Letters to the Editor:
The Metric System and Clinical Chemistry
To the Editor:—In view of the importance
of your editorial, "The Metric System and
Clinical Chemistry," 1 written by a special ad
hoc committee, we hope you will permit
some comments by the authors repeatedly
referred to.
As regards the names of the base units for
length and mass, the official English and
American spellings now are "metre" (as
given in the editorial) and "kilogram,"
respectively. 5
The "derived quantity of force" is not the
newton (N), but this coherent SI unit is used
in the measurement of force. In general
(algebraic) operations on quantities are independent of the system of units.
Interpretation of cm 3 as equal to 10~2m3
ignores the ISO rule, 5 which states that exponents in units apply to the whole unit,
including factors; thus, 1 cm 3 = 1 (cm) 3
= (10-2 m) 3 = 10"6 m 3 .
T h e p r e d i c a m e n t of clinicians confronted with new types of information always is a problem, but in this connection has
been overcome in other countries by public
relations work and the good practice of stating reference intervals ("normal values")
along with the measured values.
For biological reasons of comparison, it is
advantageous to give substance concentrations of metabolites (including glucose) instead of mass c o n c e n t r a t i o n s . Also,
amounts and concentrations of substances
(including drugs) entering or leaving the
organism preferably should be stated in
"molecular" kinds of quantities. The example of "a 50% glucose solution" is illustrative. Some would infer that 100 g of solution contained 50 g of glucose (C6H12O6);
most clinical chemists and biochemists
would take it to mean that 100 ml of solution contained 50 g of C6H12O6, while most
pharmacists would know that the 50 g are
(Key words: Metric system; Clinical chemistry.)
C6H12O6, H2O. T h e need to state the quantity also by concentration is obvious—here
the kind of quantity is mass concentration.
Indication of a formula unit is necessary
when mass-based kinds of quantities are
employed. In an emergency situation one
would inject the usual volume of the strong
glucose infusion fluid.
It is correctly pointed out that the choice
of "litre" as the preferred unit of volume is
a sad departure from coherency; this was
made because of chemical practice. It
should be noted that the "litre" (1) is identical to 10~3 m 3 and that it is now classified by
the International Committee of Weights
and Measures as a "unit in use with SI." A
later change together with the chemists to
cubic metre (perhaps symbolized by a single
letter) would hardly be "a debacle not
lightly to be considered," as the significant
figures would be unaltered: 1 mg/1 = 1
g/m 3 .
It has not been advocated to abandon
what "concentration expressions as milliequivalents per liter and milliosmoles per
liter" usually stand for, but only the misuse
and ambiguity of the units mEq/1 and
milliosmol/1. T h e IFCC/IUPAC recommends that the kind of quantity name
should be stated a n d the c o m p o n e n t
defined adequately. Thus, e.g., "S—Calcium ion(positive charge), substance concentration" makes superfluous the kind of
quantity "electroequivalent concentration."
"Osmolarity" and "osmolality," and the
so-called unit "osmol," have not been
uniquely defined. The substance concentration or molality of formal particles can
always be stated in mol/1. It is noteworthy that the IUPAC Division of Physical
Chemistry ignores such concepts and
"units" as "equivalent" and "osmole." 4
pH and substance concentration of hydrogen ion in blood are both useful, but
quite different types of quantities and sys-
306
February 1974
307
LETTERS T O T H E EDITOR
terns of diagnosis and treatment have been
built on either. The recommendations 2,3 do
not choose between them. The dimensionless kind of quantity, pH, is defined operationally by IUPAC 4 ; the corresponding
unit is unity.
C o n c e r n i n g "catalytic a m o u n t " and
"katal," it would be too much to expect that
any unit could lead to "interlaboratory
comparability of enzyme assay results"
based on measurement of an activity.
We are grateful to the Ad Hoc Committee on Nomenclature, Quantities, and Units
of Measure for its thorough review of the
IUPAC/IFCC tentative recommendations.
This kind of open and helpful discussion is
essential to mutual understanding—and
better recommendations.
R. D Y B K ^ R , M . D .
Department of Clinical Chemistry
Geriatric Unit
De Gamles By
DK-22oo Copenhagen N
Denmark
K. J0RGENSEN, M.D.
Department of Clinical Chemistry
Rigshospitalet
DK-21oo Copenhagen 0 , Denmark
References
Ad Hoc Committee on Nomenclature, Quantities,
and Units of Measure for the American Journal of Clinical Pathology: The Metric System
and Clinical Chemistry. Am J Clin Pathol
59:277-281, 1973
International Union of Pure and Applied Chemistry and International Federation of Clinical
Chemistry: Quantities and Units in Clinical
Chemistry. Information Bulletin No. 20. Oxford, IUPAC, 1972, pp 24
International Union of Pure and Applied Chemistry and International Federation of Clinical
Chemistry: List of Quantities in Clinical
Chemistry. Information Bulletin No. 21. Oxford, IUPAC, 1972, pp 24
IUPAC Division of Physical Chemistry, Commission on Symbols, Terminology, and Units:
Manual of Symbols and Terminology for
Physicochemical Quantities and Units. London,
Butterworths, 1970, pp 44 (Also in: Pure Appl
Chem 21:1-44, 1970)
National Physical Laboratory: SI. T h e International System of Units. London, Her Majesty's
Stationery Office, 1970, pp ix + 45
Leukocyte Alkaline Phosphatase in Agnogenic Myeloid Metaplasia
To the Editor:—Information on the leukocyte alkaline phosphatase score (LAP) in
agnogenic myeloid metaplasia is limited. 2 ' 3
At the Mayo Clinic from 1965 to 1970, LAP
was determined by the method of Kaplow 1
in 78 patients who had agnogenic myeloid
metaplasia. Forty-one patients had high
scores (more than 100), 20 patients had
normal scores (between 30 and 100), and 17
had low scores (below 30). No correlation
existed between LAP and hemoglobin concentration, leukocyte count, platelet count,
spleen size, or marrow status. Also, there
was no relationship between LAP and
leukemic transition or overall survivorship.
However, in a follow-up study of 7 years, a
significant negative correlation was found
(Key words: Alkaline phosphatase; Agnogenic
myeloid metaplasia; Leukocyte.)
between LAP and the absolute percentage
of immature cells in the peripheral blood.
MURRAY N. S I L V E R S T E I N ,
M.D.
Division of Hematology and Internal Medicine
L I L A R. ELVEBACK, P H . D .
Section of Medical Research Statistics
Mayo Clinic and Mayo Foundation
Rochester, Minnesota
References
1. Kaplow LS: Cytochemistry of leukocyte alkaline
phosphatase: Use of complex naphthol AS
phosphates in azo dye-coupling technics. Am J
Clin Pathol 39:439-449, 1963
2. Koler RD, Seaman AJ, Osgood EE, et al: Myeloproliferative diseases: Diagnostic value of the
leukocyte alkaline phosphatase test. Am J Clin
Pathol 30:295-301, 1958
3. Mitus WJ, Bergna LJ, Mednicoff IB, et al: Alkaline
phosphatase of mature neutrophils in chronic
forms of the myeloproliferative syndrome. Am
J Clin Pathol 30:285-294, 1958