Recommendations for clinical laboratory science reports regarding properties, units, and symbols: the NPU format1)

Georges Férard; René Dybkaer

doi:10.1515/cclm-2012-0769

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Recommendations for clinical laboratory science reports regarding properties, units, and symbols: the NPU format¹⁾

Georges Férard und René Dybkaer

Veröffentlicht/Copyright: 4. Januar 2013

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Abstract

The document describes the Nomenclature for Properties and Units (NPU) format developed by the joint committee on Nomenclature for Properties and Units of the IFCC and IUPAC. Basic concepts, in particular system, component, kind-of-property, and unit are defined. Generalities concerning quantities and units, and terminological rules are recalled. A constant format is structured for reporting clinical laboratory information. It is adapted for examinations, including measurements, performed in the clinical laboratories. The NPU format follows international recommendations. Using this format, more than 16 000 properties examined in the clinical laboratories have been described. A regularly updated version of the descriptions is available from the IFCC. Examples from different disciplines are given to promote the dissemination of the format. The object of the NPU format is the transfer of examination data without loss of accuracy between the laboratory personnel and the clinicians. The format is well-adapted for comparative and epidemiological studies.

Keywords: information exchange; laboratory report; property; terminology; unit

Introduction

The terminology of Nomenclature for Properties and Units (NPU) aims at describing properties, including quantities, examined in clinical laboratories for a patient. It was originally jointly approved in 1966 by International Union of Pure and Applied Chemistry (IUPAC) and by International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) [1] 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) [2], the International Vocabulary of Metrology (VIM) [3], and also to ‘An outline for a vocabulary for nominal properties and nominal examinations – Basic and general concepts and associated terms’, recently prepared by the IFCC and IUPAC NPU committee [4].

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 via this comprehensive summary the proper NPU terminology for reliable exchange of patient examination data between laboratories and clinicians. Currently, a databank managed by the IFCC contains more than 16 000 entries describing properties examined in the clinical laboratories, according to a structured format comprising three elements: System, Component, and kind-of-property. Some examples in the NPU format are included. The NPU format is also well-adapted for comparative and epidemiological studies. The use of this syntax and SI units enables the translation of these descriptions into other languages without loss of meaning or accuracy. More information is found in the IUPAC and IFCC ‘Silver Book’ [5].

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) =

Further explanation is given below.

NOTE — In the IFCC & IUPAC database, all the entries use abbreviations for system, kind-of-property as well as specification. Also no numerical values are given, only a unit when relevant.

system: part or phenomenon of the perceivable or conceivable world consisting of a demarcated arrangement of a set of components and a set of relationships or processes between these components (modified from reference [6])

NOTE — In human biology, it may be the patient or a body part of the patient or the immediate surroundings.

Examples: Person, Blood, Urine, Kidney, Beta cells of the pancreas, Exhaled air.

NOTE — In the NPU format, the initial letter of the term for a system is a capital.

component: part of a system [6]

NOTE — The component may be a physical part of the system, a chemical or biochemical compound, or a process.

Examples: Calculus, Glucose, Intestinal absorption, Cortisol secretion

NOTE — In the NPU format, the initial letter of the term for a component is a capital.

kind-of-property: aspect common to mutually comparable properties

NOTE 1 — The term is hyphenated to demonstrate that the phrase is a single term.

Examples: number concentration (C), volume (V), amount-of-substance (n), substance concentration (c), catalytic-activity concentration (b), taxon, colour, sequence variation

NOTE 2 — The definition is analogous to that of ‘kind of quantity’ in the VIM [3].

dedicated kind-of-property: kind-of-property with given sort of system and any pertinent sorts of component [6]

Examples: mass of a patient, substance concentration of glucose in plasma.

property: inherent state- or process-descriptive feature of a system including any pertinent components [6]

NOTE — The terms “attribute”, “characteristic”, and “trait”, are sometimes used as synonyms of “property”.

Example: Patient(Urine)–Glucose; substance rate(procedure) = 8 mmol/d

First efforts at the standardisation of data transmission in clinical laboratories concerned quantities, i.e., those properties that have a magnitude, mostly expressed by a number and a unit [1]. However, many important properties of a classificatory nature such as species of microbes or genetic structure are inherently devoid of magnitude. The concept ‘property’ can be generically divided in many ways according to purpose. A possibility (relevant here) is to distinguish different types of property according to their algebraic characteristics [6]. Following this approach, nominal, ordinal, differential, logarithmic differential, and rational properties are distinguished:

nominal property: property of a phenomenon, body, or substance, where the property has no magnitude [3]

NOTE — A nominal property may be defined by an examination procedure, and can be compared for identity with another property of the same kind-of-property.

Example: Urine–Neuroleptic drug; taxon(procedure) = chlorpromazine

ordinal property, ordinal quantity: property, defined by a conventional measurement procedure, for which a total ordering relation can be established, according to magnitude, with other quantities of the same kind, but for which no algebraic operations among those quantities exist [3]

Example: Urine–Bilirubins; arbitrary concentration (procedure) = 2

NOTE 1 — The term ‘procedure’ refers to the measurement procedure. As the scale will depend on the local procedure, this procedure should be indicated in the report.

NOTE 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 [6]

Example: Patient–Body; temperature = 37.8°C

NOTE — ISO 80000-1 specifies a space between the numerical value and the unit symbol \xb0C [7], but this is against CCLM editorial policy. When the measurement scale consists of logarithmic values, the property may be specified as a logarithmic differential property.

Example: Urine–Hydrogen ion; pH(procedure) = 5.9

rational property, rational quantity: property having a magnitude and that can be divided by another property of the same kind-of-property [6]

Example: 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 [3]

NOTE — 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 ([3], but modified by inserting hyphens in the term)

NOTE 1 — Each kind-of-quantity may be designated by a term or a symbol.

Examples: length (l) and mass concentration (ρ)

NOTE 2 — A given kind-of-quantity may have synonyms and also different symbols. A given symbol is sometimes used for different kinds-of-quantity.

Synonyms: relative molecular mass and molecular weight [deprecated by the International Organization for Standardization (ISO)]
Symbols: A and S are recognised symbols for area and A is the recognised symbol for the following kinds-of-quantity: area, nucleon number, Helmholtz free energy, affinity of chemical reaction, absorbance.

NOTE 3 — The concepts here termed ‘kind-of-quantity’ are generally termed ‘quantity’ by Conférence Générale des Poids et Mesures (CGPM) [2], Bureau International des Poids et Mesures (BIPM) [3], and ISO 80000–1 [7].

To avoid ambiguity, it is recommended to use the NPU format (see above) for the presentation of a property in clinical laboratory sciences.

quantity of dimension one, dimensionless quantity: quantity for which all the exponents of the factors corresponding to the base quantities in its quantity dimension are zero [3]: L⁰M⁰T⁰I⁰Θ⁰J⁰N⁰ = 1

NOTE — 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

Example: Erythrocytes(Blood)—Reticulocytes; number fraction = 6 × 10^–3 = 0.6 % = 6 ‰

NOTE — ISO 80000–1 accepts per cent with the symbol % for the unit 0.01, and per mille with the symbol ‰ for the 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

Example: 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

Example: Plasma–Coagulation factor XI; relative substance concentration(immunological; actual/norm; procedure) = 0.80 = 80 %

arbitrary kind-of-quantity: kind-of-quantity outside the ISQ

NOTE 1 — There is no dimension or SI unit involved.

Example: Thrombocytes(Blood)–Aggregation, collagen-induced; arbitrary activity(normal; lightly weakened; weakened; utmost weakened; procedure) = lightly weakened

NOTE 2 — This example has an ordinal kind-of-quantity.

Generalities concerning quantities and units

‘Kinds-of-quantity’ are used to classify quantities of the same kind.

NOTE 1 — Quantities of the same kind within a given system have the same dimension.

NOTE 2 — Different kinds-of-quantity may also have the same dimension, e.g., substance content (n_B/m_system), and molality (n_B/m_solvent) have the dimension NM^–1 and the coherent SI unit mol/kg.

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 independent of other base kinds-of-quantity in a system of kinds-of-quantity (Table 1). The rest are derived kinds-of-quantity and are using either 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.

Example: The dimension of amount-of-substance is represented by N (Table 1).

Table 1

Base kinds-of-quantity, base units, and their dimensional symbols in the ISQ and SI. Although usually ignored in statements about the ISQ, ‘number of entities’ is a base kind-of-quantity.

Base kind-of-quantity		Base unit		Dimension	Date^a
Term	Symbol	Term	Symbol	Symbol
number (of entities)	N	one	1	1
length	l	metre	m	L	1889
mass	m	kilogram	kg	M	1889
time	t	second	s	T	1956
electrical current	I	ampere	A	I	1948
thermodynamic temperature	T, Θ	kelvin	K	Θ	1954
amount-of-substance	n	mole	mol	N	1971
luminous intensity	I_{_v}	candela	cd	J	1948

^aDate for the first adoption by CGPM.

NOTE 1 — Amount-of-substance should not be termed ‘number of moles’.

NOTE 2 — The kind-of-quantity amount-of-substance is proportional to the number of entities that must be specified and may be atoms, molecules, ions, electrons, other particles or specified groups of such particles [2].

Example: Urine–Nitrogen(N); amount-of-substance(procedure) = 360 mmol

NOTE 3 — The amount-of-substance does not equal number of entities but corresponds to number of entities. The relationship is governed by the Avogadro constant n_B = N_B/L = N_B/N_A.

NOTE 4 — The abbreviation of ‘amount-of-substance’ in derived kind-of-quantity terms is ‘am.s.’ in the IFCC & IUPAC Silver Book [5] and “‘amount’ in the IUPAC Green Book [8].

NOTE 5 — The symbol for ‘litre’ is either L or l. ISO and IEC prefer l, because it is not derived from the proper name of a person. L is preferred here to avoid confusion with the numeral 1 [5].

Some derived kinds-of-quantity, and their derived coherent units in the SI

Coherent derived SI units can be defined as products of the base units with no other proportionality factors than one. Examples are given in Table 2. Some symbols have several meanings. If so, they may be distinguished by subscripts or by different types of character.

Examples: A_r is the symbol for relative atomic mass, and A_m is that for molar radioactivity. N is the dimensional symbol of amount-of-substance, and N is the symbol of the unit newton.

Table 2

Some derived kinds-of-quantity, and their coherent units of the SI with special terms or symbols.

Kind-of-quantity		Unit		Definition in SI base units
Term	Symbol	Term	Symbol
frequency	f, ν	hertz	Hz	s^–1
radioactivity	A	becquerel	Bq	s^–1
massic energy of ionising radiation absorbed	D	gray	Gy	m² s^–2
massic energy equivalent of ionising radiation absorbed, dose equivalent	H	sievert	Sv	m²s^–2
force	F	newton	N	kg m s^–2
pressure, stress	p	pascal	Pa	kg m^–1 s^–2
energy, work, amount-of-heat	E, Q_{_e}	joule	J	kg m^–2 s^–2
power, energy rate	P, Φ_{_e}	watt	W	kg m² s^–3
electrical charge	Q	coulomb	C	A s
electric potential difference	U, V	volt	V	kg m² A^–1 s^–3
electric resistance	R	ohm	Ω	kg m² A^–2 s^–3
Celsius temperature	t, ϑ	degree Celsius	°C	K
catalytic activity	z	katal	kat	mol s^–1

NOTE 1 — The unit for Celsius temperature, i.e., the degree Celsius (symbol °C), is equal in magnitude to the kelvin (symbol K), the unit of thermodynamic temperature.

NOTE 2 — The term ’katal’ and symbol ‘kat’ for the SI coherent derived unit for ‘catalytic activity’ have been recognised by IUPAC, IFCC, International Union of Biochemistry and Molecular Biology (IUBMB), World Health Organization (WHO), and General Conference on Weights and Measures (CGPM) [2]. IUPAC & IFCC [9] 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

Example: Plasma–Aspartate transaminase; catalytic concentration(IFCC 2002) = 2.2 ×10^–6 kat/L or 2.2 μkat/L

NOTE 3 — A specification regarding the measurement procedure used is necessary when catalytic activity is involved, here ‘IFCC 2002’.

NOTE 4 — If the symbol U is still 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 [2]) in expressing biological activity of certain substances that cannot yet be defined in terms of the SI.

Example: Plasma–Insulin; arbitrary substance concentration(IRP 66/304; procedure) = 120 × 10^–3 IU/L

where IRP stands for International reference preparation of the WHO.

Multiples and submultiples of units

For use with SI units, decimal multiples and submultiples have been elaborated (Table 3), [9]. Correct 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.

Table 3

SI prefixes denoting decimal factors, 10ⁿ; m, exponent of 10³.

Term	Symbol	n	m
yotta	Y	24	8
zetta	Z	21	7
exa	E	18	6
peta	P	15	5
tera	T	12	4
giga	G	9	3
mega	M	6	2
kilo	k	3	1

hecto	h	2
deca	da	1
deci	d	–1
centi	c	–2

milli	m	–3	–1
micro	µ	–6	–2
nano	n	–9	–3
pico	p	–12	–4
femto	f	–15	–5
atto	a	–18	–6
zepto	z	–21	–7
yocto	y	–24	–8

In units, with a numerator and a denominator, multiple and submultiple shall be in the numerator. Compound prefixes shall not be used (nL, not mμL) [7].

For convenience, the Commission on Clinical Chemistry of IUPAC and IFCC recommended a preference in the clinical laboratory for decimal factors and decimal prefixes in steps of a factor 1000 [1]. For most purposes, the prefixes hecto, deca, deci and centi can be avoided (Table 3, separated by broken lines), though they have equal legal standing.

The prefix symbol and the unit symbol are written without any space.

Note the use of capital letters for the positive powers from mega. This avoids the confusion between mega (symbol M) and milli (symbol m), and between peta (symbol P) and pico (symbol p).

3.3 Non-SI units

Several non-SI units are widely used in clinical laboratory sciences. Some are listed in Table 4 with the corresponding value in SI unit. When non-SI units are used, it is recommended to indicate the conversion factor to the SI.

4 Terminological rules of the NPU

To avoid misunderstandings, a set of rules is needed for transmission of data on properties.

Table 4

Examples of non-SI units.

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^a	L, l	= 10^–3m³
mass	dalton^a	Da	= 1.660 538 86×10^–27 kg
time	minute^a	min	= 60 s
	hour^a	h	= 3 600 s
	day^a	d	= 86.4×10³s
	week	w	= 604.8 ×10³s
pressure	millimetre of water	mmH₂O	= 9.806 65 Pa
	millimetre of mercury	mmHg	≈ 133.322 39 Pa
	torr	Torr	≈ 133.322 39 Pa
	bar	bar, b	= 10⁵ Pa

^aNon-SI unit accepted by CGPM for use with the International System of Units.

The symbol for a kind-of-quantity is a letter (Greek or Latin), printed in italic (Tables 1 and 2).

NOTE 1 — 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.

Examples: volumic mass and mass concentration use kg/L; osmolarity and substance concentration use mol/L.

For that reason, it is important to combine the designation of the unit and of the kind-of-quantity as it is prescribed in the NPU format for the expression of a value (see NPU format above).

NOTE 2 — The term for a kind-of-quantity may be abbreviated. A list of English-language abbreviations for kinds-of-quantity is available in the NPU databank [10]. Thus am.s., cat., c., cont., fr., num., pr., rel., subst., vol. for amount-of-substance, catalytic-activity, concentration, content, fraction, number, pressure, relative, substance, volume, respectively. They can be combined: subst.c. for substance concentration.

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 (Table 1) and the special case of L for litre. In this case, the term is still written with an initial lower-case letter; only the unit symbol has an initial capital.

NOTE 1 — A is the symbol for several kinds-of-quantity: decadic absorbance, area, radioactivity, and affinity of chemical reaction. Subscripts may be added to avoid confusion.

Example: A₁₀ for decadic absorbance [8]

Many other examples may be found in two IUPAC colour books [5, 8], and the ISO/IEC 80000 series [7].

NOTE 2 — In the clinical laboratory, in expressions of volume, the litre and its submultiples are preferred to cubic metre and its submultiples. In expressions of concentrations, submultiples of the litre should not be used in the denominator. For example, the number concentration of thrombocytes in blood should be expressed as 215× 10⁹/L (not 215×10⁶/mL).

The systematic term for a component should not be abbreviated, because abbreviations are not internationally accepted, are not interdisciplinary, and may cause inconvenience and waste of time for staff, and sometimes danger to the patient.

Example: Creatine kinase is used instead of CK.

NOTE 1 — In the NPU format, a prefix may be in lower case, if that is the usual form.

Example: α-Amylase

NOTE 2 — In the NPU format, bacteria, viruses, fungi, plants, and animals including parasites should be designated by their taxonomic term. Terms for genera, species, and subspecies are printed in roman; terms for orders and families, and for strains or races should be printed in italic, but the IFCC & IUPAC database uses roman script for all, because italic characters are not always available.

Example: Urine(catheter)–Bacterium; number concentration(procedure) = 2.3 ×10⁶/L

The term for a system may be abbreviated and specified. A list of English-language abbreviations or codes has been established for commonly used systems in the human body [5, 10]. Thus Pt, B, P, U, DNA may be used for the systems Patient, Blood, Plasma, Urine, Deoxynucleic acid, respectively. Other abbreviations have been proposed for other languages.

As a more concise presentation, a NPU code NPUXXXXX is also available for each of the current 16 000 entries of the IFCC NPU databank [11]. This code is well-adapted to electronic health records or laboratory administrative systems.

Table 5

Examples of specifications that may be added in parentheses in the NPU format.

System	Component	Kind-of-property	Type of property
Faeces	Virus	taxon(procedure)	nominal
Secretion(trachea)	Streptococcus pneumoniae(DNA)	arbitrary concentration(procedure)	ordinal
Patient	Blood	temperature(procedure)	differential
Plasma(aBlood)	Hydrogen ion	pH(37°C)	logarithmic differential
Plasma	Calcium(free)	substance concentration(pH = 7.40; procedure)	rational
Plasma	Alanine transaminase	catalytic concentration(IFCC 2002)	rational

The abbreviation ‘a’ in Plasma (aBlood) means ‘arterial’.

Example: NPU10547 Pt—–Insulin(administered); substance content(i.v.; amount-of-substance/body mass) = 0.3 μmol/kg

Corresponding author: Georges Férard

Thanks go to all the members of the IFCC and IUPAC working group for the revision of the Silver Book ‘Compendium of Terminology and Nomenclature of Properties in Clinical Laboratory Sciences (1995)’: Xavier Fuentes-Arderiu, Gilbert Hill, Dongchong Kang, Clem McDonald, Françoise Pontet, Anders Thor (†), and to Ulla Magdal Petersen and Helle Møller Johannessen.

Conflict of interest statement

Authors’ conflict of interest disclosure: The authors stated that there are no conflicts of interest regarding the publication of this article.

Research funding: None declared.

Employment or leadership: None declared.

Honorarium: None declared.

¹⁾
Dedicated to two important actors in the field of standardization: Anders J. Thor (deceased on 7 April 2012) and Henrik Olesen (deceased on 15 April 2012).

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Received: 2012-6-27

Accepted: 2012-11-12

Published Online: 2013-01-04

Published in Print: 2013-05-01

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https://doi.org/10.1515/cclm-2012-0769

Schlagwörter für diesen Artikel

information exchange; laboratory report; property; terminology; unit