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.

Which HCC does E66.2 map to under V28?

E66.2 maps to CMS-HCC V28 HCC 48 (Morbid Obesity). The category numbers, labels, and conditions come from the CMS-HCC V28 model file for payment year 2026.

What documentation supports 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. For E66.2, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule. See the MEAT criteria checklist at /meat-criteria for what Monitor, Evaluate, Assess, or Treat looks like in a note. One mnemonic element does not establish that a diagnosis is reportable.

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

E66.2 maps to CMS-HCC V28 48. A source-labeled RAF reference is available. Confirm the documented diagnosis and applicable coding requirements. MEAT criteria · RAF Calculator · HCC Buddy coding tools

ICD-10-CM Code View

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Code lookupE66.2

Effective 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

Overview Risk Models Code Book Documentation Audit Notes Edition comparison

CMS-HCC V28

Mapped

HCC 48

Morbid Obesity

Code-level coefficient reference

CMS-HCC V24

Historical

Not used for standard CY2026 Medicare Advantage payment. Select a historical period to review V24.

Not used for CY2026 payment

ACA/HHS

N/A

—

Not risk-adjusted for this model/period.

Not mapped

ESRD/PACE

Mapped

HCC 22

Morbid Obesity

Code-level coefficient reference

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)Inherited from E66
lipomatosis dolorosa [Dercum] (E88.2)Inherited from E66
lipomatosis NOS (E88.2)Inherited from E66
Prader-Willi syndrome (Q87.11)Inherited from E66

Related Codes

Official

E66.0Obesity due to excess calories E66.1Drug-induced obesity E66.3Overweight E66.8Other obesity E66.9Obesity, unspecified

Includes

Official

No Includes notes are included in this display for E66.2. Check the code and parent instructions in the Code Book.

Excludes 1

Official

No Excludes 1 notes are included in this display for E66.2. Check the code and parent instructions in the Code Book.

Code First

Official

obesity complicating pregnancy, childbirth and the puerperium, if applicable (O99.21-)Inherited from E66

Use Additional

Official

code to identify body mass index (BMI), if known, for adults (Z68.1-Z68.45) or pediatrics (Z68.5-)Inherited from E66

Code Also

Official

No Code Also instructions are included in this display for E66.2. Check the code and parent instructions in the Code Book.

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 HCC 48, Morbid Obesity under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.186. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes. 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 reference coefficient: 0.186
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 48, Morbid Obesity

0.186

ESRDHCC 22, Morbid Obesity

Not separately weighted

These are source-labeled model coefficients, not member totals. A category may still be removed by hierarchy or model cleanup rules. 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 context, hierarchy and cleanup rules, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains available for historical review.

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

MEAT review for E66.2

For E66.2, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule.

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

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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 source-labeled community, non-dual, aged reference coefficient of 0.186. No V24 mapping is shown for E66.2; use the applicable model and payment year when reviewing the V28 mapping. For CY2026 non-PACE Medicare Advantage, CMS uses 100% of the 2024 CMS-HCC model (V28). PACE uses a separate model blend. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes.

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. For E66.2, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule. 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, source-labeled coefficient references, 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.
•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.