Editorials
Metrication fror Crawl to Walk
in this issue, by Peter
Lehmann, provides a summary of the
development and general concept of the
international metric system (SI), as well as
a compilation of normal values of commonly assayed body constituents in conventional and in SI units and a list of
conversion factors.
We recommended in an editorial published in this journal nearly three years
ago 1 that, after due consideration, we
should initiate a change to use of the SI,
concomitantly providing for an interim
period during which results would be reported in both new units and conventional
units. Since then, while Europe and
Australia have galloped ahead, American
medicine has been on the crawl. 2,3
In our opinion, the disadvantages of
proceeding (which were discussed in our
previous editorial and are discussed by
Bradley Copeland in the editorial that
follows this one) are now considerably
outweighed by the disadvantages of not
proceeding. American physicians are
already finding their access to European
medical journals—many of which are
published in English—seriously hampered
by unfamiliarity with the SI. Examples
come readily to hand. In Ramus and
Shorey's article on Crohn's disease, recently published in the British Medical
Journal,4 a patient's serum bilirubin at
time of hospital administration is given
as 140 jU.mol/1. How many of our American
readers immediately grasp the significance
of this concentration? Toft and associates,
in their recent article in The Lancet concerning thyroid function, 5 state that the sensitivity of the T3 assay was "0.25 nmol/1."
How many of you, reading this in the
United States, can readily assess the significance of this sensitivity? Europeans and
Australians, on the other hand, as they
forget normal values in conventional units,
will likewise be losing access to our medical literature unless we take positive action
T H E LEAD ARTICLE
Received and accepted October 30, 1975.
now. The situation is rapidly becoming
intolerable, detrimental to progress in
medicine, to the continuing education of
physicians and allied health workers; and
ultimately, of course, to the quality of patient care.
Therefore, in the instructions on new
editorial policy that appear in this issue,
future contributors are requested to express results of laboratory tests in SI units,
in parentheses, following the corresponding values in conventional units.
We will continue to face problems, of
course. Indeed, it has been necessary to
list in the instructions to contributors
those SI units that, for various reasons,
we do not yet recommend. For example,
acceptance of the proposed new unit of
enzymic activity (the katal) has been very
limited. Also, there is international agreement among hematologists not to convert,
at this time, to expression of hemoglobin
values in substance-concentration units.
For similar reasons we cannot recommend
expressing in substance-concentration
units any substance with unknown or incompletely known molecular weights. We
do not recommend abandonment of the
traditional "milliosmoles per liter" expression; and believe that, in many instances,
use of the unit "pH" may be preferable to
use of the substance-concentration term
for hydrogen ion. Finally, further work
is needed on appropriate use of significant
figures for values expressed in the new
units.
In spite of these caveats, it has clearly
become our responsibility to take the lead
in reuniting the presently separated halves
of the world's medical literature, and we
accept the responsibility.
MYRTON F. BEELER,
M.D.
New Orleans, Louisiana
References
1. Beeler MF, Copeland BE, Gambino SR, et al:
T h e metric system and clinical chemistry.
A m J Clin Pathol 59:277-281, 1973
20
A.J.C.P.—Vol.
EDITORIALS
2. Copeland BE, Beautyman W, Bradley R, et al:
Study Committee to Evaluate Changes in Units
of Clinical Chemistry Tests. N Engl J Med
293:20-44, 1975
3. Inglefinger FJ: Metrication on the crawl. N Engl
J Med 292:806-807, 1975
65
4. Ramus MI, Shorey SA: Crohn's disease and psoas
abscess. Br Med J 3:574-575, 1975
5. Toft ER, Irvine UJ, Seth J, et al: Thyroid function in the long-term
followup of patients
treated with iodine131 for thyrotoxicosis. The
Lancet. 11:576-578, 1975
SI Units—A Clarification
T H E GRAM a n d milligram ARE decimally
related SI units. Only t h e kilogram is an
SI unit. C u r r e n t units, such as g r a m p e r
liter, milligram p e r deciliter, a r e SI related
units.
" A d o p t i o n of SI u n i t s " d o e s not m e a n
c o m p u l s o r y a d o p t i o n of m o l e c u l a r conc e n t r a t i o n units.
Mass c o n c e n t r a t i o n units a n d molecular c o n c e n t r a t i o n units a r e BOTH SI r e lated units.
T h e C o n f e r e n c e G e n e r a l d e Poids et
M e s u r e (CGPM) has not r e c o m m e n d e d
that clinical chemistry units be c h a n g e d
from mass c o n c e n t r a t i o n to m o l e c u l a r
c o n c e n t r a t i o n . O n l y t h e C G P M can issue
official s t a t e m e n t s r e g a r d i n g SI units.
T h e official U.S. publication is N B S
Special Publication # 3 3 0 , T h e I n t e r n a tional System of Units (SI), 1974.
Dr. C. H . Page (NBS USA) is C o o r d i n a t o r for I n t e r n a t i o n a l S t a n d a r d i z a t i o n
Activities. D r . E. A m b l e r is t h e U . S . m e m b e r
of C G P M .
S o m e g r o u p s , both national a n d international, r e c o m m e n d molecularization of
all clinical chemistry units. O t h e r g r o u p s
d i s a g r e e with this for various reasons.
D i s a g r e e m e n t is consistent with scientific
discussion.
T o imply t h a t only SI molecular units a r e
acceptable u n d e r t h e SI system is incorrect a n d unscientific.
At the N i n t h World C o n g r e s s of Societies
of Pathology, Sydney, Australia, 1975, t h e
following resolution was a d o p t e d by t h e
Commission on World S t a n d a r d s .
Commission on World Standards
World Association of Societies of Pathology
Resolution No. 2: T o Clarify the
Discussion of SI Units
WHEREAS the general public as well as the
Received and accepted November 14, 1975.
entire scientific community are
urged to adopt the SI system
of units moved that the Commission on World Standards (in
order to clarify the understanding of the SI unit system)
agrees (1) that both the mass concentration
unit (g/L) and the substance concentration unit (mol/L) are included in the SI unit system
(2) that it is not correct to imply that
conversion to or adoption of the
SI system requires the adoption
of the mol concentration unit as
the only concentration unit.
B R A D L E Y E. C O P E L A N D ,
Boston,
M.D.
Massachusetts
EDITOR'S N O T E
T H E MEMBERS of t h e B o a r d of Editors have
u r g e d t h a t t h e I n t e r n a t i o n a l Metric System
(SI) be i n t r o d u c e d in t h e American Journal
of Clinical Pathology in o r d e r to familiarize
o u r r e a d e r s with SI a n d to m a k e the J o u r n a l
m o r e r e a d a b l e in c o u n t r i e s now u s i n g SI.
I n the n e a r f u t u r e in t h e A J C P , q u a n t i t a tive m e a s u r e m e n t s in t h e conventional
units will be followed by SI in p a r e n t h e s e s .
T h i s will apply to quantitative m e a s u r e m e n t s with t h e exception oipH, gas p r e s s u r e m e a s u r e m e n t s (P 0 2 a n d Pco2)> a n d
osmolality, w h e r e t h e c u r r e n t l y used units
m a y be r e t a i n e d . All c o n c e n t r a t i o n s s h o u l d
be based o n a v o l u m e of o n e liter a n d
a m o u n t s e x p r e s s e d as moles e x c e p t in those
cases w h e r e definite m o l e c u l a r weights
have n o t b e e n established, e.g. p r o t e i n s , a n d
m i x t u r e s , w h e r e the use of SI units is o p tional. C o n v e r s i o n may be c a r r i e d o u t u s i n g
factors given in Dr. L e h m a n n ' s p a p e r . Presently used e n z y m e units s h o u l d be r e t a i n e d .
A u t h o r s a r e u r g e d to s u b m i t their m a n u scripts in this f o r m h e n c e f o r t h .
FRANK VELLIOS,
Editor
M.D.