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The value of LD 50 for a substance is the dose required to kill half the members of a tested population after a specified test duration. LD 50 figures are frequently used as a general indicator of a substance's acute toxicity. A lower LD 50 is indicative of higher toxicity. The term LD 50 is generally attributed to John William Trevan. [2]
It is calculated using the LD50 or LC50. [1] The Occupational Safety and Health Administration (OSHA) regulation (1910.134(b)) defines the term as "an atmosphere that poses an immediate threat to life, would cause irreversible adverse health effects, or would impair an individual's ability to escape from a dangerous atmosphere."
The median lethal dose, LD 50 (abbreviation for "lethal dose, 50%"), LC 50 (lethal concentration, 50%) or LCt 50 (lethal concentration and time) of a toxin, radiation, or pathogen is the dose required to kill half the members of a tested population after a specified test duration.
Recognized effects of higher acute radiation doses are described in more detail in the article on radiation poisoning.Although the International System of Units (SI) defines the sievert (Sv) as the unit of radiation dose equivalent, chronic radiation levels and standards are still often given in units of millirems (mrem), where 1 mrem equals 1/1,000 of a rem and 1 rem equals 0.01 Sv.
It is desirous for the value of LD 50 to be as large as possible, to decrease risk of lethal effects and increase the therapeutic window. In the above formula, TI safety increases as the difference between LD 50 and ED 50 increases—hence, a higher safety-based therapeutic index indicates a larger therapeutic window, and vice versa.
The more potent a particular substance is, the steeper this curve will be. In quantitative situations, the Y-axis often is designated by percentages, which refer to the percentage of exposed individuals registering a standard response (which may be death, as in LD 50). Such a curve is referred to as a quantal dose–response curve ...
Reflect the stage of cancer; By determining the stage of cancer, it's possible to give a prognosis and treatment plan. [3] Screening for cancers; No screening test is wholly specific, and a high level of tumor marker can still be found in benign tumors. The only tumor marker currently used in screening is PSA (prostate-specific antigen ...
The 2021 U.S. Preventive Services Task Force guidelines recommend annual screening for lung cancer with low-dose computed tomography in adults aged 50 to 80 years who have a 20 pack-year smoking history and currently smoke or have quit within the past 15 years. [6]
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