Autoimmune Hemolytic
Anemias
By ScholarRx
Updated March 10, 2021
access_time13 min
Learning Objectives (5)
After completing this brick, you will be able to:
● Describe the typical clinical course and treatment of autoimmune
hemolytic anemia.
● 1
● Describe and identify the morphologic changes present in the blood
in patients with warm and cold autoimmune hemolytic anemia.
● 2
● Describe the most important diagnostic test used to differentiate
autoimmune hemolytic anemia from other types of hemolytic
anemia.
● 3
● List and understand the characteristic complete blood count values in
autoimmune hemolytic anemia.
● 4
● Describe the pathogenesis of warm and cold autoimmune hemolytic
anemia (AHA), paying particular attention to the type of antibody
and site of hemolysis in each.
● 5
cableCASE CONNECTION
,VP is 28-year-old woman admitted to the hospital with fever, chills,
and cough. “I am having difficulty breathing. If I limit what I do, I’m
okay,” she says. “But no matter what, I am always tired.” On physical
examination, her temperature is 101.2°F, pulse 114/min, and blood
pressure 122/78 mm Hg. You hear rales in her right lower lobe and
order a chest x-ray, which confirms pneumonia. You begin treatment
but then look carefully at her admission labs as they trickle in: her
hemoglobin is low, reticulocyte count elevated, and total bilirubin high,
almost all indirect.
How will you characterize VP’s anemia? What treatment will you
recommend? Consider your answers as you read, and we’ll revisit at
the end of the brick.
GO TO CONCLUSION arrow_downward
What Are Autoimmune Hemolytic
Anemias?
Before we get into the details of our discussion, let’s pause and just
look at the name of this disorder: autoimmune hemolytic anemia. You
probably already know that “anemia” refers to a decrease in red cell
mass and that “hemolysis” refers to the destruction of red cells. And
you probably also know that “autoimmune” refers to some
mechanism by which the body is attacking itself. So even before we
get into our discussion, we’ve created a framework for understanding
this disorder: it is a disorder in which the body attacks and destroys its
own red blood cells (RBCs), leading to a decreased red blood cell
mass. Now let’s start building on that framework.
,The first thing to know about autoimmune hemolytic anemia (AHA)
is that there are two types: warm AHA and cold AHA. Warm and cold
refer to the temperature at which the patient’s anti-RBC antibodies are
most active. In warm AHA, the antibodies are most active at warm
temperatures (normal body temperature, actually), and in cold AHA,
the antibodies are most active at—you guessed it—cooler
temperatures.
It might seem silly and pointless to distinguish between warm- and
cold-reacting antibodies, but actually, it is very relevant from a
clinical perspective. Warm-reacting antibodies quickly attach to RBCs
and mark them for destruction. Cold-reacting antibodies only attach to
RBCs in peripheral parts of the body, particularly when the ambient
temperature is cool; they fall off the RBCs as blood circulates through
central regions of the body, where the temperature is warmer.
That’s the basis for dividing these anemias into two groups. There is
more to these anemias than temperature, of course—so let’s move
ahead in our discussion, starting with warm AHA.
Warm Autoimmune Hemolytic
Anemias
In warm AHA, antibodies attach to RBCs in areas where the blood is
warm, in the central aspects of the body, rather than the periphery.
More specifically, these antibodies are most reactive at 37°C. Warm
AHA characteristically has immunoglobulin G (IgG) antibodies that
recognize a host’s own RBC antigens (Figure 1). As the IgG-coated
RBCs travel through the vasculature, they will eventually reach the
spleen. There, the RBCs are trapped by splenic macrophages (which
recognize the Fc portion of antibodies), which then leads to
phagocytosis and hemolysis. Because the hemolysis occurs in the
, spleen, rather than blood vessels, warm AHAs are characterized by
extravascular hemolysis.
Figure 1
Complete phagocytosis does not always occur. Often a macrophage
recognizes the IgG and takes a partial bite out of the RBC, resulting in
the classic RBC biconcave disk structure becoming a spherocyte (see
laboratory diagnosis below). As the newly formed spherocytes
Anemias
By ScholarRx
Updated March 10, 2021
access_time13 min
Learning Objectives (5)
After completing this brick, you will be able to:
● Describe the typical clinical course and treatment of autoimmune
hemolytic anemia.
● 1
● Describe and identify the morphologic changes present in the blood
in patients with warm and cold autoimmune hemolytic anemia.
● 2
● Describe the most important diagnostic test used to differentiate
autoimmune hemolytic anemia from other types of hemolytic
anemia.
● 3
● List and understand the characteristic complete blood count values in
autoimmune hemolytic anemia.
● 4
● Describe the pathogenesis of warm and cold autoimmune hemolytic
anemia (AHA), paying particular attention to the type of antibody
and site of hemolysis in each.
● 5
cableCASE CONNECTION
,VP is 28-year-old woman admitted to the hospital with fever, chills,
and cough. “I am having difficulty breathing. If I limit what I do, I’m
okay,” she says. “But no matter what, I am always tired.” On physical
examination, her temperature is 101.2°F, pulse 114/min, and blood
pressure 122/78 mm Hg. You hear rales in her right lower lobe and
order a chest x-ray, which confirms pneumonia. You begin treatment
but then look carefully at her admission labs as they trickle in: her
hemoglobin is low, reticulocyte count elevated, and total bilirubin high,
almost all indirect.
How will you characterize VP’s anemia? What treatment will you
recommend? Consider your answers as you read, and we’ll revisit at
the end of the brick.
GO TO CONCLUSION arrow_downward
What Are Autoimmune Hemolytic
Anemias?
Before we get into the details of our discussion, let’s pause and just
look at the name of this disorder: autoimmune hemolytic anemia. You
probably already know that “anemia” refers to a decrease in red cell
mass and that “hemolysis” refers to the destruction of red cells. And
you probably also know that “autoimmune” refers to some
mechanism by which the body is attacking itself. So even before we
get into our discussion, we’ve created a framework for understanding
this disorder: it is a disorder in which the body attacks and destroys its
own red blood cells (RBCs), leading to a decreased red blood cell
mass. Now let’s start building on that framework.
,The first thing to know about autoimmune hemolytic anemia (AHA)
is that there are two types: warm AHA and cold AHA. Warm and cold
refer to the temperature at which the patient’s anti-RBC antibodies are
most active. In warm AHA, the antibodies are most active at warm
temperatures (normal body temperature, actually), and in cold AHA,
the antibodies are most active at—you guessed it—cooler
temperatures.
It might seem silly and pointless to distinguish between warm- and
cold-reacting antibodies, but actually, it is very relevant from a
clinical perspective. Warm-reacting antibodies quickly attach to RBCs
and mark them for destruction. Cold-reacting antibodies only attach to
RBCs in peripheral parts of the body, particularly when the ambient
temperature is cool; they fall off the RBCs as blood circulates through
central regions of the body, where the temperature is warmer.
That’s the basis for dividing these anemias into two groups. There is
more to these anemias than temperature, of course—so let’s move
ahead in our discussion, starting with warm AHA.
Warm Autoimmune Hemolytic
Anemias
In warm AHA, antibodies attach to RBCs in areas where the blood is
warm, in the central aspects of the body, rather than the periphery.
More specifically, these antibodies are most reactive at 37°C. Warm
AHA characteristically has immunoglobulin G (IgG) antibodies that
recognize a host’s own RBC antigens (Figure 1). As the IgG-coated
RBCs travel through the vasculature, they will eventually reach the
spleen. There, the RBCs are trapped by splenic macrophages (which
recognize the Fc portion of antibodies), which then leads to
phagocytosis and hemolysis. Because the hemolysis occurs in the
, spleen, rather than blood vessels, warm AHAs are characterized by
extravascular hemolysis.
Figure 1
Complete phagocytosis does not always occur. Often a macrophage
recognizes the IgG and takes a partial bite out of the RBC, resulting in
the classic RBC biconcave disk structure becoming a spherocyte (see
laboratory diagnosis below). As the newly formed spherocytes
