What about radioactivity?
It is true that 14C is radioactive and that it must be considered when assessing which labeling to use. The level of radioactivity per test is extremely low. The body exposure from one test is significantly less than the radioactive dose given during a normal X-ray.
Furthermore in the United States a federal law was passed in1997, which allows general use of a radioactive capsule with maximum1 µCi. Statement as follows: “any person is exempt from the requirements for a license provided that such person receives, possesses, uses, transfers, owns or acquires capsules containing 37 kBq (1 µCi) carbon-14 urea, for in-vivo diagnostic use for humans.”