If you are talking about the PQRS incentives then there are 7 different codes that can be used to report the BMI, all depending on the information in that particular visit. They are reported using the same diagnoses as the office visit (there are particular E/M codes that you can report this PQRS measure on). Some of the variables are whether the BMI is normal, above normal, below normal, documented, not documented, with or without a follow up plan, etc. The best bet is to go to
http://www.cms.gov/Medicare/Quality...ssessment-Instruments/PQRS/MeasuresCodes.html and download either the individual measures or measure groups files. This will give you the complete information you need to choose the correct codes - the BMI measure is #128 and only has to be reported once per each unique patient.
I hope this helps.