Body Mass Index (BMI)

Body mass index (BMI) is the topic for this monthly edition of “In the kNOW."

Body mass index is a measurement of body fat.  This calculation takes into account a person’s weight and their height.  Results are plotted on a grid, which can indicate where on a spectrum a person’s BMI rates.  High BMIs can be an indicator of high body fat, but not always.  For example, athletes may have high BMIs and yet not carry excess body fat.  For this reason, coding professionals are instructed by the Official Coding Guidelines, specifically I.B.14, to assign a BMI code only when an associated diagnosis, such as obesity, is documented by the patient’s provider.  This point is reiterated in the 4th Qtr. 2018 Coding Clinic and is further clarified by stating that the guidance applies to outpatient as well as inpatient coding.

That same issue of Coding Clinic provides additional information regarding BMI assignment.  Coding professionals are instructed to code the known BMI when an associated diagnosis is documented as long as it meets the definition of a reportable diagnosis.  While there is no list of codes for which it is acceptable to assign a BMI code, that 4th Qtr. Coding Clinic provided some clues.  Those conditions where you could expect to use a BMI code included:

•     Obesity
•     Morbid obesity
•     Overweight*
•     Underweight
•     Malnutrition
•     Anorexia nervosa (or other eating disorder)
•     Cachexia
•     Abnormal weight loss/gain
•     Failure to thrive

Coding Clinic indicated that both obesity and morbid obesity would meet the definition of reportable diagnosis as they are always considered to be of significance clinically, while the diagnosis of overweight is not.  Therefore, if there is no documentation to support clinical significance beyond a statement of overweight, do not assign either a code for overweight or BMI.  Remember that the Official Coding Guidelines Section III. Reporting Additional Diagnoses instructs inpatient-coding professionals to assign codes for other diagnoses that have an impact on patient care.  That would include any condition that requires:

•     Clinical evaluation
•     Therapeutic treatment
•     Diagnostic procedures
•     Extended length of stay
•     Increased nursing care or monitoring

Outpatient-coding professionals have a similar instruction under Section IV. Diagnostic coding and Reporting Guidelines for Outpatient Services, J. Code all documented conditions that coexist and require or affect patient care or management.   Whether assigning a code BMI on an inpatient or outpatient record, note that the BMI code is only to be assigned as a secondary code according to the guidelines.

Further direction reminds coding professionals to use the ICD-10-CM instructions when assigning the BMI for adults and utilize the age range 21 years of age or older, while for pediatric patients the age range is 2-20.

Finally, in an update to the 2018 Official Coding Guidelines, Chapter 21: Factors influencing health status and contact with health services (I.B.21.c.3) Z68 Body mass index (BMI) directs coding professionals not to assign a BMI code during pregnancy.

Now you are In the kNOW!!

About the Author 

Dianna Foley, RHIA, CHPS, CCS  is OHIMA's Coding Education Coordinator. Dianna has been an HIM professional for 20 years. She progressed through the ranks of coder, department supervisor, and department director, to her current role as a coding consultant. 

She recently served as the program director for Medical Coding and HIT at Eastern Gateway Community College. Dianna earned her bachelor's degree from the University of Cincinnati subsequently achieving her RHIA, CHPS, and CCS certifications. She is an AHIMA Approved ICD-10-CM/PCS Trainer and a a presenter at regional HIM meetings and the OHIMA Annual Meeting.