re-documented and supported each calendar year.
- MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
- EEvaluate: test results, medication response, or physical findings reviewed by the provider
- AAssess: explicit mention in the assessment or plan with acknowledgment of status
- TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis
Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed E70.40 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
E70.40 is the ICD-10-CM diagnosis code for disorders of histidine metabolism, unspecified. A metabolic disorder affecting the breakdown of histidine (an amino acid) when the specific type is not identified. E70.40 sits in the ICD-10-CM chapter for endocrine, nutritional and metabolic diseases (e00-e89), within the section covering metabolic disorders (e70-e88).
Under the older CMS-HCC V24 model, E70.40 maps to Other Significant Endocrine and Metabolic Disorders (HCC 23) with a community, non-dual, aged base RAF weight of 0.230. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.
This is an unspecified code; use only when the specific histidine metabolism disorder cannot be determined. Because E70.40 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.
HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for E70.40 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This is an unspecified code; use only when the specific histidine metabolism disorder cannot be determined
- •Query documentation to determine if histidinemia or other specified disorder of histidine metabolism is present
Clinical Significance
Unspecified disorder of histidine metabolism indicates an identified abnormality in how the body processes the amino acid histidine, but the specific condition has not been determined. Histidine metabolism disorders are generally benign, with histidinemia being the most common and typically asymptomatic, but some variants may be associated with intellectual disability or speech delays, making accurate diagnosis important for prognostic counseling.
Documentation Requirements
- ✓Documentation should include elevated histidine levels on amino acid analysis, any clinical manifestations present, newborn screening results if applicable, and the plan for further diagnostic evaluation.
- ✓The provider should document why the specific disorder cannot be determined and note any developmental assessments performed.
- ✓Family history of metabolic disorders should be recorded.
Commonly Confused Codes
- •E70.41 (Histidinemia) is the specific code when that diagnosis is confirmed.
- •E70.49 (Other disorders of histidine metabolism) covers specific non-histidinemia variants.
- •E70.9 (Disorder of aromatic amino-acid metabolism, unspecified) is a broader category.
- •E70.0 (Classical phenylketonuria) and E70.1 (Other hyperphenylalaninemias) involve a different amino acid.