CLIN. CHEM. 20/5, 615-616
(1974)
Specific Gravity of Blood and Plasma at 4 and 37 #{176}C
Raymond J. Trudnowski and Rodolfo C. Rico
The specific
gravity
(relative
density)
of human
whole blood and plasma from 25 healthy volunteers
was determined
gravimetrically.
For whole blood it
was found to be 1.0621 (95% confidence
interval:
1.0652-1.0590)
at 4 #{176}C
and 1.0506 (95% confidence
interval: 1.0537-1.0475)
at 37 #{176}C.
Plasma specific
gravity
was
1.0310
(95% confidence
interval:
1.0324-1.0296)
at 4 #{176}C
and 1.0205 (95% confidence
interval: 1.0216-1.0193)
at 37 #{176}C.
All of these values
are referred to the density of water at 4 #{176}C.
We
show the relationship
between these values and
those given in the literature for measurements at 25
#{176}C.
There was a small increase in whole blood specific gravity with increasing hematocrit, but it was
not statistically significant over the 40-56 hematocrit
range studied.
The
specific
gravity
(relative
density)
of whole
blood
and plasma has been used to estimate its hemoglobin
(1)
and protein (2) content. Improved techniques
for directly
determining
these values have relegated
specific
gravity
to use in blood banks
determinations
for screening
of
pur-
poses.
In sensitive
clinical
knowledge of the correct
blood and plasma
error
in these
errors deriving
levels, uneven
chemical
value
and enzymatic
for the specific
can be very useful.
determinations
A major
is in volume
analyses,
gravity of
source of
measurement,
from (e.g.) improper alignment
of liquid
drainage of liquid from pipet walls, and
temperature
variations
imetry of samples
and
during
reagents
pipetting.
Because
grayis not subject
to errors of
this kind, its use should improve the accuracy of such determinations.
Weight can be expressed as volume if the
specific gravity or density is known.
The specific
gravity
of blood or plasma
is usually
reported
at 20 or 25 #{176}C,
which is considered
to be “room
temperature.”
Room temperature,
however,
varies considerably. Temperatures
of 4 or 37 #{176}C
are more meaningful,
because these temperatures
are commonly
maintained
in
laboratory equipment.
Data on the specific gravity of human
at these temperatures
were unavailable,
blood and plasma
so we determined
these
report
values
for our laboratory
use,
and
them
here
for others who may find them useful.
Department
of Anesthesiology,
tute, New York State Department
lo, N. Y. 14203.
Received Jan. 28, 1974; accepted
Roswell Park Memorial Instiof Health, 666 Elm St., BuffaFeb. 25, 1974.
Materials and Methods
We used 2-ml volumetric
flasks that had been calibrated at 37 and 4 #{176}C
by weighing
chemically
pure mercury
in
them. The subjects
contributing
blood were 25 members
of the Institute
and laboratory
staff (six women and 19
men) who were in apparent
good health.
Their ages
ranged between 29 and 58 years. Sampling was done between 9:30 a.m. and 11:00a.m., before lunch was eaten.
From
the antecubital
vein,
we obtained
10 ml of blood,
which
was promptly heparinized.
The blood and closed
volumetric
flasks were cooled to 4 #{176}C
for 1 h. The volumetric flask was then filled with blood to the calibration
mark, stoppered,
warmed
to room temperature,
and
weighed without
the stopper.
It was then warmed
to 37 #{176}C
and reweighed
after excess blood above the calibration
line was removed.
The procedure
was repeated
with plasma. All measurements
were made in duplicate.
Microhematocrits
were determined
in duplicate
in capillary
tubes
after centrifuging
for 5 mm at 7000 x g.
Results
Microhematocrit
values
varied
between
40
and
56
(mean,
48.1). The mean specific
gravity
of whole blood
was 1.0581 at 37 #{176}C
(water reference, 37 #{176}C)
with a 95%
confidence interval of 1.0612-1.0550. It was 1.0621 at 4 #{176}C
(water reference, 4 #{176}C)
with a 95% confidence
interval of
1.0652-1.0590.
Mean
plasma
specific
gravity,
use of the water reference
again
temperatures
measured
mentioned
with
the
above,
was
1.0278 at 37 #{176}C
(95% confidence
interval:
1.0290and 1.0310 at 4 #{176}C
(95% confidence
interval:
1.0324-1.0296).
Converting
the values measured
at 37 #{176}C
to a reference
value of the density of water at 4 #{176}C
gave the following
values:
whole
blood,
1.0506 (95% confidence
interval:
1.0537-1.0475)
and plasma,
1.0205 (95% confidence
interval: 1.0216-1.0193).
The values referred
to water at 4 #{176}C
are plotted
in Figure
1, together
with standard
values
given in the literature
at 25 #{176}C
(3).
1.0266)
Discussion
The
usual
methods
of determining
the
specific
gravity
of blood involve comparison
with a solution of known specific gravity
(1, 2, 4-8). Although
these are useful and
simple, we thought
that volumetric
errors might be introduced if we used them here. We therefore
returned
to the
fundamental
method
of weighing
an accurately
measured
volume
in a volumetric
CLINICAL
flask and comparing
CHEMISTRY,
its mass with
Vol. 20, No. 5, 1974
615
1.0700
I.080
1.070
.0600
>-
I-
T
>
4
0
I 0500
.060
4’
UU
UJ
a.
+
.050
.0400
>
.040
.0300
0
40-45
45.1-50
50.1-56
HEMATOCRI T
Fig. 2. Relation of whole blood specific
tocrit
.0200
gravity
to hema-
hematocrit.
Ordinate,
specific gravity. S. mean specific gravity
at 37 #{176}C,
referred to water at 37 #{176}C;
0, mean specific gravity at 4 #{176}C
referred to water at 4 #{176}C
Abscissa,
1.0100 0
10
20
30
40
TEMPERATURE-DEGREESCENTIGRADE
Fig. 1. Specific
healthy adults
gravity
whole
of
blood
and
plasma-
Abscissa: temperature #{176}C.
Ordinate: specific gravity referred to water at
4 #{176}C.
#{149},
whole blood; 0 plasma
the mass of an equal volume
dard.
There
is a linear
the reference
gravity
values
of water
relationship
taken
between
our
given for 25 #{176}C
(Figure
as the stanvalues
and
1). Specific
declined
with temperature
as expected.
We have
this Figure to obtain specific gravities
graphiat other commonly
used temperatures,
such as 30
been using
cally
#{176}C.
We find the value for 4 #{176}C
is useful in another
way. If a
blood specimen
is stored
refrigerated
until analysis,
the
collecting
tubes,
with or without
reagent,
can also be
preweighed
and stored.
When blood is added,
the tube
may be reweighed
at a convenient
volume accurately
calculated.
One would expect the specific
time
gravity
and the sample
of blood
not only
to decrease with temperature
but also to increase with the
hematocrit.
For our subjects, there was an insignificant
specific gravity increase with increasing hematocrit
(Figure 2). The slope of the average reading at both temperatures was 0.0011. In this hematocrit
range, it is doubtful
whether
one
would
be justified
values for specific gravity
Compensating
manipulations
616
CLINICAL
CHEMISTRY,
in using
different
mean
for the various hematocrits.
such as standardizing
plas-
Vol. 20, No.5.1974
ma content
and adjusting
pH and Pc02 by tonometry
would negate any benefits.
Mrs. Okee Jung,
the hematocrit
to a reference
might
introduce
errors that
M. S., Department
of Biostatistics,
statisti-
cally analyzed the data.
References
1. Van Slyke, D. D., Phillips,
al.,
Calculation
of hemoglobin
R., Hamilton,
from
P. B., Dole, V. P., et
blood specific gravities. J.
Biol. Chem. 183,349(1950).
2. Kagan, B. M., A simple method for the estimation
of total
protein
content of plasma and serum. II The estimation of total
protein content of human plasma and serum by the use of the
falling drop method. J. Clin. Invest. 17, 373 (1938).
3. Handbook of Biological Data. William S. Spector. Ed. National Academy of Sciences. National Research Council. Washington
D.C., 1956,p51.
4. Roy, C. S., Note on a method of measuring the specific gravity
of the blood for clinical use. Edinburgh
Clin. Pathol. J. 1, 561
(1883-1884).
5. Hammerschlag,
A., Eine neue Methode zur Bestimmung
des
specifischen Gewichts des Blutes. Z. KIm. Med. 20,444(1892).
6. Reznikoff, P., A mathod for the determination
of the specific
gravity of blood cells. J. Exp. Med. 38, 441 (1923).
7. Barbour, A. G., and Hamilton, W. F., The falling drop method
for determining specific gravity. J. Biol. Chem. 69, 625 (1926).
8. Poller, L., An evaluation of the copper sulphate blood specific
gravity method with reference to the control of fluid therapy in
mass casualties. Acta Haematol. 21, 242 (1959).