Differing definitions of obesity categories can complicate documentation.

Obesity has become one of the most serious public health problems in the United States and many other developed nations. A study published in the New England Journal of Medicine in 2017 analyzed data from 68.5 million people worldwide and estimated that over 600 million people on the planet were obese in 2015.

Image by Getty Images
Image by Getty Images

Obesity and its severity are defined and classified using body mass index (BMI). Any BMI of 30 kg/m2 or greater is classified as obesity. The CDC and World Health Organization (WHO) categorize obesity into classes 1 (30 to 34.9 kg/m2), 2 (35 to 39.9 kg/m2), and 3 (≥40 kg/m2). The NIH offers the additional classification of severe obesity, defined as a BMI corresponding to class 2 (35.0 to 39.9 kg/m2) with at least one significant obesity-related comorbidity such as type 2 diabetes, coronary disease, hypertension, or sleep apnea.

Determining the correct terminology to use in diagnosis and documentation can be confusing because of the differences among the WHO, CDC, and NIH descriptions. The CDC equivocates somewhat with respect to obesity classes by saying “Obesity is frequently subdivided into [these] categories.” Their website adds, “Class 3 obesity is sometimes categorized as ‘extreme’ or ‘severe’ obesity.” This is particularly confusing, since it's actually class 2 that is a component of the NIH's definition of severe obesity.

Further confusing the issue, ICD-10 does not recognize the three classes and includes two codes for obesity and one for overweight (Table 1). A patient who meets the NIH definition of severe obesity (that is, a BMI of 35.0 to 39.9 kg/m2 with at least one significant obesity-related comorbidity) is assigned the same code as one with a BMI of 40 kg/m2 or more.

In order for an obesity code to be assigned, a patient's BMI must be documented somewhere in the record along with a clinical diagnosis or condition, such as obesity of any severity, that makes the BMI clinically pertinent. The WHO's numbered classes of obesity should not be used alone as a clinical diagnosis or condition, since ICD-10-CM does not recognize them. “Morbid obesity” can be used to describe class 3 obesity, although this term has begun to fall out of favor. A clinician does not have to restate the BMI in her documentation.

A sound practical approach, which considers best clinical practice consistent with indications for bariatric surgery, is to define obesity as follows:

  • BMI of 40 kg/m2 or more is morbid obesity.
  • BMI of 35.0 to 39.9 kg/m2 plus at least one significant related comorbidity is severe obesity.
  • BMI of 35.0 to 39.9 kg/m2 without comorbidity is obesity.
  • BMI of 30.0 to 34.9 kg/m2 is obesity.

For the purposes of ICD-10-CM, these would be assigned the following codes: E66.01, E66.01, E66.9, and E66.9, respectively.

A BMI of 40 kg/m2 or more is classified as a comorbidity/complication (CC) that has an impact on the diagnosis-related group and severity of illness classification. Descriptive terms, such as severe obesity, are not CCs because the significance of the condition is captured more accurately by the BMI codes (Table 2) and clinicians sometimes use a descriptive term that doesn't match the BMI.

Obesity hypoventilation syndrome, also known as Pickwickian syndrome, is a condition in which poor breathing results in daytime somnolence with hypoxemia and hypercapnia in patients with a BMI greater than 30 kg/m2. This condition is assigned code E66.2, which is also a CC; this code can be used even for patients with a BMI less than 40 kg/m2.

The WHO describes obesity as a type of “malnutrition,” but controversy and confusion sometimes arise over the notion that malnutrition can be diagnosed and coded for obese patients. The conventional thinking among medical experts, insurers, and regulatory agencies in this country generally does not consider obesity to be a form of malnutrition, which is defined by inadequate caloric intake and/or excessive metabolic caloric demand.

Separately documenting and coding malnutrition as a form of obesity is not an accepted practice in the U.S. and invites scrutiny from payers and regulators. This is not to say that obese persons cannot be malnourished. Quite to the contrary, obese patients may develop conditions associated with nutritional deficiency or excess metabolic demand causing malnutrition, in which case a diagnosis of malnutrition may be established if diagnostic criteria are met.

In summary, clinicians must document a descriptive diagnostic term to express the clinical significance of a patient's BMI. Morbid obesity, defined by a BMI of 40 kg/m2 or more, and severe obesity, defined as a BMI of 35.0 to 39.9 kg/m2 with at least one related complication, are assigned the same ICD-10-CM code of E66.01. Code E66.9 is assigned for obesity, defined as a BMI of 30.0 to 34.9 kg/m2 or a BMI of 35.0 to 39.9 kg/m2 without comorbidity.

Ask Dr. Pinson

Q: Can you provide guidance on whether to include reperfusion ectopy (ventricular tachycardia or fibrillation) with or without specific treatment when a patient has undergone valve replacement or another cardiac procedure?

A: Thanks for this very interesting question. Reperfusion injury is characterized by myocardial, vascular, or electrophysiological dysfunction causing arrhythmias (typically ventricular) and is induced by the restoration of blood flow to previously ischemic tissue, as in acute myocardial infarction.

Yes, assign a code for the type of arrhythmia. I would not consider it a “complication of care” due to the procedure because it is not unexpected, but rather an intrinsic consequence of re-establishing blood flow to ischemic myocardium. Even if no specific treatment is undertaken, this condition would be closely monitored and likely prolong the length of stay, qualifying it as a secondary diagnosis.

Q: A patient was admitted for acute paroxysmal atrial fibrillation as a principal diagnosis and what was initially thought to be acute-on-chronic combined systolic and diastolic heart failure, later determined to be right-sided heart failure and left ventricular (LV) dysfunction with advanced interstitial lung disease (ILD) and severe pulmonary hypertension. An echocardiogram demonstrated a right ventricle of normal size with a right ventricular systolic pressure of 62 mmHg and moderately dilated LV with mildly to moderately reduced systolic function (ejection fraction of 40%). Would this be coded as right-heart failure due to left-heart failure (I50.814) along with systolic LV failure, unspecified acuity (I50.20) or just acute-on-chronic right-heart failure without mention of left heart failure (I50.813)?

A: Atrial fibrillation is the principal diagnosis. As for secondary diagnoses, the case description doesn't seem to make a connection between right heart failure and LV dysfunction. Right heart failure (acute, chronic, or acute-on-chronic) is assigned one of the codes from I50.81—all of which are non-complication/comorbidities (CCs).

In addition, LV “dysfunction” does not necessarily mean heart “failure.” An ejection fraction of 40% clearly indicates reduced systolic function. This documentation only supports systolic LV dysfunction (code I51.9, unspecified heart disease), which is a non-CC.

Whether LV dysfunction represents LV (heart) failure needs to be clarified and then, if heart failure is present, the acuity specified. The code assigned would depend on acuity: I50.21 (major CC) if acute, I50.22 (CC) if chronic. Because ILD was documented (code J84.9, a CC), chronic LV heart failure would not change the diagnosis-related group, but acute heart failure would by adding an MCC.