Q&A: BMI and morbid obesity

Q: What if a patient has a body mass index (BMI) of less than 40 but the documentation states “morbid obesity”?

A: The BMI is not a perfect calculation. BMI is a measure of body fat based on a combination of the patient's weight and height. The problem with BMI is that it can be skewed a little bit. So, for example, if we have a patient who is very muscular, their BMI is going to be higher because muscle is denser than fat.

The other time where BMI may not be accurate is during pregnancy. A pregnant patient will need to eat more calories and will weigh more during the pregnancy. So, there's going to be some limitations to BMI, but it is generally the screening tool that is used to identify risk factors in patients who are either underweight or obese.

In this scenario, the documentation isn't quite lining up with the patient’s BMI calculation. But in this case, if the provider documented morbid obesity, we're going to assign ICD-10-CM code E66.01 (Morbid [severe] obesity due to excess calories) because code assignment is dependent on the provider’s documentation.

And as I mentioned, the BMI is not a perfect calculation, so it's really going to be based on the provider’s assessment of the patient, understanding the patient's situation, and the code assignment would then be based on the provider’s documentation even though it may not quite match up to the patient’s BMI.

Editor’s note: This question was answered by Lori Amende, RHIA, CCS, a medical coding regulatory specialist for HCPro, and was originally published on JustCoding.