Some units define the activity of a chemical, drug or biological agent:
ED = effective dose
ID = infective dose
LD = lethal dose
LC = lethal concentration
A number immediately after the abbreviation indicates the level of activity:
ED50 = 50% effective dose [dose that is effective for 50% of samples]
Such numbers used to be set as subscripts (eg LD50), but there is now a trend to set them inline. See also Pharmacokinetics and toxicokinetics.
Define these units at the first use in the text and in tables, as appropriate.
Other units are derived from terms referring to the behaviour of a biological system, or performance of an instrument. Some of these are abbreviated to lower-case initialisms, while others take capitals:
CFU = colony forming unit
PFU = plaque forming unit
cpm = counts per minute
IU = international unit
rpm = revolutions per minute
g [italic; not G] = acceleration due to gravity near Earth's surface [not ‘gravitational force’]
As with other units, do not add a plural s to these abbreviations:
Apart from very familiar ones (eg rpm), these should be defined the first time they are used in the text and in tables.
Acceleration due to gravity near Earth's surface (g) is often used as a relative unit for acceleration. An acceleration of 3 times that due to gravity can be referred to as a ‘3 g acceleration’. When specifying performance of laboratory centrifuges, g is a more useful measure than rpm because rpm does not take into account the radius of the centrifuge arm.
