E80.21
BillableAcute intermittent (hepatic) porphyria
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is E80.21 an HCC code?
Yes. E80.21 maps to Glycogen/Amino-Acid/Other Metabolic Disorders under the CMS-HCC V28 risk adjustment model (and Other Significant Endocrine and Metabolic Disorders under V24).
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 E80.21
For E80.21 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 E80.21 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
E80.21 is the ICD-10-CM diagnosis code for acute intermittent (hepatic) porphyria. A severe inherited porphyria causing sudden attacks of severe abdominal pain, neurological symptoms, and psychiatric manifestations. E80.21 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 CMS-HCC V28 risk adjustment model, E80.21 maps to Glycogen/Amino-Acid/Other Metabolic Disorders (HCC 50) with a community, non-dual, aged base RAF weight of 0.289. Under the older CMS-HCC V24 model, E80.21 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.
Document acute attack episodes separately from the chronic condition. Because E80.21 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 E80.21 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Document acute attack episodes separately from the chronic condition
- •Code associated neurological or psychiatric complications that occur during attacks
Clinical Significance
Acute intermittent porphyria (AIP) is the most common acute hepatic porphyria, caused by deficiency of porphobilinogen deaminase (HMBS). It presents with neurovisceral crises including severe abdominal pain, neuropsychiatric symptoms, autonomic dysfunction, and potentially life-threatening hyponatremia, typically triggered by drugs, hormones, fasting, or stress.
Documentation Requirements
- ✓Provider diagnosis of acute intermittent porphyria
- ✓Elevated urine porphobilinogen (PBG) and aminolevulinic acid (ALA) during acute attacks
- ✓HMBS/PBGD enzyme activity or HMBS gene mutation testing
- ✓Attack history: frequency, triggers (medications, hormones, fasting), severity
- ✓List of safe vs. unsafe medications maintained in the record
- ✓Acute management: IV hemin (Panhematin), glucose loading, pain management
- ✓Current preventive measures (GnRH agonist for menstrual-triggered attacks)
Commonly Confused Codes
- •E80.1 — Porphyria cutanea tarda: cutaneous porphyria without acute neurovisceral attacks
- •E80.29 — Other porphyria: includes variegate porphyria and hereditary coproporphyria which can also cause acute attacks but have skin involvement too
- •E80.20 — Unspecified porphyria: avoid when AIP is specifically diagnosed
- •R10.9 — Unspecified abdominal pain: AIP attacks may be misdiagnosed as surgical abdomen