The World Health Organization (WHO) defines malnutrition as “deficiencies, excesses, or imbalances in a person’s intake of energy and/or nutrients.” Malnutrition leads to various health problems and contributes to mortality, especially among children. Overweight and obesity occur when abnormal or excessive fat accumulation poses a risk to health. While proper nutrition is vital for disease prevention, overall well-being, and longevity, excess weight significantly increases the risk of chronic conditions such as cardiovascular disease, type 2 diabetes, and certain cancers. ICD-10 offers codes and guidelines to report these conditions. However, malnutrition, obesity, and BMI coding can be challenging due to nuanced documentation, evolving guidelines, and the need for precise clinical detail.
Globally, malnutrition – in both its extremes of undernutrition and obesity – affects millions of people. The US has high rates of both malnutrition and obesity, but the most significant issue is obesity. New CDC population data from 2023 show that in 23 states more than one in three adults (35%) has obesity. Both conditions require detailed documentation in patient records, including physical exams, patient history, and treatment plans. Relying on AI-driven medical coding services can help providers navigate billing and coding complexities with ease. By analyzing clinical notes in real time, AI ensures that the correct ICD-10 codes, obesity and malnutrition severity levels, and BMI classifications are captured consistently.
This post takes you through official guidelines for provider documentation requirements and best practices for coding BMI, malnutrition, and obesity in outpatient settings:
Malnutrition, Obesity, and BMI Coding and Documentation Guidelines
Malnutrition
Malnutrition codes fall within the E40-E46 range. The severity is often categorized, and the specific codes used depend on clinical indicators.
- E40 – Kwashiorkor (nutritional edema with dyspigmentation of skin and hair)
- E41 – Nutritional marasmus (severe energy deficiency) (rarely used in the U.S.)
- E42 – Marasmic kwashiorkor (intermediate form of severe protein-calorie malnutrition)
- E43 – Unspecified severe protein-calorie malnutrition
- E44.0 – Moderate protein-calorie malnutrition
- E44.1 – Mild protein-calorie malnutrition
- E46 – Unspecified protein-calorie malnutrition
- E64 – Sequelae of malnutrition and other nutritional deficiencies
For patients who are simply underweight (BMI < 18.5) without a specific malnutrition diagnosis, the code is R63.6.
To note:
- E40 – Kwashiorkor refers to severe malnutrition with nutritional edema and dyspigmentation of skin and hair. It is a rare occurrence in the U.S.
- E41 refers to nutritional marasmus, a form of malnutrition characterized by consumption of inadequate amounts of both protein and calories, leading to an energy deficit in the body. Common symptoms include dehydration, chronic diarrhea, and stomach shrinkage. This severe malnutrition type occurs in young children and infants.
- E42 signifies severe protein-calorie malnutrition with signs of both kwashiorkor and marasmus. This is an intermediate form of severe malnutrition.
- E43 is unspecified severe malnutrition and used to report severe malnutrition or starvation edema.
- E44.0 (moderate malnutrition), E44.1 (mild malnutrition), and E46 (malnutrition, unspecified) are categorized as complication/comorbid conditions (CCs).
Severe malnutrition diagnosis codes are for major complications/comorbid conditions (MCCs) and are scrutinized by commercial and government payers. When reporting a severe malnutrition ICD-10 code, documentation must support muscle wasting with clinical indicators to avoid a reduction in the assigned Diagnosis-Related Groups (DRGs) (ICD-10 Monitor).
To meet the American Society for Parenteral and Enteral Nutrition (ASPEN) criteria for severe malnutrition in an acute care setting, the Association of Clinical Documentation Integrity Specialists (ACDIS) notes that a patient must show the following symptoms:
- Energy intake: less than () 5 days
- Weight loss (% of body weight):
- >2% in one week; or
- >5% in one month; or
- >7.5% in three months
- Muscle mass loss: moderate
- Body fat loss: moderate
- Edema masking weight loss: moderate to severe
- Reduced grip strength: measurably reduced
Obesity
Obesity is classified into three classes based on severity. Using the correct obesity class code helps support patient access to appropriate services, such as intensive behavioral interventions, lifestyle counseling, or bariatric surgery.
Codes E66.811–E66.813 are highly specific codes (that became effective October 1, 2024) to identify the diagnosed class of obesity:
- E66.811 – Class 1 Obesity: BMI 30.0–34.9,
- E66.812 – Class 2 Obesity: BMI 35.0–39.9
- E66.813 – Class 3 Obesity: BMI ≥ 40.0 (also referred to as severe, morbid, or extreme obesity)
Other common ICD-10 codes for obesity:
- E66.01 – Morbid (severe) obesity due to excess calories
- E66.09 – Other obesity due to excess calories
- E66.1 – Drug-induced obesity
- E66.2 – Morbid (severe) obesity with alveolar hypoventilation (i.e., associated with obesity-hypoventilation syndrome)
- E66.3 – Overweight (less than full obesity)
- E66.89 – Other obesity, not elsewhere classified
- E66.9 – Obesity, unspecified (used when documentation does not specify type or class)
- Z15.2 – Genetic susceptibility to obesity
To note:
- Obesity codes require specific provider documentation to be reported.
- It’s recommended to report both the obesity code and a BMI code (from Z68) when BMI is known, for more precise documentation and to support severity classification (AAPA). BMI codes are often required for quality reporting and performance measurement.
- Avoid using non-billable “root” codes such as E66 (unspecified overweight/obesity) when a more specific code is available.
Body Mass Index
BMI Z-codes are secondary diagnosis codes (Z68.- category) used to support a primary diagnosis of a weight condition (e.g., malnutrition, overweight, or obesity).
Adult BMI Codes (for persons 20 years or older)
These codes are highly specific, covering ranges in 1 kg/m² increments:
- Z68.25-29.9 Body mass index (BMI) 25-29.9
- Z68.30-Z68.39 Body mass index (BMI) 30.0-39.9
- Z68.4 Body mass index (BMI) 40 or greater
- Z68.41 Body mass index (BMI) 40.0-44.9
- Z68.42 Body mass index (BMI) 45.0-49.9
- Z68.43 Body mass index (BMI) 50-59.9
- Z68.44 Body mass index (BMI) 60.0-69.9
- Z68.45 Body mass index (BMI) 70 or greater
- Z68.1 – BMI 19.9 or less, adult (underweight)
Pediatric BMI Codes (for persons ages 2 to 19)
New pediatric BMI codes based on percentiles were added for 2025 to provide greater detail for different weight categories. These codes include:
- Z68.51 – BMI pediatric, less than 5th percentile (underweight)
- Z68.52 – BMI pediatric, 5th percentile to less than 85th percentile
- Z68.53 – BMI pediatric, 85th percentile to less than 95th percentile (overweight)
- Z68.54 (obesity, ≥95th percentile) – Z68.56 (severe obesity) – These codes cover pediatric obesity class equivalents based on percentiles relative to the 95th percentile
In the MS-DRG system, a BMI below 20 or above 40 is recognized as a complication/comorbidity (CC). This classification can impact inpatient reimbursement by reflecting the added clinical complexity associated with caring for these patients.
ICD-10-CM coding tips for capturing obesity and BMI scores:
- Document height and weight clearly so that BMI can be calculated accurately.
- The provider should record the BMI value explicitly in the medical record as well as the related diagnosis (e.g., obesity, overweight, underweight), because BMI alone cannot be coded as a clinical condition.
- Use the most recent BMI measurement (ideally captured during the current encounter) to support coding and quality reporting.
- Document BMI trends when clinically relevant, especially when monitoring weight management, chronic disease progression, or treatment response.
- For pediatric patients, note height, weight, and percentile-based BMI to ensure age-appropriate coding.
- Include the clinical significance of abnormal BMI when appropriate (e.g., nutritional risk, comorbidity impact, or need for intervention).
- Ensure consistency between BMI and the obesity class (Class 1, 2, or 3) in provider documentation.
- For HCC reporting, morbid obesity (E66.01) is an HCC, and its classification can be supported by the documented BMI.
- Do not code BMI for obstetric (OB) patients; BMI codes are not applied in pregnancy-related encounters.
- Do not assign a diagnosis code based solely on BMI. Coding is not driven by clinical criteria or numerical thresholds but by the provider’s documented diagnosis related to weight.
Coding Clinic clarifies that when “overweight” is documented, it may be assigned a secondary diagnosis only if it meets the standard criteria: clinical evaluation, therapeutic treatment, diagnostic testing, increased nursing care or monitoring, or contribution to an extended length of stay.
Improve Malnutrition, Obesity, and BMI Coding with AI Support
Accurate coding of malnutrition, obesity, and BMI is essential for good documentation, quality reporting, HCC capture, and correct reimbursement. Providers must clearly document the weight-related diagnosis, and BMI values should be recorded consistently and tied to the patient’s clinical picture. Because nutritional status coding can be complex, tools that improve accuracy and reduce missed details are especially helpful.
AI medical coding solutions support these requirements by spotting missing documentation, catching inconsistencies between BMI and the documented diagnosis, and checking whether conditions meet secondary diagnosis criteria. By helping coders work more accurately and efficiently, an AI-powered medical coding company can improve documentation quality, reflect true patient acuity, and strengthen revenue integrity across healthcare settings.
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