A J-code is a HCPCS code: J-codes are the part of HCPCS Level II, J0000 to J9999, that describes drugs, mostly ones given by injection or infusion, plus chemotherapy and some other drugs. Every J-code is a HCPCS code, but most HCPCS codes are not J-codes.
Where J-codes sit
HCPCS has two levels. Level I is CPT, for procedures and services. Level II, maintained by CMS, uses a letter followed by four digits, and the letter groups the codes: A for supplies, E for equipment, J for drugs, and so on.
J-codes cover drugs that are generally not self-administered, such as injections and infusions, and also chemotherapy drugs (J9000–J9999), immunosuppressive drugs and some inhalation solutions.
What a J-code descriptor tells you
Each J-code has a descriptor naming the drug, sometimes the route, and the amount that counts as one billing unit, for example "Injection, pembrolizumab, 1 mg". Units on the claim are the dose given divided by that amount.
Drugs without a J-code of their own
New drugs often have no specific code yet. They are billed with a not-otherwise-classified code such as J3490 (unclassified drugs) or J3590 (unclassified biologics), with the NDC and often an invoice, until CMS assigns a code. Hospital outpatient departments may use C9399 for new drugs.
Questions
How often do J-codes change?
CMS updates HCPCS Level II quarterly, so codes are added, revised and discontinued through the year. Check the current file for the date of service.