# DIN EN 12435-2006

!1“3389 +##+ +#: + 7“2!1;“33 (is more than), (is less than or equal to), (is more than or equal to), § (is approximately equal to) or (is not equal to) (ISO 31-11: 1992, Clause 3). NOTE ENV 1614 “Medical informatics Messages for the exchange of laboratory information“ concentrates on the elements of information on the left of the relational operator. This ENV complements that work and concentrates on the right of the relational operator. 5 Units for reporting information in health sciences 5.1 Representation of results of measurements In the representation of results of measurements, the unitary expressions shall include any of the following: SI units (Clauses 5.1 to 5.3) units formed from SI units by use of prefix symbols (Clause 5.4) certain off-system units (Clause 5.5) certain dimensionless units (Clause 5.6). 5.1.1 Annex A provides conversion factors with which algorithms can be designed to convert other units in local use and Annex C provides some criteria for conversion between kinds-of-quantity. 5.1.2 Table 1 lists SI base units each with its associated base kind-of-quantity. Definitions of the SI base units are given in Annex A. Number of entities is sometimes also treated as base and has the coherent SI unit `one . For the choice of kilogram (with a prefix) as a base unit see Clause 5.4.6. EN 12435:2006 (E) 12 Table 1 Base kinds-of-quantity, base units and their dimensional symbols in the International System of Units (SI). The base kinds-of-quantity are in the sequence used by CGPM and in Annex A. Entries begin with the references (Ref.) to that annex. Base kind-of-quantity Base unit Ref. name symbol name symbol Dimension A.1 number (of entities) N one 1 1 A.2 length l metre m L A.10 mass m kilogram kg M A.19 time t second s T A.66 electrical current I ampere A I A.87 thermodynamic temperature T, ϑ kelvin K , A.102 luminous intensity Iv candela cd J A.107 amount-of-substance n mole mol N 5.2 Derived coherent units of SI and mathematical operations with units 5.2.1 Most coherent units of derived kinds-of-quantity are represented with compound units obtained by multiplication or division or both of the component base units. Such expressions require the mathematical operations of multiplication, division and raising to a power. EXAMPLE Mole per square metre second (mol m-2 s-1) is the SI-coherent compound unit of areic substance rate (Annex A.120). 5.2.2 Multiplication between units shall be represented by either a space, by a half-raised point ( · ) or by raising to a power. EXAMPLES The product of pascal and second (called pascal second) is represented as Pa s or Pa · s. The product of 2 Pa s with 5 s-1 is 2 Pa s X 5 s-1 = (2 Pa s) · (5 s-1) = 10 Pa. NOTE 1 The multiplication sign X is not recommended by ISO 31-0 for expression of units. NOTE 2 The space between a numerical value and a unit also represents multiplication. NOTE 3 Raising a unit u to a power is usually expressed as `unit squared (u2), `unit cubed (u3) or `unit to the fourth power (u4). For units of length, the designations `square unit and `cubic unit (e.g. square metre and cubic metre) are used as long as the derived quantity can be viewed as an area and a volume, respectively. Otherwise EN 12435:2006 (E) 13 designations like metre squared and metre cubed are used. In Annex A, only designations like square metre and cubic metre are listed. 5.2.3 Division of units shall be represented by multiplication of negative powers (example above) or by a slash (/). Not more than one slash shall be used in one compound unit, unless brackets are used in the expression to avoid ambiguity. EXAMPLE mol m-2 s-1 = mol·m-2·s-1 = mol/(m2 s) = (mol/m2)/s but not mol/m2/s 5.3 Derived coherent units of SI with special names and symbols Special names or symbols, usually both, are allowed for certain derived SI units (Table 2). 5.4 Multiples and submultiples of units: prefix names and symbols 5.4.1 If a system of units is chosen with only one unit for each dimension, there are bound to be some very large and very small numerical values, which can be expressed more briefly by use of powers of 10, such that numerical values (i.e. the mantissas) can almost always be between 0,1 and 1000 (Subclause 6.1.3). EXAMPLES Molar number constant, NA, ≈ 602 213 670 000 000 000 000 000 mol-1 = 602,213 67·1021 mol-1 Rest mass of an electron, me ≈ 0,000 000 000 000 000 000 000 000 000 000 9 kg = 0,9·10-30 kg 5.4.2 Instead of using powers of 10 with numerical values, decimal prefixes may be attached to SI units. The prefixes Table 2 Kinds-of-quantity associated with derived SI units with special names or symbols. The sequence of the list is as in Annex A, to which the references (Ref.) apply, essentially by order of dimension (Table 1) with increasing magnitude of powers of those dimensions, first positive and then negative. The trivial names of some kinds-of-quantity (A.44, equivalent dose) imply also an unnamed generalized component (marked by the modulus sign, |, in the systematic name). Systematic names of electrical and luminous kinds-of-quantity are based on electrical charge (unit C = A s) and quantity of light (unit lm s = cd sr s), respectively. The distinction electric and electrical is a non-normative mental aid in marking those kinds-of-quantity in which electrical charge forms part of the denominator and numerator, respectively, of the definition. The name and symbol of the katal have been recognized by IUPAC, IFCC, IUBMB and WHO; other units are recognized also by BIPM (1991). The symbols t, ϑ and Φ have several meanings in Table 1 and 2, those of Þ being distinguished here by subscripts. Kind-of-quantity Ref. name symbol name Unit symbol Definition in SI-base units A.1 plane angle γ, ϑ α, β, radian rad m m-1 = 1 A.1 solid angle Ω steradian sr m2 m-2 = 1 EN 12435:2006 (E) 14 A.20 number rate | of regular events; frequency f, ν hertz Hz s-1 A.20 radioactivity A becquerel Bq s-1 A.44 massic energy | of ionizing radiation absorbed; absorbed dose D gray Gy m2 s-2 A.44 effective massic energy | of ionizing radiation absorbed; equivalent dose H sievert Sv m2 s-2 A.48 force F newton N kg m s-2 A.50 pressure p pascal Pa kg m-1 s-2 A.51 energy E, Qe joule J kg m2 s-2 A.58 energy rate; power P, Φe watt W kg m2 s-3 A.61 electrical charge Q coulomb C A s A.72 magnetic induction; B tesla T kg A-1 s-2 magnetic flux density = kg C-1 s-1 A.74 magnetic flux Φm weber Wb kg m2 A-1 s-2 = kg m2 C-1 s-1 A.76 electric potential U, V volt V kg m2 A-1 s-3 difference = kg m2 C-1 s-2 A.78 mutual inductance L henry H kg m2 A-2 s-2 = kg m2 C-2 A.80 electrical conductance G siemens S A2 s3 kg-1 m-2 = s C2 kg-1 m-2 A.81 electric resistance R ohm Ω kg m2 A-2 s-3 = kg m2 C-2 s-1 A.85 electrical C farad F A2 s4 kg-1 m-2 EN 12435:2006 (E) 15 capacitance = C2 s2 kg-1 m-2 A.87 Celsius temperature t, ϑ degree °C K A.102 light rate; luminous flux Φv lumen lm cd sr A.103 areic light rate | of incident radiation; illuminance Mv lux lx cd sr m-2 A.119 catalytic activity z katal kat mol s-1 Table 3. SI prefixes denoting decimal factors, 10n. m = 3n. The origins of the prefixes are indicated as an aid for memorization: Da, Danish; Es, Spanish; Gr, Greek; It, Italian; La, Latin; No Norwegian. Name Symbol n m Mnemonic yotta Y 24 8 La octo (8) zetta Z 21 7 La septem (7) exa E 18 6 Gr hexa (6) peta P 15 5 Gr penta (5) tera T 12 4 Gr (monster) giga G 9 3 Gr gigas (giant) mega M 6 2 Gr megas (great) kilo k 3 1 Gr chilioi (1000) hecto h 2 Gr hekaton (100) deca da 1 Gr deka (10) deci d -1 La decem (10) centi c -2 La centum (100) milli m -3 -1 La mille (1000) EN 12435:2006 (E) 16 micro µ -6 -2 Gr mikros (small) nano n -9 -3 La nanus (dwarf) pico p -12 -4 Es pico, It piccolo (small) femto f -15 -5 Da, No femten (15) atto a -18 -6 Da, No atten (18) zepto z -21 -7 La septem (7) yocto y -24 -8 La octo (8) shall be in accordance with Table 3, forming a series from 10-24 to 1024. Since the distinction between capital letters and lower-case letters is significant for the meaning of the prefix symbols, capitals shall be used consistently for the higher positive powers from mega (106) upwards. 5.4.3 In data formatted for interchange, the decimal factors and decimal prefixes should give steps of a factor 1000 (i.e. a power of 103n, where n is a positive or negative integer). NOTE For convenience in health sciences, the prefixes hecto, deca, deci and centi can usually be avoided (Table 3, separated by dotted lines), though they have equal legal standing. 5.4.4 A unit together with a prefix forms a new unit, which shall be displayed or printed according to the rules for units. The new unit as a whole can be multiplied, divided or raised to a power. EXAMPLE A kilometre (km) is 1000 m and square kilometre (km2) is (1000 m)2, i.e. 1 000 000 m2, not 1000 m2. 5.4.5 A second prefix shall be avoided in units already containing a prefix, either in simple units (e.g. not µµg but pg) or compound units. EXAMPLE The substance concentration of a pollutant in air shall be expressed as 8 µmol m-3 and not as nmol dm-3 (but may alternatively be expressed as 8 nmol/L, Subclause 5.5.2). 5.4.6 Since the base unit kilogram (kg) already contains a prefix, multiples shall be constructed by adding prefixes to the submultiple unit gram (g). EXAMPLES The multiple 103 kg shall be expressed as megagram (Mg) equal to 103 kg (not 106 kg). It is not called kilokilogram (kkg). Multiples of the unit kilogram metre (kg m) shall be made by replacing the `k- of kg and not by inserting an additional prefix to metre: mg m, not kg µm. 5.4.7 A prefix shall be attached to a numerator unit rather than to a denominator unit or to a unit raised to a power, because of difficulties of interpretation. EXAMPLE 100 m-1 = (10-2 m)-1 = cm-1 (though recognized for wavenumber, Annex A.3) 0,01 m-1 ≠ cm-1 EN 12435:2006 (E) 17 5.4.8 If a compound unit has to be simplified, it should first be converted to numerical factors and coherent units. EXAMPLE 10-18 mol m-2 s-1 = amol m-2 s-1 (preferred) = mol (109 m)-2 s-1 = mol Gm-2 s-1 (avoid) = mol m-2 (1018 s)-1 = mol m-2 Es-1 (avoid) 5.4.9 Quantities with mass in the denominator of the definition should be expressed in compound units with kg-1 rather than g-1. EXAMPLE Molality is expressed in mol kg-1 or mmol kg-1, rather than mmol g-1 or µmol g-1. 5.4.10 The order of unit-symbols in compound units is not strictly determined in normal usage. Criteria should include the following: positive powers precede negative powers the unit of mass (e.g. kg, g, mg) precedes other units in the numerator and in the denominator. if avoidable, a letter that might be misunderstood as a prefix symbol should not be initial. EXAMPLE N m (newton metre) rather than m N (metre newton), which may be confused with mN (millinewton) 5.5 Units outside SI: off-system units 5.5.1 For certain kinds-of-quantity, results may be expressed in either SI units and their multiples, or units outside SI. If units outside SI are used, they shall be in accordance with Table 4, in accordance with recognition by CGPM, the EU Directive, IUPAC, IFCC, IUBMB and WHO (or WHA). In medical informatics, those with asterisks (Table 4) are discouraged. Table 4 Units outside SI recognized for use together with SI in health sciences. For experimentally obtained values, with combined standard uncertainty uc (explained in Annex D). Units marked with an asterisk (*) are not normally required for health sciences, though they have general, specialized or temporary legal recognition (EU* meaning temporary or limited recognition by the European directive); month and year have various definitions, those given here being the month of 30,4 days and the tropical year. References (Ref.) are to Annex A. Unit Ref. name symbol Value in SI unit or multiple Authority A.1 degree (of arc) ° = (pi/180) rad CGPM, EU A.1 *minute (of arc) ′ = (pi/10 800) rad CGPM, EU EN 12435:2006 (E) 18 A.1 *second (of arc) ″ = (pi/648 000) rad CGPM, EU A.3 *dioptre dpt, d = m-1 EU* A.4 *hectare ha = 10 000 m2 CGPM, EU A.4 *are a = 100 m2 CGPM, EU* A.6 litre L, l = 0,001 m3 = dm3 CGPM, EU A.10 *tonne; t = 1000 kg CGPM, EU *metric ton A.10 dalton; Da ≈1,660 540 2 yg; IUBMB *atomic mass unit u uc = 0,000 001 0 yg CGPM, EU A.19 year - ≈ 31,556 9 Ms A.19 *month - ≈ 2,626 56 Ms A.19 week - = 604 800 s A.19 day d = 86 400 s CGPM, EU A.19 hour h = 3600 s CGPM, EU A.19 minute min = 60 s CGPM, EU A.50 *bar bar = 100 kPa EU A.50 millimetre-mercury mmHg = 133,322 Pa EU*, WHA A.51 electronvolt eV ≈ 160,217 733 zJ; CGPM, EU uc = 0,000 049 zJ A.135 international unit int.unit, iu variable WHO, IUPAC, IFCC A.135 arbitrary unit arb.unit variable IUPAC, IFCC 5.5.2 A stumbling block for acceptance of SI in health sciences is the coherent unit of volume, the cubic metre. The litre (Table 4, A.6) is the preferred unit of volume in expressing concentrations. NOTE 1 A switch to the cubic metre requires only a switch by a factor 10-3. The preferred way of expressing concentration is usually as substance concentration in moles per litre and its multiples (mol L-1, mmol L-1, ) rather than in kilomoles per cubic metre and its multiples (kmol m-3, mol m-3, ) (Annex A.113.2). EN 12435:2006 (E) 19 NOTE 2 The symbols L and l have equal legal status. The capital L has been used in this document. The letter l is inadvisable if the letter type does not allow distinction from the numeral 1. 5.5.3 The name dalton and symbol Da (Table 4, A.10) are used in biochemistry, molecular biology and clinical sciences instead of unified atomic mass unit (u); the size of macromolecules, cell components and virus particles should preferably be expressed as molar mass (Annex A.117.2). 5.5.4 Minute and hour, and sometimes day, week, month and year are often needed for expression of calendar time, clock time and time intervals. For derivatives of time, the second is preferred, though other units are hard to avoid. In the compound units of rates (i.e. time derivatives), use of minute, hour and day should be avoided to simplify comparison of data. If such stringency is not possible, the same unit of time (e.g. day) should at least be used throughout a set of data. EXAMPLE For substance rate (Annex A.119.1), preferably mol s-1, mmol s-1, mol s-1, but alternatively kmol d-1, mol d-1, mmol d-1 . 5.6 Units of dimensionless quantities and compound units with the unit `one in the numerator 5.6.1 If the exponents of the dimensional term (Annex B) are all zero, the quantity is said to be of dimension one or dimensionless: L0M0T0I0θ0J0N0 = 1 EXAMPLES - number of entities of component (Subclause 5.1, Table 1; Annex A.1.1), - dim NB = 1 - substance fraction (Annex A.1.1), dim xB = 1 - relative quantities such as relative volumic mass (Annex A.1.1), dim ρr = 1 5.6.2 For quantities of dimension one, the coherent uni