Chapter 17
Blood
653
17
Check Your Understanding
12.
Nigel is told he has type B blood. Which ABO antibodies
does he have in his plasma? Which agglutinogens are on his
RBCs? Could he donate blood to an AB recipient? Could he
receive blood from an AB donor? Explain.
For answers, see Appendix H.
Diagnostic Blood Tests
Explain the diagnostic importance of blood testing.
A laboratory examination of blood yields information that can
be used to evaluate a person’s health. For example, in some
anemias, the blood is pale and has a low hematocrit. A high
fat content (
lipidemia
) gives blood plasma a yellowish hue and
forecasts problems in those with heart disease. Blood glucose
tests indicate how well a diabetic is controlling diet and blood
sugar levels. Leukocytosis signals infections; severe infections
yield larger-than-normal buffy coats in the hematocrit.
Microscopic studies of blood can reveal variations in the size
and shape of erythrocytes that indicate iron deficiency or per-
nicious anemia. A
differential white blood cell count
, which
Transfusion reactions can also cause fever, chills, low blood
pressure, rapid heartbeat, nausea, vomiting, and general toxicity,
but in the absence of renal shutdown, these reactions are rarely
lethal. Treatment of transfusion reactions focuses on preventing
kidney damage by administering fluid and diuretics to increase
urine output, diluting and washing out the hemoglobin.
As indicated in Table 17.4, group O red blood cells bear nei-
ther the A nor the B antigen, so theoretically group O is the
universal donor
. Indeed, some laboratories are developing
methods to enzymatically convert other blood types to type
O by clipping off the extra (A- or B-specific) sugar molecule.
Since group AB plasma is devoid of antibodies to both A and
B antigens, group AB people are theoretically
universal recipi-
ents
and can receive blood transfusions from any of the ABO
groups. However, these classifications are misleading, because
they do not take into account the other agglutinogens in blood
that can trigger transfusion reactions.
±e risk of transfusion reactions and transmission of life-
threatening infections (particularly with HIV) from pooled
blood transfusions has increased public interest in
autologous
transfusions
(
auto
5
self). In autologous transfusions, the pa-
tient
predonates
his or her own blood, and it is stored and im-
mediately available if needed during an operation.
Blood Typing
It is crucial to determine the blood group of both the donor and
the recipient
before
blood is transfused.
Figure 17.16
briefly
outlines the general procedure for determining ABO blood
type. Because it is so critical that blood groups be compatible,
cross matching is also done.
Cross matching
tests whether the
recipient’s serum will agglutinate the donor’s RBCs or the do-
nor’s serum will agglutinate the recipient’s RBCs. Typing for Rh
factors is done in the same manner as ABO blood typing.
Restoring Blood Volume
When a patient’s blood volume is so low that death from shock is im-
minent, there may not be time to type blood, or appropriate whole
blood may be unavailable. Such emergencies demand that blood
volume
be replaced immediately to restore adequate circulation.
Fundamentally, blood consists of proteins and cells sus-
pended in a salt solution. Replacing lost blood volume essen-
tially consists of replacing that isotonic salt solution.
Normal
saline
or a
multiple electrolyte solution
that mimics the electro-
lyte composition of plasma (for example,
Ringer’s solution
) are
the preferred choices.
You might think that it would be important to add materi-
als to mimic the osmotic properties of albumin in blood, and
indeed this has been widely practiced. However, studies have
shown that
plasma expanders
such as
purified human serum
albumin, hetastarch
, and
dextran
provide no benefits over much
cheaper electrolyte solutions and are actually associated with
significant complications of their own. Volume replacement re-
stores adequate circulation but cannot, of course, replace the
oxygen-carrying capacity of the lost red blood cells. Research
on ways to replace that capability by using artificial blood sub-
stitutes is ongoing.
Serum
Anti-A
RBCs
Anti-B
Type AB
(contains
agglutinogens A and B;
agglutinates with both
sera)
Blood being tested
Type A
(contains
agglutinogen A;
agglutinates with anti-A)
Type B
(contains
agglutinogen B;
agglutinates with anti-B)
Type O
(contains no
agglutinogens; does not
agglutinate with either
serum)
Figure 17.16
Blood typing of ABO blood types.
When serum
containing anti-A or anti-B agglutinins is added to a blood sample
diluted with saline, agglutination will occur between the agglutinin
and the corresponding agglutinogen (A or B).
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