Editorial
On the Matter of Units—An
THE PUBLICATION in this issue of the Journal
of the Statement from the Third Quadrennial International Symposium on Quantities and Units in Clinical
Medicine (Paris, 14th and 15th November 1980) is a
reminder that the question of units to be used for reporting quantitative data in medicine is still under discussion. The Symposium, organized by the Commission
on World Standards of the World Association of Societies of Pathology (COWS/WASP), serves as perhaps the only international forum where these specific
matters are discussed by representatives of the organizations that determine the basic standards and units
(ISO, BIPM), the organizations that made the recommendations on quantities and units for use in clinical
chemistry, and hence, by extrapolation, in clinical medicine (IUPAC, IFCC), and the medical user organizations (COWS/WASP, ICSH, IUIS, WHO, WMA).
Some of the items discussed, particularly the use of
substance or mass concentrations (§3), are moot in
many countries where substance concentrations are already in use, or planned. Other items, such as the unit
for catalytic (enzyme) activity (§5), the unit for pressure (§7.2), or how to express particle concentrations
(§8-2.4), are still under active discussion by international standards organizations. A recommendation on
particle concentrations is currently in the final stage of
preparation by Commission on Quantities and Units in
Clinical Chemistry (IUPAC) and the Expert Panel on
Quantities and Units (IFCC), and is to be presented
for comment and discussion to the International Committee for Standardization in Hematology (ICSH), and
others, before January 1982. With regard to the use of
SI unit for pressure, the pascal, particularly for blood
pressure measurement, the 34th World Health Assembly in May 1981 recommended "that the millimetre of
mercury and the kilopascal be used simultaneously until
a future World Health Assembly considers the retention
of the millimeter of mercury unnecessary for the undisturbed delivery of health care and the interchange
of scientific information".
Update
mittee on Quantities and Units, within the Area
Committee on Clinical Chemistry, in order to obtain
a consensus, at least among clinical laboratory scientists, on the implementation of the provisional version
of Recommendation 1978 (Recommendation 1973,
published in 1974). The report, published in 19792 recommended a three stage conversion procedure: a) immediate (to begin in January 1980) use of substance
concentrations for quantities which would retain their
numerical values on conversion (e.g. univalent ions), b)
conversion, over a ten year period, to substance concentration (based on the volume of one liter) for analytes having known molecular masses, and c) consideration of all other quantities and units (e.g. pascal for
pressure, katal for enzyme activity) on an individual
basis. The provisional recommendations, without the
implementation timetable, were adopted by NCCLS at
their meeting in May 1981. The proposed timetable was
abandoned primarily because, in 1979, the American
Medical Association and the American National Metric
Council sponsored a meeting of representatives from a
number of medical disciplines to discuss the adoption
and implementation of "SI Units" in medicine. This
group, which in 1980 became the Medical and Health
Coordinating Group, American National Metric Council, is charged with producing a plan for the implementation of units for reporting quantitative data in
clinical medicine based on Recommendation 1978. The
Medical and Health Coordinating Group is now proceeding with this task.
The Medical and Health Coordinating Group is, perhaps, unique among all groups that have discussed
quantities and units in clinical medicine over the past
15 years in that it contains representation and input
from most of the clinical disciplines, as well as from
organizations representing the basic medical sciences,
medical educators, nursing and the allied health professions, and also the health care product manufacturing
associations. Thus, the final proposals will represent the
widest consensus of the health care professionals on this
topic.
The objective of the original proposal for the use of
units based on the SI for reporting clinical laboratory
data was to have a standardized set of units to replace
the plethora of units then in use, and to ensure that
In the United States there is, as yet, no agreement
as to how to proceed with the implementation of
IUPAC/IFCC Recommendation 19781 in clinical medicine. In 1975 the National Committee on Clinical Laboratory Standards (NCCLS) established a Subcom-
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A.J.C.P. -January 1982
EDITORIAL
such a set of units would conform to those being recommended by metrologists, and being adopted and used
by basic scientists. In the 15 years that have elapsed
since the original proposals the introduction of modern
technology into medicine has proceeded at a rapid pace.
Thus, for example, computerized axial tomography is
used, almost routinely, to enable clinicians to seek lesions in soft tissue, complementing the traditional visualizing technics of X rays and radionuclide scans,
while surgeons using laser technology are able to
achieve pin point (and maybe in the future "cell point")
accuracy in surgical procedures. The clinical laboratory
has also adopted new technologies over the past few
years that enable clinical laboratory scientists to examine specific molecules within cells (fluorescent microscopy), to quantitate analytes accurately and precisely at concentrations several orders of magnitude less
than those traditionally reported (immunoassays) and
to quantitate (count) binding sites on cell surfaces for
substances to be taken up by the cells (receptor assays).
We appear, therefore, to have entered the era of molecular medicine (of molecular biology in the 1950s and
1960s) in which the application of basic research findings and techniques to clinical use for patient care is
providing to be highly effective. In such an environment
it is appropriate that active discussions on units are
taking place at the national (Medical and Health Coordinating Group) and international (COWS/WASP)
level. It is to be hoped that such discussions will lead
to a timely consensus on the units to be adopted for
quantitative studies in medicine, and that these will be
consistent with those used by basic and applied scientists whose information and technology are finding increased use in clinical medicine.
References
1. International union of pure and applied chemistry and international federation of clinical chemistry. Approved recommendation (1978)—quantities and units in clinical chemistry. Clin
Chim Acta 96:157F-183F, 1979. List of quantities in clinical
chemistry. Clin Chim Acta 96:185F-204F, 1979.
2. NCCLS proposed position paper: PPC-11, quantities and units:
SI. National committee for clinical laboratory standards, Villanova, PA 1979.
H. PETER LEHMANN, PH.D.
MYRTON F. BEELER, M.D.
Abbreviations used: ISO—International Organization for Standardization, BIPM—Bureau International des Poids et Mesures,
IUPAC—International Union of Pure and Applied Chemistry, I FCC—
International Federation of Clinical Chemistry, ICSH—International
Committee on Standardization in Hematology, IUIS—International
Union of Immunological Societies, WHO—World Health Association, WMA—World Medical Association.
NEWS AND NOTICES
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