Le Systeme International D'unites
1988; King Faisal Specialist Hospital and Research Centre; Volume: 8; Issue: 4 Linguagem: Francês
10.5144/0256-4947.1988.237
ISSN0975-4466
Autores Tópico(s)Health Sciences Research and Education
ResumoEditorialLe Systeme International D'unites Peter B. HerdsonMB, ChB, BMedSc, PhD, FRCPA, FRACR Peter B. Herdson Professor and Chairman, Department of Pathology and Laboratory Medicine, King Faisal Specialist Hospital and Research Centre, P.O. Box 3354, Riyadh 11211, Saudi Arabia Search for more papers by this author Published Online:1 Jul 1988https://doi.org/10.5144/0256-4947.1988.237SectionsPDF ToolsAdd to favoritesDownload citationTrack citations ShareShare onFacebookTwitterLinked InRedditEmail AboutIntroductionWith this July 1988 issue, the Annals of Saudi Medicine adopts Le Systeme International d'Unites (SI units), which is the most up-to-date version of the metric system and replaces all earlier versions of that system. Most medical and scientific journals now use SI units, and from a journalistic point of view, the system has been comprehensively reviewed by Donald S. Young in his article entitled "Implementation of SI units for clinical and laboratory data: style, specifications, and conversion tables," which appeared in the Annals of Internal Medicine, 1987;106:114-29.In 1954, the General Conference on Weights and Measures adopted a rationalized system based on the meter, kilogram, second, ampere, degree, kelvin, and candela, and in 1960, this system was given the title Systeme International d'Unites. In 1977, the 30th World Health Assembly recommended that SI units be used in medicine, and now the system is used in many countries to report medical laboratory data.Conversion to SI units took place during the 1970s in countries of the European community and in Australia and New Zealand. In 1983, most of Canada converted, and currently SI units are being introduced in the United States to replace the various units that have been used until now to report laboratory information. In the United States, the action has been initiated by the Medical and Health Coordinating Group of the American National Metric Council and has been endorsed by many professional societies including the American Medical Association. In 1986, Kuwait became the first country in the Middle East to adopt SI units, and several hospital laboratories in the Kingdom of Saudi Arabia have moved or are in the process of changing to SI units.THE SI SYSTEMBriefly, the SI has seven base units (Table 1) from which other units are derived (Table 2). If only base units were used to report pathology data, some test values would be either unmanageably large or small. The SI uses decimal multiples or submultiples which change preferably by increments of 103 or 10-3, expressed by prefixes (Table 3). The factors are powers of 10, with exponents that are simple multiples of 3, to facilitate conversion of results in different units. Note that prefixes such as hecto (102), deca (101), deci (10-1), and centi (10-2) are not multiples of 3, and their use in science and medicine is discouraged.Table 1. Base units of SI.*Table 1. Base units of SI.*Table 2. Representative derived units.*Table 2. Representative derived units.*Table 3. Prefixes and symbols for decimal multiples and submultiples.*Table 3. Prefixes and symbols for decimal multiples and submultiples.*SI UNITS IN MEDICINEThe underlying reason for change to SI units is that biological reactants occur on a particle-to-particle basis. When all data are expressed in uniform units based on numbers of particles (molar concentrations), a better concept of the relative amounts of constituents of body fluids and reactants in biological processes is gained.Consider the following: Baby Abdullah, aged 7 days, has a serum bilirubin level of 20.0 mg/dL by the old system or 340 μmol/L in SI units and a serum albumin level of 4.0 g/dL by the old system or 580 μmol/L as expressed in SI units. With the old system of units, there appears to be 200 times as much albumin as bilirubin in this jaundiced baby. Yet when stated in molar terms (SI units), there is only 1.7 times as much albumin as bilirubin; the influence of albumin concentration on the binding of bilirubin and other components and the displacement of one compound by another are more apparent.The SI allows easier assessment of the relationships between different reactants in various metabolic cycles involving different classes of compounds, e.g., fats, amino acids, and carbohydrates. It also helps to assess the association of related compounds or metabolites in different tissues, e.g., hemoglobin in red blood cells and in plasma, bilirubin and iron in plasma, and urobilinogen in urine.WHY CHANGE?Although SI allows much easier assessment of interrelationships, there are still those in some countries who question the need for change. Obviously, the more countries and journals that have moved to SI units, the more the need for others also to change, to provide easy communication and uniformity. The immediate goal is to correct the present confused measurement system and improve test-result communication within and between countries. Here in the Kingdom of Saudi Arabia and in other Middle Eastern countries, there is the added incentive that with medical and allied professional staff from many different parts of the world–some of whom already are familiar with SI units, while others are used to a variety of units–there is much to commend our moving to a universal system.It has been decided to move entirely to SI units with this issue, having all papers converted to the Systeme. Some other journals have included old units along with SI units for a defined changeover period; although for the time being authors may list converted units in parentheses, we believe this may be more confusing, and we have an educational responsibility to help all physicians and allied health personnel become familiar with SI units as quickly and efficiently as possible. We know from experience that those laboratories which reported both old and SI units during a changeover period ran into far more problems than those which changed overnight–providing, of course, that all relevant personnel were issued conversion tables and that reference ("normal") ranges were given on all laboratory reports.Table 4 lists some common laboratory data in old and new (SI) units.Table 4. Representative laboratory data in SI units.Table 4. Representative laboratory data in SI units.PROBLEMSThere are several instances in clinical and laboratory medicine in which it is impossible or undesirable to change to SI units. The most obvious is the measurement of blood pressure, which will continue to be recorded as millimeters of mercury (mm Hg) rather than kilopascals (kPa). Analysis of enzyme concentrations poses particular problems, and these generally will continue to be reported in international units.In summary, the Annals now moves to SI units at an appropriate time in relation to the development of clinical and laboratory medicine and medical research in the Kingdom of Saudi Arabia and neighboring countries. Authors planning to submit manuscripts for possible publication in the Annals should consult "Information for Authors" concerning SI units and other important requirements. Next article FiguresReferencesRelatedDetails Volume 8, Issue 4July 1988 Metrics History Published online1 July 1988 InformationCopyright © 1988, Annals of Saudi MedicinePDF download
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