The LD may be based on the standard person concept, a theoretical individual that has perfectly "normal" characteristics, and thus not apply to all sub-populations.
The choice of 50% lethality as a benchmark avoids the potential for ambiguity of making measurements in the extremes and reduces the amount of testing required.
One form of measuring LD is to use model organisms, particularly animals like mice or rats, converting to dosage per kilogram of biomass, and extrapolating to human norms.
The U.S. Food and Drug Administration has begun to approve more non-animal methods in response to animal welfare concerns.
[5] The median infective dose (ID50) is the number of organisms received by a person or test animal qualified by the route of administration (e.g., 1,200 org/man per oral).
The lowest lethal dose (LDLo) is the least amount of drug that can produce death in a given animal species under controlled conditions.
[6][7] The dosage is given per unit of bodyweight (typically stated in milligrams per kilogram) of a substance known to have resulted in fatality in a particular species.
For gases and aerosols, lethal concentration (given in mg/m3 or ppm, parts per million) is the analogous concept, although this also depends on the duration of exposure, which has to be included in the definition.
These measures are commonly used to indicate the comparative efficacy of chemical warfare agents, and dosages are typically qualified by rates of breathing (e.g., resting = 10 L/min) for inhalation, or degree of clothing for skin penetration.
[citation needed] Some chemicals, such as hydrogen cyanide, are rapidly detoxified by the human body, and do not follow Haber's Law.
[citation needed] The LCLo is the lowest concentration of a chemical, given over a period of time, that results in the fatality of an individual animal.