Underweight

This code represents a state where an individual's body weight is below the healthy range for their age, sex, and height, often indicated by a Body Mass Index (BMI) less than 18.5 kg/m². It signifies a general lack of adequate body mass without specifying an underlying cause.

Apply this code when documentation clearly indicates a patient is underweight, typically supported by a calculated BMI below the normal threshold. This code is appropriate when the underweight status is a clinical finding or a reason for encounter, and not a symptom of a more specific condition like anorexia nervosa or malnutrition.

• Do not code this if the underweight status is explicitly documented as abnormal weight loss (R63.4), anorexia nervosa (F50.0-), or any form of malnutrition (E40-E46).
• Always review the medical record for the underlying cause of underweight; if a specific cause is identified, code that condition first, and then consider if this code is still appropriate as a secondary diagnosis.
• Ensure the documentation includes objective measures like BMI or a physician's explicit statement of "underweight."