Body mass index is a heavy topic.

Spring has arrived in the Northeast and people are getting back to their exercise schedules. I was thinking about this topic as I was reading Coding Clinic, Fourth Quarter 2018. One of the big topics in this issue is body mass index (BMI) (Z68.-).

The Official Coding Guidelines state that the BMI may be documented by other clinicians, but the associated diagnosis (such as obesity) must be documented by the patient’s provider. This issue is also supported by the Coding Clinic which goes on to state that “overweight” must meet the conditions for reporting a secondary diagnosis. Those conditions are the following:

  1. Clinical evaluation; or
  2. Therapeutic treatment; or
  3. Diagnostic procedures; or
  4. Extended the length of hospital stay; or
  5. Increased nursing care and/or monitoring.

This issue of Coding Clinic supports that the BMI can only be reported whenever a weight diagnosis is documented by the provider.  Failure to thrive (adult – R62.7; child over 28 days old – R62.51) and underweight (R63.6) are considered weight diagnoses so the BMI is appropriate to report. For those who are reporting Hierarchical Condition Categories (HCCs), remember that morbid obesity (E66.01) is an HCC and would be supported by the BMI.   Morbid obesity and obesity (E66.9) are always reportable when documented by the provider.

The ICD-10-CM BMI code for patients at age 20 is based on the classification direction which is pediatric.  This guidance was given knowing that the Center for Disease Control (CDC) growth charts for patients 20 years old are listed as adult. The coder is required to follow the classification based on the Official Coding and Reporting Guidelines.

Many electronic medical records (EMRs) list the BMI automatically. These codes are not intended for routine capture.    

It is not appropriate to assign the diagnosis code based on BMI. This topic was discussed in the Official Coding Guidelines, Section I.A.19, “Code assignment is not based on clinical criteria used by the provider to establish the diagnosis.” (The topic was also discussed in Coding Clinic, Fourth Quarter 2016, pg. 147-149.)  Code assignment is based on the physician’s documentation for the weight diagnosis.

Some new insight in this issue was to not code the BMI for OB patients. This information is reflected in the update of the Official Coding and Reporting Guidelines.   It is appropriate to report “obesity complicating pregnancy (O99.21-),” if documented by the provider. 

It is important to report these codes accurately as the BMI less than 20 or greater than 40 is considered a complication/comorbid condition (CC) in the Medicare Severity Diagnosis Related Group (MS-DRG) methodology. These codes are also part of the HCC methodology as well as the Shared Services Program (SSP). Because of their “weight” throughout healthcare reimbursement methodologies, they can be targeted for regulatory review.   

The U.S. Department of Health and Human Services (HHS) Office of Inspector General (OIG) has done reviews on the topic of malnutrition with millions of dollars returned to Medicare. So be careful, where you code weight and ensure that the clinical documentation and coding guidance supports the condition and associated BMI.


2019 Official Coding and Reporting Guidelines 
Coding Clinic, Fourth Quarter 2018


Laurie M. Johnson, MS, RHIA, FAHIMA, AHIMA Approved ICD-10-CM/PCS Trainer

Laurie Johnson is currently a senior healthcare consultant for Revenue Cycle Solutions, based in Pittsburgh, Pa. Laurie is an AHIMA-approved ICD-10-CM/PCS trainer. She has more than 35 years of experience in health information management and specializes in coding and related functions. She has been a featured speaker in over 40 conferences. Laurie is a member of the ICD10monitor editorial board and is a permanent panelist on Talk Ten Tuesdays

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