What is ICD-10 code E66.2?

E66.2 is the ICD-10-CM diagnosis code for Morbid (severe) obesity with alveolar hypoventilation. It belongs to the ICD-10-CM chapter for endocrine, nutritional and metabolic diseases (e00-e89). E66.2 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. E66.2 is part of the FY2026 ICD-10-CM code set published by the CMS National Center for Health Statistics and used on Medicare, Medicaid, and commercial claims in the United States.

Yes. E66.2 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. E66.2 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

What is the V28 vs V24 difference for E66.2?

CMS phased in the V28 risk adjustment model over payment years 2024 (33%), 2025 (67%), and 2026 (100%), replacing V24. V28 consolidates HCC categories, removes some lower-acuity conditions, and recalibrates RAF weights across the entire model. For E66.2, V28 maps to Morbid Obesity at RAF 0.186 while V24 mapped to Morbid Obesity at RAF 0.250. Both models can still appear in legacy data and in payer-specific lookback periods.

What should coders know when reporting E66.2?

Morbid obesity with alveolar hypoventilation (obesity hypoventilation syndrome, Pickwickian syndrome), requires documentation of obesity plus hypoventilation with daytime hypercapnia. A sleep study and ABG abnormalities support the diagnosis. Distinct from obesity with OSA alone, OSA is captured separately (G47.33) and does not meet the hypoventilation criterion. Pickwickian requires hypercapnia, not just apnea. V28 HCC 48 at RAF 0.186. One of the highest-specificity morbid obesity codes; defensible in audit when the ABG and sleep study are in the chart. Because E66.2 maps to a payment HCC, the documentation must also satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's risk adjustment score.

2026 ICD-10-CM E66.2: Morbid (severe) obesity

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Code lookupE66.2Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Endocrine, nutritional and metabolic diseases (E00-E89) / Overweight, obesity and other hyperalimentation (E65-E68)

E66.2

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

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.

Buddy Insight

CMS-HCC V28

Mapped

HCC 48

Morbid Obesity

RAF 0.186

CMS-HCC V24

Mapped

HCC 22

Morbid Obesity

RAF 0.250

ACA/HHS

N/A

—

Not risk-adjusted for this model/period.

Not mapped

ESRD/PACE

Mapped

HCC 22

Morbid Obesity

RAF 0.081

RXHCC

N/A

—

Not risk-adjusted for this model/period.

Not mapped

Code Book Path

Official

E66Overweight and obesity

E66.2Morbid (severe) obesity with alveolar hypoventilation

Inclusion Terms

Official

Obesity hypoventilation syndrome (OHS)
Pickwickian syndrome

Excludes 2

Official

adiposogenital dystrophy (E23.6)
lipomatosis dolorosa [Dercum] (E88.2)
lipomatosis NOS (E88.2)
Prader-Willi syndrome (Q87.11)

Related Child Codes

Official

E66.0Obesity due to excess calories

E66.1Drug-induced obesity

E66.3Overweight

E66.8Other obesity

E66.9Obesity, unspecified

Includes

Official

ICD-10-CM does not list Includes notes for E66.2 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for E66.2 in this effective period.

Code First

Official

obesity complicating pregnancy, childbirth and the puerperium, if applicable (O99.21-)

Use Additional

Official

code to identify body mass index (BMI), if known, for adults (Z68.1-Z68.45) or pediatrics (Z68.5-)

Code Also

Official

ICD-10-CM does not list Code Also instructions for E66.2 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

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.

MEAT Support

HCC Buddy guidance

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.

Audit Caution

HCC Buddy guidance

This combination code captures both the morbid obesity and the hypoventilation, so do not assign a separate E66.01 code.

However, obstructive sleep apnea (G47.3x) may coexist and should be coded separately if documented as a distinct condition.

Ensure arterial blood gas evidence supports the hypoventilation diagnosis rather than assuming it from symptoms alone.

Distinguish from pure obstructive sleep apnea without daytime hypercapnia.

Common Mistakes

HCC Buddy guidance

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.

Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →

Is E66.2 an HCC code?

Yes. E66.2 (Morbid (severe) obesity with alveolar hypoventilation) maps to Morbid Obesity under the CMS-HCC V28 risk adjustment model (and Morbid Obesity under V24), with a community non-dual aged RAF of 0.186. It is billable for payment year 2026.

Coder answer: E66.2 is billable and maps to V28 HCC 48, Morbid Obesity. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code: E66.2
Description: Morbid (severe) obesity with alveolar hypoventilation
HCC (V28): HCC 48 — Morbid Obesity
RAF: 0.186
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 48, Morbid Obesity

0.186

V24HCC 22, Morbid Obesity

0.250

ESRDHCC 22, Morbid Obesity

0.081

Each model's RAF is its CMS base weight for that model's standard population, so weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. 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.

Work E66.2 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

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.

Coder workflow notes

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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 0.186. 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.

Morbid obesity with alveolar hypoventilation (obesity hypoventilation syndrome, Pickwickian syndrome), requires documentation of obesity plus hypoventilation with daytime hypercapnia. A sleep study and ABG abnormalities support the diagnosis. 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

•Morbid obesity with alveolar hypoventilation (obesity hypoventilation syndrome, Pickwickian syndrome), requires documentation of obesity plus hypoventilation with daytime hypercapnia. A sleep study and ABG abnormalities support the diagnosis.
•Distinct from obesity with OSA alone, OSA is captured separately (G47.33) and does not meet the hypoventilation criterion. Pickwickian requires hypercapnia, not just apnea.
•V28 HCC 48 at RAF 0.186. One of the highest-specificity morbid obesity codes; defensible in audit when the ABG and sleep study are in the chart.

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.