The time required for an organ, tissue or the whole body to eliminate (excrete) one-half of an administered quantity of any substance by regular process of elimination. A biological half-life is approximately the same for both the stable and radioactive isotopes of any particular element.

Time required for an internally deposited radioactive element in a body to be diminished 50 percent as a result of the combined action of radioactive decay and biological elimination;

Effective half-life = Biological half-life X Radiological half-life

The time required for a radioactive substance to lose one-half of its activity by natural decay. Each radionuclide has a unique half-life.

Of or relating to blood.