Divide the dose given by the amount in the J-code's descriptor. If the descriptor is "1 mg" and 200 mg was given, report 200 units; if it is "10 mg" and 350 mg was given, report 35. The descriptor amount, not the vial size, sets the unit.
The calculation
Units = dose given ÷ descriptor amount. The descriptor is the text of the code: "Injection, infliximab, excludes biosimilar, 10 mg" means one unit is 10 mg.
When the dose is not an exact multiple of the descriptor amount, payers differ on rounding. Follow the payer's rule and keep the documentation to show the dose actually given.
Worked examples
| Code | Descriptor amount | Dose given | Units |
|---|---|---|---|
| J9271 | 1 mg (pembrolizumab) | 200 mg | 200 |
| J1745 | 10 mg (infliximab) | 350 mg | 35 |
| J0135 | 20 mg (adalimumab) | 40 mg | 2 |
Unused drug from single-dose containers
For Medicare Part B, the amount given and the amount discarded from a single-dose container are reported separately: the discarded amount on its own line with the JW modifier, and the JZ modifier when nothing was discarded. Other payers may follow the same rule or their own.
HCPCS units vs NDC quantity
HCPCS units count descriptor amounts. The NDC quantity counts the product itself, in the unit of measure you report (ML, UN, GR, ME or F2). In the pembrolizumab example, 200 HCPCS units came from 8 mL of product: J9271 × 200, with NDC quantity ML 8.
Questions
Can units exceed a payer's limit?
Payers set per-line and per-day unit limits (Medicare's are called MUEs). A dose that legitimately exceeds one may need a modifier or documentation.