Transcript MLAB 1315- Hematology Fall 2007 Keri Brophy

MLAB 1315- Hematology
Fall 2007
Keri Brophy-Martinez
Unit 16: Extracorpuscular Defects
Immune Hemolytic Anemia

Mechanisms of Immune Hemolysis

Intravascular


Intravascular immune hemolysis occurs within the vascular
system and results from activation of the classic complement
pathway via immunoglobulin G (IgG) or IgM antibodies.
Antibodies bind to antigens on red cells and activate complement
resulting in lysis of the cell.
Extravascular

Antibody coated red cells are fully or partially phagocytized by
cells in the reticuloendothelial system (RES), particularly in the
spleen and liver. Partially phagocytized cells are seen as
spherocytes on the peripheral smear.
Laboratory findings




Peripheral smear - spherocytes
Serum bilirubin
Urine and stool urobilinogen
Positive direct antiglobulin test (DAT
Classification

Alloimmune Hemolytic Anemia

A foreign antigen stimulates the host’s immune
system to produce a corresponding antibody
called an alloantibody.
Types of Alloimmune Hemolytic
Anemia

Acute transfusion reaction


The wrong ABO type of blood is transfused. If a patient
develops symptoms such as fever, shaking, chills, pain or
burning at the site of the iv, the transfusion should be
stopped immediately.
Delayed transfusion reaction

Sensitization to non-ABO blood groups occurs during a
primary transfusion. When re-exposed during a second
transfusion, antibodies build up and a delayed reaction
occurs. Symptoms are usually mild and non-specific.
Types of Alloimmune Hemolytic
Anemia

Hemolytic Disease of the Newborn (HDN)

This is caused when the mother’s and baby’s blood groups are
incompatible and there is an exchange of fetal-maternal blood during
delivery. The mother builds antibodies against the fetal red cells
which then become coated with antibody and are destroyed in the
baby’s RES. This could be associated with ABO or Rh
incompatibility. It can be severe and treatment would consist of an
exchange transfusion of the newborn.
Classification

Autoimmune Hemolytic Anemia (AIHA)

Caused by an altered immune response resulting
in production of antibody against the patient’s
own red cells, with subsequent hemolysis.
Types of Autoimmune Hemolytic
Anemia

Warm AIHA


Cold agglutinins - non-pathologic


Almost all adults have cold antibodies in low quantity which cause no
problems because they react in the temperature range of 4̊ to 22̊ C. The
antibody is usually anti-I.
Cold Agglutination Syndrome – pathologic


IgG coats red cells with or without complement fixation
Caused by a cold autoantibody that reacts at or above 30̊ C. Seasonal
hemolytic anemia during the winter months. Usually not severe. RBC’s
agglutinate at room temperature and will be seen as clumps on a peripheral
smear. This can also be secondary to an infection, especially Mycoplasma
pneumoniae.
Paroxysmal Cold Hemoglobinurea

Caused by a cold-reacting IgG autoantibody. Can be severe. Treatment is to
avoid the cold.
Drug-Induced Immune Hemolytic
Anemia

Represents about 12% of immune hemolytic
anemias. Usually an IgM antibody and may
be cause by many drugs, some of which are
methyldopa (Aldomet), penicillin,
cephalosporins and streptomycins.
Nonimmune Hemolytic Anemia

These anemias represent a group of conditions
that lead to the shortened survival of red cells
by various mechanisms.
Mechanisms of nonimmune hemolytic
anemia

Intracellular infections

Malaria - this parasite carried by a mosquito lives in the
red cell at one of the stages in its life cycle and causes the
red cell to burst, releasing the parasite into the
bloodstream.. This is the most common infectious disease
in the world that causes a hemolytic anemia. Species of
malaria include:

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

Plasmodium vivax
P. faciparum - most fatal
P. malariae - uncommon
P. ovale - uncommon
Peripheral smear examination will reveal intracellular parasites.
Babesiosis - Tick-borne parasite
Mechanisms of nonimmune hemolytic
anemia

Extracellular infections


Bartonellosis
Clostridium perfringens (welchii) - causes
gangrene
Mechanical etiologies

Cardiac prothesis


March hemoglobinurea


Peripheral smear shows RBC fragments, helmet cells and occasional
spherocytes.
Caused by traumatic destruction of the red cells in strenuous and
sustained physical activity such as marching.
Microangiopathic hemolytic anemia

Caused by fragmentation of the red cells by fibrin strands as they pass
through abnormal arterioles. The fibrin strands are the results of
intravascular coagulation as seen in hemolytic uremic syndrome
(HUS) or thrombotic thrombocytopenia purpura (TTP). (To be
discussed in coagulation)
Mechanical etiologies con’t

Venoms


Some spiders contain enzymes that lyse the red
cell membrane. Snake venoms rarely cause lysis
in vivo.
Osmotic effects

Burns over more than 15% of the body can cause
hemolysis. It is thought that the direct effect of
the heat causes the red cells to fragment and
burst.