Know when it's safe to code obesity, and when you should list a code for BMI alone. The 2011 ICD-9 update added greater detail to body mass index (BMI) coding. Get the latest word on how and when to list the new codes. Get the BMI Background A person's BMI is the measure of his body fat based on his height and weight. BMI calculations are used as a tool used to estimate the range of healthy weight based on a person's height. The National Heart Lung and Blood Institute, a division of the National Institutes of Health produced the following table clinicians can use to calculate patient BMI: The NHLBI also offers the following adult BMI ranges: The 2011 ICD-9 BMI codes break down as follows: Note: As of Oct. 1, V85.4x gained a fifth digit, allowing you to be more specific with patients whose BMIs range from 40 to 70 and over. With these tools in hand, it might seem a simple next step to list an additional diagnosis code to indicate a patient's obesity or underweight, but that would be a misstep. Don't Jump to Conclusions with Obesity While you can code for BMI based on your clinical findings as a nurse, only a physician can make the determination as to whether your patient is obese, says Joan L. Usher, BS, RHIA, COS-C, ACE, with JLU Health Record Systems in Pembroke, Mass. That goes for diagnosing a patient as underweight, too. Example: You have determined that your patient has a BMI of 45.0. You have enough information to list V85.42 (Body Mass Index 45.0-49.9, adult), but you cannot list 278.01 (Morbid obesity) without further documentation from the physician. On the other hand: You will notice that instructions in your ICD-9 coding manual at 278.0x (Overweight and obesity) and 783.2x (Abnormal loss of weight and underweight) advise you to use an additional code from the V85.x subcategory to identify Body Mass Index (BMI) if known. So, if you have physician documentation of either of these diagnoses, be sure to include the appropriate BMI code as well.