No-carrier-added (n.c.a.) and carrier-added production

'No-carrier-added' (n.c.a.) describes a radionuclide preparation in which no stable (non-radioactive) isotope of the same element has been intentionally added during manufacture or processing, though trace stable-isotope contamination can still occur incidentally, for example from reagents, the target material or the separation chemistry. 'Carrier-added' means stable isotope was deliberately added, usually to help a separation or purification step proceed. 'Carrier-free' is a stricter, largely theoretical state in which no stable isotope of the element is present at all; it is essentially never achieved or independently proven in practice for radiometals used in radiopharmaceuticals, and most style guides advise against using the term unless analytically verified.

The distinction matters most for reactor-produced radiometals. Lutetium-177 made by direct neutron irradiation of enriched 176Lu (176Lu(n,γ)177Lu) is carrier-added, because it comes out mixed with a large excess of unreacted, non-radioactive 176Lu in the same chemical form, which cannot be separated from 177Lu by ordinary chemistry since they are the same element. The alternative route, irradiating 176Yb to make 177Yb, which decays to 177Lu, gives no-carrier-added lutetium-177, because ytterbium and lutetium are different elements and can be chemically separated, leaving a batch with much higher specific activity.

These qualitative labels are convenient shorthand but are not a substitute for a measured specific or molar activity value, which is what a quality-control release specification and a clinical protocol actually need.