Anorexia Nervosa (ICD-11: 6B80): Complete Coding and Diagnostic Guide

1. Introduction

Anorexia nervosa is a serious eating disorder characterized by significantly low body weight, intense fear of weight gain, and distortion of body image. This disorder represents one of the psychiatric conditions with the highest mortality rate, predominantly affecting adolescents and young adults, although it can occur at any age.

The clinical importance of anorexia nervosa transcends its psychological manifestations, presenting severe medical complications that affect multiple organ systems. Chronic malnutrition can result in cardiovascular, endocrine, gastrointestinal, bone, and neurological alterations that are potentially irreversible. Early identification and appropriate treatment are fundamental to prevent serious complications and improve prognosis.

From an epidemiological perspective, anorexia nervosa presents increasing prevalence in recent decades, particularly among young populations. The disorder predominantly affects individuals of the female sex, although the incidence in men is increasing. Social pressure related to beauty standards, facilitated access to content about restrictive diets, and individual psychological vulnerability contribute to the development of this condition.

Correct coding of anorexia nervosa is critical for multiple aspects of healthcare delivery. It enables appropriate epidemiological monitoring, facilitates resource allocation for specialized treatment, ensures appropriate reimbursement of therapeutic procedures, and contributes to clinical research. Furthermore, accurate documentation is essential for longitudinal follow-up of these patients, who frequently require prolonged multidisciplinary care.

2. Correct ICD-11 Code

Code: 6B80

Description: Anorexia nervosa

Parent category: Feeding or eating disorders

Official definition: Anorexia nervosa is characterized by significantly low body weight for the individual's height, age, and developmental stage that is not due to another health condition or unavailability of food. A commonly used threshold is a body mass index (BMI) below 18.5 kg/m² in adults and BMI-for-age below the 5th percentile in children and adolescents.

Rapid weight loss, such as more than 20% of total body weight over six months, may substitute for this low body weight reference, provided that other diagnostic criteria are met. In children and adolescents, there may be failure to gain weight as expected, based on the individual's developmental trajectory, rather than actual weight loss.

The low body weight is accompanied by a persistent pattern of behaviors to avoid restoration of normal weight. These behaviors include dietary restriction to reduce energy intake, purging behaviors such as self-induced vomiting or misuse of laxatives, and behaviors to increase energy expenditure such as excessive exercise. These behaviors are typically associated with an intense fear of weight gain. Low weight or body shape is a central aspect of the individual's self-evaluation or is erroneously perceived as normal or even excessive.

3. When to Use This Code

Code 6B80 should be used in specific clinical scenarios where all diagnostic criteria are present:

Scenario 1: Adolescent with progressive dietary restriction A 16-year-old female patient presents with BMI of 15.8 kg/m² (below the 5th percentile for age), having lost 18 kg over the past 8 months. She reports obsessively counting calories, avoiding entire food groups (especially carbohydrates and fats), and exercising 2-3 hours daily. She expresses intense fear of "becoming fat" despite evident low weight. Medical evaluation rules out organic causes for weight loss. This case meets all criteria for 6B80.

Scenario 2: Young adult with restrictive-purging pattern A 23-year-old patient with BMI of 16.2 kg/m², presenting with severe dietary restriction combined with episodes of self-induced vomiting after small meals. Uses laxatives daily and exhibits compensatory behavior through excessive exercise. Demonstrates significant body image distortion, perceiving herself as overweight despite evident malnutrition. Code 6B80 is appropriate regardless of the presence of purging behaviors, as long as body weight remains significantly low.

Scenario 3: Child with failure to achieve expected weight gain An 11-year-old child who should be in a phase of accelerated growth has remained stagnant at the same weight for 14 months, resulting in progressively below-expected BMI for age (currently at the 3rd percentile). Presents with elaborate eating rituals, hides food, expresses excessive concern with caloric content, and demonstrates intense anxiety when confronted about eating. This pattern justifies the use of code 6B80, even without absolute weight loss.

Scenario 4: Patient with rapid and significant weight loss A 28-year-old adult who lost 22% of body weight over 5 months through prolonged fasting and extreme restriction. Even though current BMI is 18.7 kg/m² (slightly above the 18.5 threshold), the velocity of weight loss associated with persistent restrictive behaviors and fear of weight restoration justify the diagnosis of anorexia nervosa and the use of code 6B80.

Scenario 5: Patient in partial remission with maintenance of behaviors A 25-year-old individual who achieved BMI of 18.3 kg/m² following hospitalization, but maintains a persistent pattern of dietary restriction, obsessive calorie counting, intense fear of gaining additional weight, and body image distortion. Although weight has partially improved, the persistence of characteristic behaviors and maintenance of borderline weight justify the continuation of code 6B80.

Scenario 6: Athlete with metabolic triad A 19-year-old artistic gymnast with BMI of 16.5 kg/m², amenorrhea for 8 months, and reduced bone density. Presents with intentional dietary restriction to "maintain competitive weight," fear of weight gain that could impair performance, and distortion of body perception. The sports context does not exclude the diagnosis when criteria are present, making code 6B80 appropriate.

4. When NOT to Use This Code

There are specific situations where code 6B80 should not be applied, even when there is low body weight:

Weight loss secondary to general medical conditions: When low body weight results primarily from organic diseases such as neoplasms, inflammatory bowel diseases, hyperthyroidism, decompensated type 1 diabetes mellitus, or chronic infections, the appropriate code is that of the underlying medical condition, not 6B80. The absence of pathological concern with weight/body shape and intentional restrictive behaviors differentiates these conditions.

Avoidant/Restrictive Food Intake Disorder (6B83): When there is food restriction and low body weight, but without body image distortion, fear of weight gain, or concern with body shape. In these cases, food restriction is generally related to lack of interest in eating, sensory avoidance, or fear of aversive consequences (choking, vomiting), not concerns about weight.

Bulimia nervosa (6B81): When there are purging behaviors and concern with weight/body shape, but body weight remains in the normal range or above. Bulimia nervosa is characterized by episodes of binge eating followed by compensatory behaviors, but without the low body weight characteristic of anorexia nervosa.

Malnutrition due to food unavailability: In contexts of food insecurity, extreme poverty, or food scarcity situations, low body weight does not constitute anorexia nervosa even if the individual presents with very low BMI. The fundamental distinction is the intentionality of restrictive behaviors and the specific psychopathology related to weight and body shape.

Psychotic disorders with food-related delusions: When food refusal is related to persecutory delusions (fear of poisoning) or other primary psychotic symptoms, without the specific psychopathology of anorexia nervosa, the appropriate code is that of the underlying psychotic disorder.

Major depression with loss of appetite: Depression can cause significant weight loss through decreased appetite and disinterest in eating, but without the intentional restrictive behaviors, fear of weight gain, or body image distortion characteristic of anorexia nervosa.

5. Step-by-Step Coding Process

Step 1: Assess diagnostic criteria

Diagnostic confirmation of anorexia nervosa requires systematic and comprehensive evaluation. Begin with objective measurement of weight and height to calculate BMI, comparing with appropriate reference values for age and sex. In adults, verify that BMI is below 18.5 kg/m². For children and adolescents, use growth curves to determine whether BMI for age is below the 5th percentile.

Investigate detailed weight history, including maximum weight, minimum weight, rate of weight loss, and methods used to lose weight. Weight loss exceeding 20% of body weight over six months is clinically significant even if current BMI is not extremely low.

Assess eating behaviors through structured clinical interview, investigating restriction patterns (types of foods avoided, caloric intake, fasting periods), purging behaviors (frequency of self-induced vomiting, use of laxatives, diuretics, or other substances), and compensatory exercise (frequency, duration, context).

Explore cognition related to weight and body shape, including fear of weight gain, importance of weight in self-evaluation, perception of body shape, and thoughts about eating. Use validated instruments such as Eating Disorder Examination (EDE) or Eating Attitudes Test (EAT) when available.

Perform complete medical evaluation to identify complications of malnutrition and exclude organic causes of weight loss. Complementary tests should include complete blood count, renal and hepatic function, electrolytes, thyroid function, and electrocardiogram.

Step 2: Verify specifiers

ICD-11 does not specify formal subtypes for anorexia nervosa as DSM-5 does (restrictive vs. purging), but clinical documentation should detail specific characteristics. Record whether purging behaviors (vomiting, laxatives) are present or if the pattern is exclusively restrictive.

Document severity based on current BMI: mild (BMI ≥17), moderate (BMI 16-16.99), severe (BMI 15-15.99), or extreme (BMI <15). In children and adolescents, severity may be based on BMI percentile for age.

Identify the presence of medical complications that increase severity: significant bradycardia, hypotension, hypothermia, electrolyte abnormalities, osteoporosis, prolonged amenorrhea, or other systemic complications.

Record the duration of the disorder, differentiating between single episode, recurrent episode, or chronic course. This information is relevant for treatment planning and prognosis.

Step 3: Differentiate from other codes

6B81 - Bulimia nervosa: The fundamental difference lies in body weight. In bulimia nervosa, weight remains in normal range or above, whereas in anorexia nervosa there is significant low weight. Both may present with purging behaviors, but only anorexia nervosa presents the criterion of significantly low weight. If a patient with anorexia nervosa gains weight and reaches normal range but maintains episodes of binge eating and purging, the diagnosis should be reassessed for bulimia nervosa.

6B82 - Binge eating disorder: Characterized by recurrent episodes of binge eating without regular compensatory behaviors, often resulting in overweight or obesity. The absence of low weight and systematic compensatory behaviors clearly differentiates it from code 6B80.

6B83 - Avoidant/restrictive food intake disorder: Both present with food restriction and low weight, but the motivation is fundamentally different. In avoidant/restrictive food intake disorder, there is no concern with weight or body shape, fear of weight gain, or body image distortion. Restriction relates to disinterest in food, sensory avoidance, or fear of aversive consequences of eating, not concerns about appearance or weight.

Step 4: Necessary documentation

Adequate documentation should include complete checklist: objective anthropometric data (current weight, height, calculated BMI, percentile if applicable), detailed weight history (maximum weight, pre-morbid weight, rate of loss), specific description of eating behaviors (restriction pattern, foods avoided, calorie counting), presence and frequency of purging behaviors or compensatory exercise.

Record cognitive evaluation including fear of weight gain, perception of body shape, importance of weight in self-esteem, and insight into the condition. Document identified medical complications and results of relevant complementary tests.

Include assessment of common psychiatric comorbidities such as anxiety disorders, depression, obsessive-compulsive disorder, or personality disorders. Describe functional impact in social, occupational, and family areas.

The justification for code 6B80 should explicitly explain how the case meets diagnostic criteria, differentiating from other diagnostic possibilities considered and excluded.

6. Complete Practical Example

Clinical Case

A 17-year-old female patient, a student, presents to the mental health service referred by school medicine due to concerns about progressive weight loss. The mother reports that approximately 10 months ago the patient began a "healthy diet" following comments from classmates about her weight. Progressively, dietary restriction intensified.

On initial evaluation, the patient weighs 42 kg and is 1.62 m tall, resulting in a BMI of 16.0 kg/m² (2nd percentile for age). Ten months ago, she weighed 58 kg (BMI 22.1 kg/m², 50th percentile), characterizing a loss of 27.6% of body weight. She denies menstruation for 6 months.

On interview, she describes a highly restrictive eating pattern: consuming only fruits, vegetables, and small portions of lean protein, totaling approximately 600-800 calories daily. She completely avoids carbohydrates, dairy, and processed foods. She meticulously counts calories using an application. She exercises 90-120 minutes daily (running and abdominal exercises), even when exhausted.

She reports constant thoughts about food, weight, and body shape. She expresses intense fear of "gaining weight again," considering her previous weight "very high." When questioned about her current appearance, she states that "I still need to lose a few more kilos, especially from my belly and thighs," demonstrating significant body image distortion. She weighs herself multiple times daily, measures body circumferences, and constantly compares herself with images of models on social media.

The family reports that the patient has socially isolated herself, avoids situations involving eating, has become irritable, and presents difficulty concentrating on studies. The mother found evidence that the patient hides food and lies about having eaten.

Physical examination reveals bradycardia (48 bpm), hypotension (90/55 mmHg), hypothermia (35.8°C), dry skin, facial lanugo, and cold extremities. Laboratory tests show mild anemia, leukopenia, hypophosphatemia, and thyroid function at the lower limit of normal. Electrocardiogram demonstrates sinus bradycardia and QTc interval prolongation. Bone densitometry reveals osteopenia.

Additional psychiatric evaluation identifies moderate depressive symptoms (depressed mood, anhedonia, insomnia) and significant anxiety, particularly related to eating situations. She denies current suicidal ideation but admits occasional thoughts that "it would be better not to exist." There is no history of substance abuse, psychotic symptoms, or self-injurious behaviors.

Step-by-Step Coding

Criteria analysis:

Significantly low body weight: Confirmed. BMI of 16.0 kg/m² is well below the 5th percentile for age and significantly below 18.5 kg/m². The loss of 27.6% of body weight in 10 months is clinically severe.
Behaviors to prevent weight restoration: Present. Severe dietary restriction (600-800 cal/day), avoidance of food groups, excessive exercise, obsessive calorie counting, repeated weight checking.
Fear of weight gain: Clearly present. Verbally expresses intense fear of "gaining weight again" and desire to lose more weight despite evident malnutrition.
Body image distortion: Confirmed. Perceives herself as overweight in specific areas despite objectively low weight. Weight is central to self-evaluation.
Exclusion of organic causes: Tests performed do not demonstrate a primary medical condition explaining weight loss. The identified laboratory alterations are consequences of malnutrition.

Code chosen: 6B80 - Anorexia nervosa

Complete justification:

The case meets all diagnostic criteria for anorexia nervosa as defined by ICD-11. The BMI of 16.0 kg/m² at the 2nd percentile for age characterizes significantly low body weight. The weight loss of 27.6% in 10 months, even in isolation, would be sufficient to characterize rapid and significant loss.

The behavioral pattern is clearly directed at preventing restoration of normal weight, including severe caloric restriction, avoidance of specific foods, excessive compensatory exercise, and weight-related rituals. The fear of weight gain is explicit and disproportionate to the objective reality of low weight.

Body image distortion is evident in the discrepancy between subjective perception (need to lose more weight) and objective reality (severe malnutrition with medical complications). Weight and body shape are central to the patient's self-evaluation, significantly influencing her daily functioning.

The identified medical complications (bradycardia, hypotension, amenorrhea, osteopenia, laboratory alterations) are consistent with chronic malnutrition secondary to anorexia nervosa, not representing alternative primary conditions.

Severity is classified as severe based on the BMI of 16.0 kg/m² and the presence of multiple medical complications. The pattern is predominantly restrictive, without evidence of regular purging behaviors.

Applicable complementary codes:

Code for secondary amenorrhea (related to malnutrition)
Code for osteopenia (complication of anorexia nervosa)
Code for depressive episode if the intensity of depressive symptoms justifies additional diagnosis
Codes for cardiovascular complications (bradycardia, QTc prolongation) if clinically significant

7. Related Codes and Differentiation

Within the Same Category

6B81 - Bulimia nervosa

Use 6B81 when the patient presents with recurrent episodes of binge eating (consumption of excessive amounts of food with a sense of loss of control) followed by inappropriate compensatory behaviors (vomiting, laxatives, excessive exercise, fasting), with excessive preoccupation with weight and body shape, but maintaining weight in the normal range or above.

Main difference: Body weight is the critical differentiator. In bulimia nervosa, BMI is in the normal range (≥18.5 kg/m²) or above, whereas in anorexia nervosa (6B80) there is significant low weight. Both may present with purging behaviors, but only anorexia nervosa presents the characteristic low weight. A patient may transition between diagnoses if there is significant change in body weight.

6B82 - Binge eating disorder

Use 6B82 when there are recurrent episodes of binge eating without regular compensatory behaviors. The episodes are characterized by eating rapidly, eating until uncomfortably full, eating large amounts without physical hunger, eating alone out of shame, and feeling guilty after the episode. Typically associated with overweight or obesity.

Main difference: Absence of low body weight and absence of systematic compensatory behaviors. While 6B80 is characterized by restriction and low weight, 6B82 is characterized by episodes of binge eating without adequate compensation, often resulting in weight gain. Preoccupation with weight may be present in both, but the behavioral manifestation and weight outcome are opposite.

6B83 - Avoidant/restrictive food intake disorder

Use 6B83 when there is food restriction resulting in low weight or nutritional deficiencies, but without the specific psychopathology of anorexia nervosa. The restriction may be motivated by lack of interest in eating, avoidance based on sensory characteristics (texture, appearance, smell), or fear of aversive consequences (choking, vomiting, abdominal pain).

Main difference: The motivation for food restriction is fundamentally different. In 6B83, there is no fear of weight gain, preoccupation with body shape, or body image distortion. The restriction is not related to concerns about appearance. In 6B80, the central psychopathology involves fear of weight gain and body image distortion, with restriction being intentional for weight control.

Differential Diagnoses

Depressive disorders: May cause weight loss due to decreased appetite, but without intentional restrictive behaviors or pathological preoccupation with weight/shape. Weight loss is a consequence of anorexia (loss of appetite) associated with depression, not intentional restriction.

Anxiety disorders: May result in eating difficulties and weight loss, but without the specific psychopathology related to weight and body shape. Anxiety may affect appetite, but there are no behaviors specifically directed at weight control.

Obsessive-compulsive disorder: May present with eating rituals and preoccupations with food contamination, but without focus on weight or body shape. The distinction can be challenging when there is comorbidity, but the focus of obsessions differs.

General medical conditions: Neoplasms, gastrointestinal diseases, hyperthyroidism, type 1 diabetes, chronic infections can cause significant weight loss. Appropriate medical investigation and the absence of specific anorexia nervosa psychopathology differentiate these conditions.

Substance use: Stimulants may cause appetite suppression and weight loss, but the context of substance use and the absence of primary preoccupation with weight/body shape differentiate from 6B80.

8. Differences with ICD-10

In ICD-10, anorexia nervosa is coded as F50.0 (anorexia nervosa) with subdivisions: F50.00 (anorexia nervosa, restricting type) and F50.01 (anorexia nervosa, purging type). ICD-10 also included F50.1 for atypical anorexia nervosa, when some criteria were not fully met.

The main change in ICD-11 is the simplification of coding. Code 6B80 unifies the subtypes, eliminating the formal distinction between restricting and purging types in the coding structure. This change reflects evidence that patients frequently transition between subtypes over the course of the disorder, making the distinction less clinically useful.

ICD-11 also refines the diagnostic criteria, more clearly specifying low weight parameters (BMI <18.5 in adults, below the 5th percentile in children) and explicitly including the possibility of rapid weight loss (>20% in six months) as an alternative criterion. This inclusion recognizes that the rate of weight loss may be clinically significant even when BMI is not yet extremely low.

Another important change is the emphasis on "failure to gain weight as expected" in children and adolescents, recognizing that in this population the disorder may manifest through weight stagnation during an expected period of growth, not necessarily as absolute weight loss.

The practical impact of these changes includes greater uniformity in coding across different services and countries, facilitation of comparative epidemiological studies, and earlier recognition of the disorder in children through the criterion of failure to gain expected weight. The simplification of the code structure also reduces ambiguity in coding when patients present with mixed characteristics or transition between behavioral patterns.

9. Frequently Asked Questions

How is anorexia nervosa diagnosed?

The diagnosis is essentially clinical, based on comprehensive evaluation that includes detailed history, physical examination, and psychological assessment. There is no laboratory or imaging test that confirms the diagnosis. The professional should systematically evaluate: weight and height for BMI calculation, weight history including maximum weight and loss pattern, specific eating behaviors (restriction, purging, exercise), cognitions about weight and body shape, and functional impact. Standardized instruments such as specific questionnaires for eating disorders can assist, but do not replace clinical evaluation. Complementary tests are important for assessing medical complications and excluding organic causes of weight loss, but do not establish the diagnosis by themselves.

Is treatment available in public health systems?

The availability of specialized treatment for anorexia nervosa varies considerably among different regions and health systems. Many public health systems offer some level of treatment, although specialization and intensity may be limited. Treatment ideally involves a multidisciplinary team including psychiatrist, psychologist, nutritionist, and general practitioner. Treatment modalities include psychotherapy (especially cognitive-behavioral therapy and family therapy), nutritional rehabilitation, and medication when indicated for comorbidities. Severe cases may require hospitalization or day hospital treatment. Patients should seek information about available services in their locality through mental health centers, general hospitals, or specialized eating disorder services when they exist.

How long does treatment last?

The duration of treatment is highly variable and individualized. Mild to moderate cases may respond to outpatient treatment over 6-12 months, while severe cases often require years of follow-up. The initial phase of nutritional rehabilitation and medical stabilization may last weeks to months. Psychotherapy typically continues for a prolonged period, often 1-2 years or more. Many patients require maintenance follow-up even after significant improvement, as the risk of relapse is considerable. Factors influencing duration include initial severity, presence of medical complications, psychiatric comorbidities, family support, and treatment response. It is important to recognize that complete recovery may be gradual, and realistic expectations about timeline are essential.

Can this code be used in medical certificates?

Yes, code 6B80 can be used in official medical documentation including certificates, reports, and medical opinions. However, considerations regarding confidentiality and stigma should be weighed. In some situations, it may be appropriate to use more general terms or codes from higher categories, depending on the purpose of the document and patient preferences. For internal documentation in medical records, the specific code should always be used to ensure continuity of care and adequate record-keeping. For documents that will be accessed by third parties (employers, educational institutions), discussion with the patient about the level of diagnostic specificity is recommended, respecting principles of autonomy and confidentiality. The professional should balance the need for accurate documentation with protection of patient privacy.

Can anorexia nervosa occur in men?

Yes, although less common in men, anorexia nervosa definitely occurs in this population. Estimates suggest that approximately 10% of diagnosed cases occur in male individuals, although there may be underdiagnosis. The clinical presentation is fundamentally similar, with low weight, food restriction, fear of weight gain, and concern with body shape. Some differences may include greater focus on muscularity and body definition (vigorexia or muscle dysmorphia associated) rather than just thinness. Men may face additional barriers to diagnosis due to perceptions that eating disorders are "female conditions," resulting in delayed treatment-seeking. Code 6B80 is applicable regardless of the patient's sex.

What is the difference between anorexia nervosa and simply wanting to be healthy?

The fundamental distinction lies in the intensity, rigidity, and functional impact of behaviors, as well as the presence of specific psychopathology. Seeking healthy eating and regular exercise is adaptive behavior that improves quality of life. In anorexia nervosa, behaviors become extreme, inflexible, and harmful: severe caloric restriction resulting in malnutrition, excessive exercise despite exhaustion or injuries, intense and disproportionate fear of weight gain, significant distortion of body perception, and negative impact on social, occupational, and physical functioning. "Healthy eating" in anorexia nervosa typically involves elimination of entire food groups, rigid rituals, obsessive calorie counting, and intense anxiety related to food. Body weight falls to clinically dangerous levels, unlike maintenance of healthy weight.

Is anorexia nervosa curable?

The concept of "cure" in anorexia nervosa is complex. Many patients achieve complete and sustained recovery, returning to healthy weight, restoring normal eating patterns, and resolving psychopathology related to weight and body shape. Long-term follow-up studies indicate that approximately 50-70% of patients show complete or substantial recovery. However, the course may be chronic in some cases, with persistent or recurrent symptoms. Factors associated with better prognosis include early diagnosis and treatment, shorter disease duration before treatment, absence of purging behaviors, adequate family support, and absence of severe psychiatric comorbidities. Even after recovery, some individuals maintain vulnerability to relapse during periods of stress. Adequate and comprehensive treatment significantly increases the chances of complete recovery.

Is hospitalization necessary for all cases?

No, the majority of anorexia nervosa cases can be treated at the outpatient level with regular multidisciplinary follow-up. Hospital admission is reserved for specific high-risk situations: severe medical instability (severe bradycardia, significant hypotension, dangerous electrolyte alterations, severe dehydration), extremely low weight with life-threatening risk (typically BMI <13-14 kg/m²), imminent suicidal risk, failure of outpatient treatment with continued deterioration, or severe psychiatric complications that prevent outpatient treatment. Hospitalization focuses on medical stabilization, intensive nutritional rehabilitation, and psychological intervention in a controlled environment. After stabilization, transition to outpatient or day hospital treatment is planned. The decision about level of care should be individualized based on objective clinical criteria and the patient's and family's ability to safely adhere to outpatient treatment.

Keywords: Anorexia nervosa, ICD-11 6B80, eating disorders, low weight, food restriction, body image distortion, differential diagnosis, medical coding, multidisciplinary treatment, medical complications of anorexia.

External References

This article was prepared based on reliable scientific sources:

References verified on 2026-02-03

Anorexia Nervosa

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