Abstract
The terminology of NPU (nomenclature for properties and units) aims at describing properties examined in clinical laboratories for a patient. It was originally jointly approved in 1966 by IUPAC and by the International Federation of Clinical Chemistry (IFCC) and covers multiple disciplines in the field of clinical laboratory sciences, including clinical allergology, clinical chemistry, clinical haematology, clinical immunology and blood banking, clinical microbiology, clinical pharmacology, molecular biology and genetics, reproduction and fertility, thrombosis and haemostasis, and toxicology. The NPU terminology adheres to international standards of metrology and of terminology, in particular the International System of Quantities (ISQ) and International System of Units (SI), the International Vocabulary of Metrology (VIM), and also to ‘An outline for a vocabulary of nominal properties and examinations – basic and general concepts and associated terms,’ recently prepared on behalf of the IFCC-IUPAC Committee-Subcommittee on Nomenclature for Properties and Units. The present document recalls the definitions of the concepts used to express a property of a patient, regarded as a system. The aim is to promote by this comprehensive summary the proper NPU terminology for reliable exchange of patient examination data. The use of this syntax and of SI units enables the translation of these descriptions into other languages without loss of meaning or accuracy. The NPU format is also well adapted for comparative and epidemiological studies. More information will be found in the upcoming 2nd edition of the Compendium of Terminology and Nomenclature of Properties in Clinical Laboratory Sciences, the IUPAC and IFCC ‘Silver Book’, and in the recently published ‘Properties and units in the clinical laboratory sciences. Part XXIII. The NPU terminology, principles, and implementation: A user’s guide (IUPAC Technical Report)’ (DOI:10.1351/PAC-REP-11-05-03).
1 Definitions of basic concepts used in the NPU format
The terminography used in the examples below adheres to the NPU format where each of the three main elements of a property term may be augmented by a parenthetic specification, following without preceding space:
System(specification)–Component(specification); kind-of-property(specification)
= nominal property value or quantity value and unit as appropriate.
system: part or phenomenon of the perceivable or conceivable world consisting of a demarcated arrangement of a set of components and a set of relations or processes between these components (modified from ref. [1])
In human biology, it may be the patient or a body part of the patient or the immediate surroundings, e.g. person, blood, urine, kidney, beta cells of the pancreas, Exhaled air. In the NPU format, the initial letter of the term for a system is a capital letter.
component: part of a system [1]
The component may be a physical part of the system, a chemical or biochemical compound, or a process; e.g., calculus, glucose, intestinal absorption, cortisol secretion. In the NPU format, the initial letter of the term for a component is a capital letter.
kind-of-property: aspect common to mutually comparable properties [modified ref. 1, 2]
The term of this concept is hyphenated to emphasize that it is a single term.
Examples are number concentration (C), volume (V), amount-of-substance (n), substance concentration (c), catalytic-activity concentration (b), taxon, sequence variation.
dedicated kind-of-property: kind-of-property with given sort of system and any pertinent sorts of component [1]
Patient–Glucose; substance concentration(procedure)
Patient–; mass
In the last example, no component is relevant.
property: inherent state- or process-descriptive feature of a system including any pertinent components [1]
Patient(Urine)–Glucose; substance rate(procedure) = 8 mmol/day.
The term “procedure” refers to the examination procedure. As the scale will depend on the local procedure, this procedure should be indicated in the report.
First efforts at the standardization of data transmission in clinical laboratories concerned quantities, i.e. those properties that have a magnitude, mostly expressed by a number and a unit [3]. However, many important properties of a classificatory nature such as species of microbes or genetic structure are inherently devoid of magnitude [4]. In such a case, the superordinate concept ‘property’ can be generically divided into five types of property according to algebraic characteristics [1]:
nominal property: property defined by an examination procedure, that can be compared for identity with another property of the same kind-of-property, but has no magnitude [modified ref.1].
Urine–Neuroleptic drug; taxon(procedure) = chlorpromazine.
ordinal property, ordinal quantity: property, defined by an examination procedure, having a magnitude and that can be stated only to be lesser than, equal to, or greater than another property of the same kind-of-property [1]
Urine–Bilirubins; arbitrary concentration(procedure) = 2.
The plural “bilirubins” indicates the sum of the neutral and ionic forms of bilirubin.
differential property, differential quantity: property having a magnitude and that can be subtracted from, but cannot be divided by, another property of the same kind-of-property [1]
Patient–Rectum; Celsius temperature = 36.5 °C.
logarithmic differential property is used when the measurement scale consists of logarithmic values
Urine–; pH = 6.1.
rational property, rational quantity: property having a magnitude and that can be divided by another property of the same kind-of-property [1]
Blood–Erythrocytes; volume fraction = 0.41 = 41 %.
quantity: property of a phenomenon, body, or substance, where the property has a magnitude that can be expressed by a number and a reference [5]
A reference may be a measurement unit, a measurement procedure, a reference material, or a combination of such.
kind-of-quantity: aspect common to mutually comparable quantities ([5] but without hyphens in the term)
Each kind-of-quantity may be designated by a term or a symbol, e.g., length (l), and mass concentration (ρ). A given kind-of-quantity may have synonyms; e.g., relative molecular mass and molecular weight (deprecated by the ISO), and also synonymous symbols; e.g., A and S for area. A given symbol is sometimes used for different kinds-of-quantity; e.g., A is the recognized symbol for area, nucleon number, Helmholtz free energy, affinity of chemical reaction, and absorbance. The concepts here termed “kinds-of-quantity” are generally termed “quantity” by CGPM [6], BIPM [5], and ISO/IEC 80000-1 [7].
quantity of dimension one, also termed “dimensionless quantity”: quantity for which all the exponents of the factors corresponding to the base quantities in its quantity dimension are zero [5]:
Quantities of dimension one may be divided according to their kind-of-quantity into fractions, ratios, and relative kinds-of-quantity:
fraction: quotient of two identical kinds-of-quantity, for which the numerator kind-of-quantity relates to a component B and the denominator kind-of-quantity relates to the given system
Erythrocytes(Blood)–Reticulocytes; number fraction = 6 × 10–3 = 0.6 % = 6 ‰.
ISO/IEC 80000-1 accepts per cent (percent in the Green Book) with the symbol % for the submultiple unit 0.01, and per mille (permille in the Green Book) with the symbol ‰ for the submultiple unit 0.001.
ratio: quotient of two identical kinds-of-quantity, for which the numerator kind-of-quantity relates to a component B and the denominator kind-of-quantity to another component of the same system, commonly treated as a reference component
Sweat(specification)–Sodium ion/Potassium ion; substance ratio = 3.80 = 380 %.
relative kind-of-quantity: quotient of two identical kinds-of-quantity, commonly two kinds-of-quantity related to different systems, the second being a reference system
Plasma–Coagulation factor XI; relative substance concentration(immunological; actual/norm; procedure) = 0.80 = 80 %.
arbitrary kind-of-quantity: kind-of-quantity outside the ISQ
There is no dimension or SI unit involved.
Thrombocytes(Blood)–Aggregation, collagen-induced; arbitrary activity(normal; lightly weakened; weakened; utmost weakened; procedure) = lightly weakened.
This example is also an ordinal quantity.
2 Generalities concerning kinds-of-quantity and units
‘Kinds-of-quantity’ are used to classify quantities of the same kind. Quantities of the same kind within a given system of quantities have the same dimension. Different kinds-of-quantity can also have the same dimension:
Substance content (nB/msystem) and molality (nB/msolvent) both have the dimension N M–1 and the coherent SI unit mol kg–1.
2.1 Base kinds-of-quantity in the ISQ, their dimensions, and their units in the SI
A base kind-of-quantity is one that is conventionally accepted as being independent of other base kinds-of-quantity in a system of kinds-of-quantity. The remaining kinds-of-quantity are derived and are related to base or derived units. To each base kind-of-quantity of the ISQ is assigned a dimension represented by a sans-serif capital-letter symbol (except for number of entities) (Table 1). For example, the dimension of amount-of-substance is represented by N. Number of entities can be regarded as a base kind-of-quantity [5, § 1.4 note 3; 9, part 1, § 3.4 note 3] and the number one (symbol 1) as a base unit [5, § 1.10 note 3].
Base kinds-of-quantity, base units, and their dimensional symbols of the International System of Units (SI).
| Base kind-of-quantity | Base unit | Dimension | ||
|---|---|---|---|---|
| Term | Symbol | Term | Symbol | Symbol |
| Number (of entities) | N | One | 1 | 1 |
| Length | l | Metre | m | L |
| Mass | m | Kilogram | kg | M |
| Time | t | Second | s | T |
| Electrical current | I | Ampere | A | I |
| Thermodynamic temperature | T | Kelvin | K | Θ |
| Amount-of-substance | n | Mole | mol | N |
| Luminous intensity | Iv | Candela | cd | J |
Amount-of-substance should not be termed “number of moles.” The amount-of-substance does not equal number of entities, but is proportional to number of specified entities that may be atoms, molecules, ions, electrons, other particles, or groups of such particles [6].
Urine–Nitrogen(N); amount-of-substance(procedure) = 360 mmol.
The relationship is governed by the Avogadro constant (symbol NA or L):
The abbreviation of “amount-of-substance” in derived kind-of-quantity terms is “am.s.” in the IUPAC and IFCC Silver Book [8] and in the NPU format, but “amount” in the IUPAC Green Book [9].
2.2 Symbols of derived kinds-of-quantity, coherent derived SI units, and quantity dimensions
Striving for monosemy, i.e. one symbol only relates to one concept, single letters are sometimes modified by subscripts, superscripts, or different fonts, e.g., Ar is the symbol for relative atomic mass (atomic weight), and Am is that for molar radioactivity. N is the dimensional symbol of amount-of-substance, and N is the symbol of the unit newton.
The unit degree Celsius is symbolized °C, and a Celsius temperature is given, e.g., as 37 °C (not 37, 37° C, 37°C, or 37C).
The term “katal” and symbol “kat” for the ‘coherent derived unit of catalytic activity’ have been recognized by IUPAC, IFCC, International Union of Biochemistry and Molecular Biology (IUBMB), World Health Organization (WHO), and General Conference on Weights and Measures (CGPM) [6]. IUPAC and IFCC [10] recommended that the enzyme unit, international unit U, be progressively replaced by submultiples of the katal where
1 U = 1 μmol/min ≈ 16.67 nkat
Plasma–Aspartate transaminase; catalytic-activity concentration(IFCC 2002) =
2.2 × 10–6 kat/L = 2.2 μkat/L.
A specification regarding the measurement procedure used is necessary when catalytic activity is involved, here ‘IFCC 2002’. If the symbol U is used, it must not be confused with the symbol IU (meaning International Unit, also abbreviated int.unit), which is the symbol used by the WHO and mentioned in the SI Brochure [6] in expressing biological activity of certain substances that cannot yet be defined in terms of the SI:
Plasma–Insulin; arbitrary substance concentration(IRP 66/304; procedure) = 120 × 10–3 IU/L,
where IRP stands for international reference preparation of the WHO.
2.3 Non-SI units
Several non-SI units are widely used in clinical laboratory sciences and have corresponding values in SI units (Table 2).
Some derived units of the International System of Units (SI) with special terms or symbols.
| Kind-of-quantity | Term for unit | Symbol for unit | Expression in terms of SI coherent unit |
|---|---|---|---|
| Length | Ångström | Å | = 0.1 × 10–9 m |
| Volume | Litre* | L, l | = 10–3 m3 |
| Mass | Dalton* | Da | = 1.660 538 921(73) × 10–27 kg |
| Time | Minute* | min | = 60 s |
| Hour* | h | = 3600 s | |
| Day* | d | = 86.4 × 103 s | |
| Week | wk | = 604.8 × 103 s | |
| Year (tropical) | a | ≈ 31.556 952 × 106 s | |
| Pressure | Millimetre of water | mmH2O | = 9.806 65 Pa |
| Millimetre of mercury | mmHg | ≈ 133.322 Pa | |
| Bar | bar | = 105 Pa |
*Non-SI unit accepted by CGPM for use with the International System of Units [6]. The unmarked entries have no official sanction from CIPM or CGPM [6].
The symbol for litre is either L or l. ISO and IEC prefer l, because the term “litre” is not derived from the proper name of a person. L is preferred here to avoid confusion with the numeral 1 [5, 6]. Dalton is also termed unified atomic mass unit (symbol u); in Table 2, its standard uncertainty is indicated in the parentheses.
3 Prefixes for multiples and submultiples of units
Prefixes denoting decimal factors 10n have been defined [6] (Table 3). For convenience, the Commission on Clinical Chemistry of IUPAC and IFCC recommended a preference in the clinical laboratory for decimal factors with decimal prefixes in steps of a factor 1000 [3]. This selection of a decimal prefix often permits numerical results to be reported with a numerical value in the recommended interval between 0.1 and 999. For most purposes, the prefixes hecto, deca, deci, and centi can be avoided, though they have equal legal standing.
SI prefixes denoting multiples of units and submultiples of units. The variable n is the decimal exponent of the factor.
| Prefix with n ≥ 1 | Prefix with n ≤ –1 | ||||
|---|---|---|---|---|---|
| Term | Symbol | n | Term | Symbol | n |
| Yotta | Y | 24 | Deci | d | –1 |
| Zetta | Z | 21 | Centi | c | –2 |
| Exa | E | 18 | Milli | m | –3 |
| Peta | P | 15 | Micro | μ | –6 |
| Tera | T | 12 | Nano | n | –9 |
| Giga | G | 9 | Pico | p | –12 |
| Mega | M | 6 | Femto | f | –15 |
| Kilo | k | 3 | Atto | a | –18 |
| Hecto | h | 2 | Zepto | z | –21 |
| Deca | da | 1 | Yocto | y | –24 |
The prefix symbol and the unit symbol are combined without any space; a second prefix should be avoided; e.g., for picogram use pg, not p g or μμg. In units with a numerator and a denominator, multiple and submultiple shall be in the numerator; e.g., the number concentration of thrombocytes in blood should be expressed as 215 × 109/L (not 215 × 106/mL) and the substance concentration of arsenic in urine should be expressed as 41 nmol/L (not 0.041 nmol/mL).
Capital letters are used for the positive powers equal to or greater than mega. This avoids the confusion between mega (symbol M) and milli (symbol m), between peta (symbol P) and pico (symbol p), and between zetta (symbol Z) and zepto (symbol z).
4 Terminological rules of the NPU
To avoid misunderstandings, a set of rules is needed for transmission of data on properties:
The symbol for a kind-of-quantity is a single letter (Greek or Latin), printed in italic, with very few exceptions, for example, pH. For each kind-of-quantity, there is only one coherent SI unit. However, the same SI unit may be used to express the values of quantities with different kinds-of-quantity. Therefore, a unit cannot identify the kind-of-quantity; e.g., volumic mass and mass concentration use kg/L, so both the unit and the kind-of-quantity must be stated (see the NPU format above).
The symbol for a unit is represented by one, two, or three upright lower-case letters, except if the unit is termed after a person; e.g., A and K for ampere and kelvin, respectively, and the special case of L for litre. The term is still written with an initial lower-case letter. In the clinical laboratory, in expressions of volume, the litre and its submultiples are preferred to cubic metre and its submultiples.
The systematic term for a component should not be abbreviated, because abbreviations are not internationally accepted. In the NPU format, the initial letter of the component is a capital letter, except for some prefixes; e.g., T4 should be replaced by Thyroxine and α-Amylase is correct. Bacteria, viruses, fungi, plants, and animals including parasites should be designated by their taxonomic term. Terms for genera, species, and subspecies are printed in italic; terms for orders and families, and for strains or races, are printed in roman script; however, the IFCC databank uses roman script throughout for convenience [11]:
Urine(catheter)–Bacterium, nitrite producing; number concentration(procedure) = 2.3 × 106/L.
Expectoration–Bacterium; taxon = Mycobacterium tuberculosis.
The system and any modifiers may be abbreviated; e.g., Pt, B, P, U, a, f, v for patient, blood, plasma, urine, arterial, fasting, and venous, respectively.
An NPU code NPUXXXXX uses the NPU format for each of the 16 000 entries in the NPU databank [11, 12]. This code is well adapted to electronic health records or laboratory administrative systems.
NPU10547 Pt–Insulin(administered); substance content(i.v.; amount-of-substance/body mass) = 0.3 μmol/kg.
5 Membership of sponsoring bodies
Membership of the IUPAC Chemistry and Human Health Division Committee for the period 2014–2015 is as follows:
President: T. Perun (USA); Vice President: R. Cornelis (Belgium); Secretary: M. Schwenk (Germany); Titular Members: E. Differding (Belgium); J. Fischer (Hungary); V. Gubala (Slovakia); P. Illing (UK); L. Johnston (Canada); H. Møller Johannessen (Denmark); W. A. Temple (New Zealand); Associate Members: V. Abbate (UK); M. Kiilunen (Finland); Y. C. Martin (USA); S. Mignani (France); D. Rotella (USA); National Representatives: S. Alihodžić (Croatia); S. Bachurin (Russia); B. Haug (Norway); R. J.-R. Hwu (China/Taipei); R. Leurs (Netherlands); N. Nahar (Bangladesh); P. Ploypradith (Thailand); A. Rahatgoanker (India); G. B. Teh (Malaysia); M.-X. Wang (China/Beijing).
Membership of the IFCC Scientific Division for the period 2014–2015 is as follows:
President: I. Young (UK); Vice President: P. Gillery (France); Secretary: G. Myers (USA); Titular Members: C. M. Cobbaert (Netherlands); N. Hamasaki (Japan); G. Merlini (Italy); Corporate representatives and Consultants: J. Passarelli (USA); H. Schimmel (Belgium); D. Bunk (USA); M. M. Müller (Austria).
Article note
Sponsoring bodies: IUPAC Chemistry and Human Health Division. IFCC Scientific Division. See more details on p. 1929.
Acknowledgments
This paper is an extension of the joint IFCC-IUPAC project #2007-033-3-700. The authors wish to thank for the knowledgeable support of the members of the C-SC-NPU (IFCC & IUPAC): Ivan Bruunshuus (Alleroed, Denmark); Pedro de Araujo (Sao Paulo, Brazil); Robert Flatman (Chair, Taringa, Australia); Urban Forsum (Linköping, Sweden); Gilbert Hill (Toronto, Canada); Antonin Jabor (Kladno, Czech Republic); Jens Gledisch (Oslo, Norway); Helle Johannessen (Copenhagen, Denmark); Daniel Karlsson (Linköping, Sweden); Wolf Külpmann (Hannover, Germany); Ulla Magdal Petersen (Copenhagen, Denmark); Clement Mc Donald (Indianapolis, USA); Gunnar Nordin (Uppsala, Sweden); Henrik Olesen† (Copenhagen, Denmark); Françoise Pontet[†] (Paris, France); Gunther Schadow (Indianapolis, USA); and Kaoru Yamanouchi (Tokyo, Japan).
References
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