It is the onlySI prefix which uses a character not from theLatin alphabet. InUnicode, the symbol is represented byU+03BCμGREEK SMALL LETTER MU or the legacy symbolU+00B5µMICRO SIGN. The prefix "mc" is also commonly used; for example, "mcg" denotes amicrogram (whereas mg denotes amilligram).[3]
The official symbol for theSI prefixmicro is aGreek lowercase mu (μ).[6] For reasons stemming from its design,Unicode has two different character codes for the letter, with slightly different appearance in somecomputer fonts, although most fonts use the sameglyph.U+03BCμGREEK SMALL LETTER MU is in the Greek range. According toThe Unicode Consortium, the Greek letter character is preferred,[7] but implementations must recognize the micro sign as well, forcompatibility with legacy character sets. This distinction also occurs in some legacy code pages, notablyWindows-1253.
In circumstances in which only theLatin alphabet is available,ISO 2955 (since 1974,[8] withdrawn 2001[9]),DIN 66030 (since 1980[10][11]) andBS 6430 (since 1983) allow the prefixμ to be substituted by the letter⟨u⟩ (U+0075uLATIN SMALL LETTER U) as, for example, inum forμm, oruF forμF.Similarly, capacitor values according to theRKM code defined inIEC 60062 (since 1952) can be written as4u7 (or4U7) instead of4μ7 if the Greek letterμ is not available.
TheCJK Compatibility block contains square forms of some Japanesekatakana measure and currency units.U+3343㍃SQUARE MAIKURO corresponds toマイクロmaikuro.
In somehealth care institutions, house rules deprecate the standard symbol formicrogram, "μg", in prescribing or chart recording, because of the risk of giving an incorrect dose because of the misreading of poor handwriting.[12] The two alternatives are to abbreviate as "mcg"[12][3] or to write out "microgram" in full (see alsoList of abbreviations used in medical prescriptions). The alternative abbreviation may be ambiguous in rare circumstances in thatmcg could also be read as amicrigram, i.e. 10−14 g; however the prefixmicri is not standard, nor widely known, and is considered obsolete. This deprecation, focused on avoiding incorrect dosing in contexts where handwriting is often present, does not extend to all health-care contexts and institutions (for example, some clinical laboratories' reports adhere to it, whereas others do not[12]), and inphysical sciences research, "μg" remains the sole official abbreviation.
In medical data exchange according to theHealth Level 7 (HL7) standard, the μ can be replaced by u as well.[13]
