October 2019 ISSN 1650-3414 Volume 30 Number 3 Communications and Publications Division (CPD) of the IFCC Editor-in-chief: Prof. János Kappelmayer, MD, PhD Faculty of Medicine, University of Debrecen, Hungary e-mail: [email protected] The Journal of the International Federation of Clinical Chemistry and Laboratory Medicine In this issue Recommendations on measurement units – why and how Young Bae Lee Hansen 250 Evaluation of visual serum indices measurements and potential false result risks in routine clinical chemistry tests in Addis Ababa, Ethiopia Tigist Getahun, Anberber Alemu, Firehiwot Mulugeta, Merone Sileshi, Abenezer Ayalkebet, Wosene Habtu, Zeleke Geto, Fitsum Girma, Feyissa Challa, Mistire Wolde 276 Best practices in the implementation of a point of care testing program: experience from a tertiary care hospital in a developing country Aysha Habib Khan, Shahid Shakeel, Khairunnissa Hooda, Kashif Siddiqui, Lena Jafri 288 Prevalence of liver function test abnormality and associated factors in type 2 diabetes mellitus: a comparative cross-sectional study Getnet Teshome, Sintayehu Ambachew, Alebachew Fasil, Molla Abebe 303 Correlation of body mass index and waist/hip ratio with glycated hemoglobin in prediabetes Manju Bala, Meenakshi, Sameer Aggarwal 317 Hyperuricemia and its association with cardiovascular disease risk factors in type two diabetes mellitus patients at the University of Gondar Hospital, Northwest Ethiopia Birhanu Woldeamlak, Ketsela Yirdaw, Belete Biadgo 325 Atypical hemolytic uremic syndrome: genetic landscape challenge Laura Valiña, Bernardo López Andrade, Josep Miquel Bauça 340 Letter: Manchineel apple of death Michelle Muscat 346 This is a Platinum Open Access Journal distributed under the terms of the Creative Commons Attribution Non-Commercial License which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Recommendations on measurement units – why and how Young Bae Lee Hansen On behalf of the IFCC-IUPAC Committee on Nomenclature for Properties and Units (C-NPU) ARTICLE INFO ABSTRACT Corresponding author: Globally, laboratories are producing, communicating, Young Bae Lee Hansen (YBLH) Titular member of C-NPU and exchanging millions of laboratory examination The Danish Health Data Authority values to multiple parties every day. For most values, Ørestads Boulevard 5 ‘measurement units’ are required to make the nu- DK-2300 Copenhagen S. Denmark merical values comparable and meaningful. However, E-mail: [email protected] a non-systematic use of ‘measurement units’ can cre- ate errors in communication between health care pro- Key words: weights and measures, metric system, viders and become a risk to patient safety. Therefore, international system of units, health the Committee of Nomenclature for Properties and information interoperability, health Units (C-NPU) recommends using an unambiguous communication, medical informatics terminology of ‘measurement units’, for daily patient Disclosure: care and scientific publications. In this work, C-NPU The author declares no conflict of interest. summarizes the recommendations on ‘measurement units’, explaining the reasons and the principles of the ‘measurement units’ used in laboratory medicine. Page 250 eJIFCC2019Vol30No3pp250-275 Young Bae Lee Hansen Recommendations on measurement units – why and how INTRODUCTION have been implemented in the Nomenclature for Properties and Unit (NPU) terminology (4, 5). ‘Measurement unit’ (unit) is a well-understood and necessary concept in laboratory medicine. In this letter, we summarise the IFCC’s and IUPAC’s Without units, most quantitative laboratory -ex Recommendations and Technical Reports on amination values will not make sense and are relevant principles and rules on units in labora- not comparable. Dybkær and Jørgensen wrote tory medicine, and the reasons behind these in 1967: “To state that the mass concentration principles. of haemoglobin in a blood sample is 25 is essen- tially meaningless. If the unit g/L is assumed, KIND-OF-QUANTITY, QUANTITY, the patient is considered anaemic. If the unit g/ AND MEASUREMENT UNIT dL is assumed, the patient is considered to be In order to understand the concept ‘measure- polycytaemic” (1). ment unit’, it is necessary to see its close re- With the introduction of the International lation to the other essential metrological con- System of Units (SI units) (2) in the 1960’s, the cepts ‘kind-of-quantity’ and ‘quantity’. ‘Mass’, worldwide scientific laboratory societies have ‘substance concentration’, and ‘volume fraction’ accepted and, to a large extent, implemented are examples of ‘kinds-of-quantity’ that place the SI units for presentation of laboratory re- system and any relevant component in a mathe- ports in health care and research. However, matical relation. E.g., ‘substance concentration’ as indicated by the recent campaign of the is defined as “amount-of-substance of compo- European Federation of Clinical Chemistry and nent B divided by volume of system 1” or: laboratory Medicine (EFLM), there is never- Amount-of-substance of component B theless a further need of standardisation or Volume of system 1 harmonisation on a national, regional, and On a more tangible level, the system and com- international level (3). The campaign recom- ponent can be specified further including a mended implementation of the “principles on magnitude, e.g. : units”, proposed by Dybkær and Jørgensen in 1967 (1). These principles are more restricted Amount-of-substance of sodium ion = 140 mmol/L than the original SI-system to ensure unambi- Volume of Mr. Smith’s plasma guity in reporting, presenting, and exchanging The latter example is a ‘quantity’, having the for- quantity values in health care. Each laboratory mal and metrological definition “property of may choose any relevant units for reporting phenomenon, body, or substance, where the laboratory examination values, but when mul- property has a magnitude that can be expressed tiple parties are involved in exchanging labora- as a number and a reference” (6). The differ- tory reports, the choice should be limited to the ences between both concepts are shown in “principles on units”. Arguably, the principles Table 1. will reduce the risk of post-analytical errors, In laboratory medicine, eight ‘base kinds-of- e.g. misunderstanding and misinterpretation of quantity’ exist as listed in Table 2 with their laboratory reports and errors in communication corresponding ‘base units’ and ‘quantity di- between different health care personnel and mensions’ (5). The ‘base kinds-of-quantity (e.g. organisations. ‘amount-of-substance’) can be combined in var- The “principles on units” in laboratory medicine, ious ways, forming ‘derived kinds-of-quantity’, as initially proposed by Dybkær and Jørgensen, e.g. ‘substance concentration’. Page 251 eJIFCC2019Vol30No3pp250-275 Young Bae Lee Hansen Recommendations on measurement units – why and how Table 1 Kind-of-quantity and quantity Examples Level Concepts Verbal expression Mathematical expression kind-of- substance Amount-of-substance of component B Abstract quantity concentration Volume of system 1 substance concentration of sodium ion Amount-of-substance of sodium ion = 143 mmol/L Measurable quantity in Mr. Smith’s plasma Volume of Mr. Smith’s plasma is 143 mmol/L at 2:30 p.m. on 2nd May 2018. In the example for ‘quantity’, ‘plasma’ is the ‘system’, ‘sodium ion’ is the ‘component’ and ‘substance concentration’ is the ‘kind-of-quantity’. Also, there is a magnitude according to the definition of ‘quantity’, as compared with the example for ‘kind-of-quantity’ that does not have a magnitude. To ‘substance concentration’, the corresponding (or kind-of-nominal property) and, when rele- compound unit can be, e.g., mmol/L. To a (base vant, the unit for a given laboratory examination. or derived) kind-of-quantity, several corre- sponding units are possible. Examples of corre- GENERAL RULES FOR SI UNITS sponding units to ‘substance concentration’ are AND NON-SI UNITS ‘mol/L’, ‘mmol/L’, ‘µmol/L’, ‘nmol/L’, etc. A com- It is recommended to use units with unambigu- prehensive description of ‘kinds-of-quantity’ ous definitions, accepted by international scien- and ‘measurement units’ can be found in IFCC’s tific communities. Such units can be SI units and and IUPAC’s ‘Silver Book’ (5)–together with non-SI units. ‘kind-of-nominal-property (related to ‘nominal properties’ which have no magnitude). 1. Base SI units Reporting solely the numerical value and unit The definitions, symbols, and magnitudes of SI may not be sufficient information on the ex- units are traced to accepted international refer- amination because the possible corresponding ences (Table 2) (2). ‘kind-of-quantity’ to e.g., ‘g/L’, could be ‘mass Examples concentration’ or mass density’. Moreover, in order for the clinicians to assess the values of “The metre is the length of the path travelled laboratory examinations, especially laboratory by light in vacuum during a time interval of examination reports from other laboratories, 1/299 792 458 of a second” (2). it is essential to provide information about the “The second is the duration of 9 192 631 770 generic nature of the laboratory examinations. periods of the radiation corresponding to the Thus, C-NPU recommends to report, systemati- transition between the two hyperfine levels of cally, the system, component, kind-of-quantity the ground state of the caesium 133 atom” (2). Page 252 eJIFCC2019Vol30No3pp250-275 Young Bae Lee Hansen Recommendations on measurement units – why and how Table 2 Base kinds-of-quantity, corresponding base units, and dimensions Base kind-of-quantity Base unit Dimension Term Term Symbol Symbol length metre m L mass kilogram kg M time second s T electrical current ampere A I thermodynamic temperature kelvin K Θ amount-of-substance mole mol N luminous intensity candela cd J number of entities one 1 1 A list of base kinds-of-quantity and their corresponding base units and dimensions from IFCC’s and IUPAC’s ‘Silver Book’ (5). Note: ‘Number of entities’ is not an SI base kind-of-quantity but is used as a base kind-of-quantity in laboratory medicine. Note: From the year 2019, all seven SI base 3.