What does LD50 measure?

• A. Lethal dose that kills 50% of animals exposed.
• B. Lethal concentration that kills 50% of animals exposed.
• C. Time to death after exposure.
• D. Dose to produce lethality in 100% of animals.

Answer: (A)

LD50 is the lethal dose that kills 50% of exposed animals, usually expressed as mg per kg of body weight. It’s determined by giving groups of animals different doses and using a statistical method to estimate the dose that results in half the animals dying. This makes LD50 a measure of dose, not concentration, and it’s specific to factors like species, strain, route of exposure, and conditions. It doesn’t describe time to death, which is a separate endpoint, and it isn’t the dose needed to kill all animals—that would be the 100% lethality dose. A related concept, LC50, refers to the lethal concentration in air or liquid, not the dose.