HUMAN BIOLOGY

148 Chapter 8

What is the purpose of rh blood typing?

• In some people, red blood cells are marked with an Rh protein.
  If this Rh^1 blood mixes with the Rh– blood of someone else,
  the Rh^2 individual will develop antibodies against it. The
  antibodies will trigger an immune response against Rh^1 red
  blood cells if the person is exposed to them again.

taKe-Home message

Rh blood typing Chemical
test that determines whether
red blood cells bear an Rh
marker.

rh blood typing

Currently, a known Rh^2 woman can be treated after

her first pregnancy with an anti-Rh gamma globulin

(RhoGam) that will protect her next fetus. The drug will

inactivate Rh^1 fetal blood cells circulating in the mother’s

bloodstream before she can become sensitized and begin

producing anti-Rh antibodies. In non-maternity cases, an

Rh^2 person who receives a transfusion of Rh^1 blood also

can have a severe negative reaction if he or she has previ-

ously been exposed to the Rh marker.

there are also many other markers

on red blood cells

Besides the Rh and AB blood marker proteins, hundreds of

others are now known to exist. These markers are a bit like

needles in a haystack—they are widely scattered within

the human population and usually don’t cause problems

in transfusions. Reactions do occur, though, and except

in extreme emergencies, hospitals use a method called

cross-matching to exclude the possibility that blood to be

transfused and that of a patient might be incompatible due

to the presence of a rare blood cell marker outside the ABO

and Rh groups.

n Another surface marker on red blood cells that can cause

agglutination is the Rh factor, which was first identified in

the blood of rhesus monkeys.

rh blood typing looks for

an rh marker

Rh blood typing determines the

presence or absence of an Rh marker.

If your blood cells bear this marker,

you are Rh^1 (positive). If they don’t have the marker, you are

Rh^2 (negative). When a person’s blood type is determined,

the ABO blood type and Rh type are usually combined.

For instance, if your blood is type A and Rh negative, your

blood type will be given as type A^2.

Most people don’t have antibodies against the Rh

marker. But an Rh^2 person who receives a transfusion of

Rh^1 blood will make antibodies against the marker, and

these will continue circulating in the person’s bloodstream.

If an Rh^2 woman becomes pregnant by an Rh^1 man,

there is a chance the fetus will be Rh^1. During pregnancy

or childbirth, some of the fetal red blood cells may leak into

the mother’s bloodstream. If they do, her body will produce

antibodies against Rh (Figure 8.6). If she gets pregnant

again, Rh antibodies will enter the bloodstream of this new

fetus. If its blood is Rh^1 , its mother’s antibodies will cause

its red blood cells to swell and burst.

In extreme cases, called hemolytic disease of the

newborn, so many red blood cells are destroyed that the

fetus dies. If the condition is diagnosed before or during a

live birth, the baby can survive by having its blood replaced

with transfusions free of Rh antibodies.

Figure 8.6 Animated! In some cases antibodies develop in response to Rh^1 blood. A Blood cells from an Rh^1 fetus leak into the Rh^2

mother’s bloodstream. B The mother now develops antibodies against a subsequent Rh^1 fetus.

Rh+

markers

on the red

blood cells

of a fetus

fetus

Rh Rh

+–

anti-Rh+

antibody

molecules

any

subsequent

Rh+ fetus

AB

8.5

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