E66.2
BillableMorbid (severe) obesity with alveolar hypoventilation
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is E66.2 an HCC code?
Yes. E66.2 maps to Morbid Obesity under the CMS-HCC V28 risk adjustment model (and Morbid Obesity 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 E66.2
For E66.2 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 E66.2 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
E66.2 is the ICD-10-CM diagnosis code for morbid (severe) obesity with alveolar hypoventilation. This condition describes severe obesity that is so significant it causes the person to have shallow breathing and inadequate oxygen intake, often called Pickwickian syndrome. The excess weight physically restricts the lungs' ability to expand fully, leading to respiratory problems. E66.2 sits in the ICD-10-CM chapter for endocrine, nutritional and metabolic diseases (e00-e89), within the section covering overweight, obesity and other hyperalimentation (e65-e68).
Under the CMS-HCC V28 risk adjustment model, E66.2 maps to Morbid Obesity (HCC 48) with a community, non-dual, aged base RAF weight of 0.226. Under the older V24 model, E66.2 mapped to the same category but with a base RAF weight of 0.250 — V28 recalibrated weights across the entire model. 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.
Always verify that both the morbid obesity AND alveolar hypoventilation are documented by the physician before assigning this code; do not assume one causes the other without explicit documentation. Because E66.2 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 E66.2 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Always verify that both the morbid obesity AND alveolar hypoventilation are documented by the physician before assigning this code; do not assume one causes the other without explicit documentation
- •This code includes the obesity component, so do not assign an additional obesity code (E66.0 or E66.1); however, you may need to add a separate respiratory code (such as R06.02 for shortness of breath) if the hypoventilation is documented as a distinct clinical finding
Clinical Significance
Morbid obesity with alveolar hypoventilation, also known as Obesity Hypoventilation Syndrome or Pickwickian Syndrome, is a serious condition where extreme obesity mechanically restricts lung expansion, leading to chronic hypoventilation with daytime hypercapnia and hypoxemia. This condition carries high mortality risk from respiratory failure, pulmonary hypertension, and cor pulmonale, and often requires nocturnal positive airway pressure therapy or invasive ventilation.
Documentation Requirements
- ✓Documentation must include both the morbid obesity diagnosis (with body mass index) and objective evidence of alveolar hypoventilation including arterial blood gas showing daytime hypercapnia (partial pressure of carbon dioxide above 45 mmHg), exclusion of other causes of hypoventilation, and pulmonary function testing.
- ✓Sleep study results, oxygen saturation data, and echocardiographic findings for pulmonary hypertension should be documented.
- ✓Treatment with noninvasive ventilation or other respiratory support should be noted.
Commonly Confused Codes
- •E66.01 (Morbid obesity due to excess calories) does not include the respiratory component.
- •G47.3x (Sleep apnea) is a separate condition that often coexists but is distinct from obesity hypoventilation syndrome.
- •J96.x (Respiratory failure) may be coded additionally for acute decompensation.
- •E66.813 (Obesity, class 3) captures the obesity severity without the respiratory syndrome.
- •R06.89 (Other abnormalities of breathing) is far less specific.