An NDC identifies a specific drug product and package as listed with the FDA. A J-code is a HCPCS billing code that describes a drug and a dosage amount regardless of who made it or how it is packaged. One J-code usually covers many NDCs, and many NDCs have no J-code.
What each code identifies
The NDC answers "which product, from which labeler, in which package". The J-code answers "which drug, and how much of it counts as one unit". Two vials of the same drug from different labelers have different NDCs and the same J-code.
Who assigns them
The labeler assigns the product and package segments of an NDC and lists them with the FDA. CMS assigns HCPCS Level II codes, including J-codes, and updates them quarterly.
How quantity is counted
HCPCS units come from the code descriptor: the dose divided by the descriptor amount. NDC quantity is reported separately, with a unit qualifier (F2, GR, ME, ML or UN) and the amount of the NDC product used. The two numbers are usually different and both have to be right.
How both appear on a claim
On a professional claim the HCPCS code and units go in the service line, and the NDC goes in the supplemental information for the same line as N4 followed by the 11-digit NDC, the unit qualifier and the quantity. Institutional claims carry the same NDC information on the line with the revenue code and HCPCS code.
Questions
Can I find the J-code from an NDC?
Only through a crosswalk. Med-Code shows a J-code on an NDC page when its curated directory has an exact match for that product; otherwise it says that no code was found rather than guessing.