Brief Summary of Acquired Hemolytic Anemias

1. Acquired Haemolytic Anaemia
MARWA AHMED GAMALELDIN

2. Causes of Acquired hemolytic anemias
a. Mechanical
(1) Macroangiopathic (march hemoglobinuria, artificial heart valves)
(2) Microangiopathic (disseminated intravascular coagulation, DIC; thrombotic
thrombocytopenic purpura, TTP; vasculitis)
(3) Parasites and microorganisms (malaria, bartonellosis, babesiosis, Clostridium welchii, etc.)
b. Antibody-mediated
(1) Warm-type autoimmune hemolytic anemia
(2) Cryopathic syndromes (cold agglutinin disease, paroxysmal cold hemoglobinuria,
cryoglobulinemia)
(3) Transfusion reactions (immediate and delayed)
c. Hypersplenism
d. Red cell membrane disorders
(1) Spur cell hemolysis
(2) Acquired acanthocytosis and acquired stomatocytosis, etc.
e. Chemical injury and complex chemicals (arsenic, copper, chlorate, spider, scorpion, and
snake venoms, etc.)
f. Physical injury (heat, oxygen, radiation)
G. PNH

3. Classification of AIHA
Immune
• Autoimmune
– Warm Ab type
– Cold Ab type
• Alloimmune
– Hemolytic transfusion reactions
– Hemolytic disease of the newborn
– Allografts, especially marrow transplantation
• Drug associated

4. Hemolytic Anemia Resulting from
Immune Injury
• Autoimmune HA is characterized by 2 main
features:
1. shortened RBC survival and
2. presence of autoAbs directed against autologous
RBCs.
• A positive direct antiglobulin test (DAT, also known
as the Coombs test) is essential for diagnosis.

5. • Most patients with AHA (80%) exhibit warm-
reactive antibodies of the IgG isotype.
• Most of the remainder of patients exhibit cold-
reactive autoAbs. Two types of cold-reactive
autoAbs to RBCs are recognized:
Cold agglutinins (IgM)
Cold hemolysins (IgG)

6. • About half of patients with AHA have no underlying
associated disease (primary).

7. Classification of Hemolytic Anemia as a Result of
Immune Injury
I. Warm-autoantibody type:
autoAb maximally active at body temperature (37°C).
A. Primary or idiopathic warm AHA
B. Secondary warm AHA
1. Associated with lymphoproliferative disorders (e.g., HD, lymphoma)
2. Associated with the rheumatic disorders, particularly SLE
3. Associated with certain nonlymphoid neoplasms (e.g., ovarian
tumors)
4. Associated with certain chronic inflammatory diseases (e.g.,
ulcerative colitis)
5. Associated with ingestion of certain drugs (e.g., -methyldopa)

8. II. Cold-autoantibody type:
autoantibody optimally active at temperatures <37°C .
A. Mediated by cold agglutinins
1. Idiopathic (primary) chronic cold agglutinin disease
2. Secondary cold agglutinin hemolytic anemia
a. Postinfectious (e.g., Mycoplasma pneumoniae or infectious
mononucleosis)
b. Associated with malignant B cell lymphoproliferative disorder
B. Mediated by cold hemolysins
1. Idiopathic (primary) paroxysmal cold hemoglobinuria (very rare)
2. Secondary
a. Donath-Landsteiner hemolytic anemia, usually associated with an acute
viral syndrome in children (relatively common)
b. Congenital or tertiary syphilis in adults (very rare)

9. III. Mixed cold and warm autoantibodies
A. Primary or idiopathic mixed AHA
B. Secondary mixed AHA
1. Associated with the rheumatic disorders, particularly SLE
IV. Drug-immune hemolytic anemia
A. Hapten or drug adsorption mechanism
B. Ternary (immune) complex mechanism
C. True autoantibody mechanism

10. Warm-antibody AHA
Epidemiology
• The frequency of primary warm-antibody AHA is 50%
of all cases.
• Careful follow up of patients with primary AHA is
essential,
– because hemolytic anemia may be the presenting finding
in a patient who subsequently develops overt evidence of
an underlying disorder.
• Warm-antibody AHA has been diagnosed in people of
all ages, from infants to the elderly. The majority of
patients are older than 40 years.

11. Etiology
• The etiology of AHA is unknown.
• In warm-antibody AHA, the autoantibodies that
mediate RBC destruction are predominantly IgG
with high binding affinity for RBCs at 37°C.
• As a result, the major share of plasma autoantibody
is bound to the patient's circulating RBCs.

12. • Normal subjects sometimes have a positive DAT
when they volunteer to donate blood (one in
10,000).
• The positive DAT in these normal donors often
results from warm-reacting IgG autoAbs.
• Although many of these donors remain Coombs
positive without developing overt hemolytic
anemia, a few have been documented to
develop AHA.

13. Pathogenesis
• In warm-antibody AHA, the patient's RBCs typically
are coated with IgG autoAbs with or without
complement proteins.
• autoAb-coated RBCs are trapped by macrophages in
the spleen and, to a lesser extent, by Kupffer cells in
the liver.
• The process leads to generation of spherocytes and
fragmentation and ingestion of antibody-coated
RBCs.

14. • The macrophage has surface receptors for
– the Fc region of IgG and
– opsonic fragments of C3 (C3b and C3bi) and C4b.
• When present together on the RBC surface, IgG
and C3b/C3bi appear to act cooperatively as
opsonins to enhance trapping and phagocytosis.

15. Interaction of a trapped RBC with splenic macrophages
may result in:
1. Phagocytosis of the entire cell.
2. More commonly, a type of partial phagocytosis results
in spherocyte formation.
– portions of RBC membrane are internalized by the
macrophage. Because membrane is lost in excess of
contents, the noningested portion of the RBC assumes a
spherical shape.
– Spherical RBCs are more rigid than normal RBCs and are
fragmented further and destroyed in the spleen.

16. • Spherocytosis is a consistent and diagnostically
important hallmark of AHA,
• and the degree of spherocytosis correlates well with
the severity of hemolysis.

17. Immune hemolytic anemia

18. autoimmune haemolytic anaemia showing spherocytes
and polychromatic macrocytes

19. • Direct complement-mediated hemolysis with
hemoglobinuria is unusual in warm-antibody AHA.
• GPI-linked erythrocyte membrane proteins, such as
DAF(CD55) and HRF (CD59), may limit the action of
autologous complement on autoAb-coated RBCs.

20. • DAF inhibits the formation and function of
cell-bound C3-converting enzyme, thus
indirectly limiting formation of C5-converting
enzyme.
• HRF, on the other hand, impedes C9 binding
and formation of the C5b–9 membrane attack
complex.

21. Autoimmune hemolytic anemia: Warm antibody type (WAIHA)
Reaction at normal temperature (37 C)
= Antibody usually IgG type
= Antigenic determinant
Cell membrane
modified
Cell becomes
microspherocytes
With consequences similar to
hereditary spherocytosis-
early sequestration in spleen (RE)

22. Clinical Features of warm AHA
• Presenting: Usually anemia, occasionally jaundice.
• Symptom onset usually is slow and insidious, but
occasionally sudden onset of severe anemia and jaundice.
• In secondary AHA, the symptoms and signs of the
underlying disease may overshadow the hemolytic anemia.
• In idiopathic AHA, physical examination may be normal or
only modest splenomegaly.
• However, in very severe cases, patients may present with
fever, pallor, jaundice, hepatosplenomegaly, hyperpnea,
tachycardia, angina, or heart failure.

23. Laboratory Features
General Features
i. By definition, patients with AHA present with
anemia,
the severity of which ranges from life threatening to
very mild.

24. • Patients with warm-antibody AHA may present with:
hematocrit levels less than 10 percent or
compensated hemolytic anemia and a near-normal
hematocrit.
• For the latter patients, the predominant laboratory
features are:
1. an increased reticulocyte count and
2. a positive DAT.

25. ii. Platelet counts typically are normal.
Rarely, severe immune thrombocytopenia is
associated with warm-antibody AHA. This is
termed Evans syndrome.

26. Cold agglutinin disease
Epidemiology
• Cold agglutinin disease is less common than
warm-antibody AHA, only 10 to 20 % of all
cases of AHA.
• Paroxysmal cold hemoglobinuria constitutes 2
to 5 % of all cases of AHA.

27. Overview
• Cryopathic hemolytic syndromes are caused
by autoantibodies that bind RBCs optimally at
temperatures less than 37°C and usually less
than 31°C.

28. • Two major types of "cold antibody" may produce
AHA:
1. Cold agglutinins mediate cold agglutinin disease.
2. The Donath-Landsteiner autoAb, which is not an
agglutinin but a potent hemolysin, mediates
paroxysmal cold hemoglobinuria.

29. • In both cryopathic syndromes, the complement
system plays a major role in RBC injury;
• however, much greater potential exists for direct
intravascular hemolysis than in warm-antibody–
mediated AHA.

30. i. Cold agglutinin disease: chronic AHA in which the
autoantibody directly agglutinates human RBCs at
temperatures below body temperature, maximally
at 0 to 5°C.
• Cold agglutinins typically are IgM, although
occasionally may be other Igs.

31. ii. The Donath-Landsteiner antibody is responsible
for complement-mediated hemolysis in:
PCH, a very rare form of AHA in adults. The
disorder is characterized by recurrent episodes of
massive hemolysis following cold exposure.
more commonly in children as an acute, self-
limited single postviral episode hemolytic process.
– Thus, rather than PCH, a proposed term for this latter
entity is Donath-Landsteiner hemolytic anemia

32. Pathogenesis
• Most cold agglutinins are unable to agglutinate
RBCs at temperatures higher than 30°C.
• The highest temperature at which these antibodies
cause detectable agglutination is termed the
thermal amplitude.
• The value varies considerably among patients.
• Generally, patients with cold agglutinins with higher
thermal amplitudes have a greater risk for cold
agglutinin disease.

33. • The pathogenicity of a cold agglutinin depends upon
its ability to bind host RBCs and to activate
complement. This process is called complement
fixation.
• Although in vitro agglutination of the RBCs may be
maximal at 0 to 5°C, complement fixation by these
antibodies may occur optimally at 20 to 25°C and may
be significant at even higher physiologic temperatures.
• Agglutination is not required for the process.

34. • Cold agglutinins may bind to RBCs in superficial
vessels of the extremities, where the temperature
generally ranges between 28 and 31°C.
• Cold agglutinins of high thermal amplitude may
cause RBCs to aggregate at this temperature,
thereby impeding RBC flow and producing
acrocyanosis.
• In addition, the RBC-bound cold agglutinin may
activate complement via the classic pathway.

35. • Once activated complement proteins are deposited onto the RBC
surface,
 the cold agglutinin must remain bound to the RBCs for hemolysis to
occur.
 Instead, the cold agglutinin may dissociate from the RBCs at the higher
temperatures in the body core and again be capable of binding other
RBCs at the lower temperatures in the superficial vessels.
• As a result,
 patients with cold agglutinins of high thermal amplitude tend toward a
sustained hemolytic process and acrocyanosis.
 In contrast, patients with antibodies of lower thermal amplitude require
significant chilling to initiate complement-mediated injury of RBCs.

36. • This sequence may result in a burst of hemolysis
with hemoglobinuria.
• Cold agglutinins of the IgA isotype, an isotype that
does not fix complement, may cause acrocyanosis
but not hemolysis.

37. Autoimmune hemolytic anemia : Cold antibody type
Reaction at temperatures usually below 30 C
they occur in peripheral circulation and in cold weather.
Antibody
combines
with RBC
Reactions
= Antigenic determinant
Agglutination
Clinically present as painful
hand and feet
Amboceptor effect
Ag/Ab activates complement
Acute intravascular hemolysis
usually of IgM type

38. • Complement fixation by cold agglutinins may effect
RBC injury by two major mechanisms:
(1) direct lysis and
(2) opsonization for hepatic and splenic macrophages.

39. 1. Direct lysis requires propagation of the full C1-
to-C9 sequence on the RBC membrane leading
to intravascular hemolysis with hemoglobinemia
and hemoglobinuria.
• Intravascular hemolysis of this severity is
relativey rare because GPI-linked RBC membrane
proteins (DAF and HRF) protect against injury by
autologous complement components.

40. 2. Thus, the complement sequence on many RBCs is
completed only through the early steps, leaving opsonic
fragments of C3 (C3b/C3bi) and C4 (C4b) on the cell
surface.
• Activated macrophages may ingest C3b-coated particles
avidly.
• Accordingly, RBCs heavily coated with C3b (and/or C3bi)
may be removed from the circulation by macrophages
either in the liver or, to a lesser extent, the spleen.
• The trapped RBCs may be ingested entirely or released
back into the circulation as spherocytes after losing
plasma membrane.

41. Clinical features
• Most patients with cold agglutinin hemolytic anemia
have chronic hemolytic anemia with or without
jaundice. In other patients, the principal feature is
episodic, acute hemolysis with hemoglobinuria
induced by chilling.
• Acrocyanosis and other cold-mediated vasoocclusive
phenomena affecting the fingers, toes, nose, and ears
are associated with sludging of RBCs in the cutaneous
microvasculature.
• The hemolysis is self-limited, lasting 1 to 3 weeks
• Splenomegaly, a characteristic finding in
lymphoproliferative diseases or infectious
mononucleosis, may be observed in idiopathic cold
agglutinin disease.

42. • In paroxysmal cold hemoglobinuria, constitutional
symptoms are prominent during a paroxysm.
• A few minutes to several hours after cold exposure, the
patient develops aching pains in the back or legs,
abdominal cramps, and perhaps headaches.
• Chills and fever usually follow.
• The first urine passed after onset of symptoms typically
contains hemoglobin.
• The constitutional symptoms and hemoglobinuria
generally last a few hours.
• Raynaud phenomenon and cold urticaria sometimes
occur during an attack; jaundice may follow.

43. The blood film in acute paroxysmal cold
haemoglobinuria showing spherocytosis and
red cell agglutination.

44. Cold agglutinins
• Antibody not detected by the DAT because
they are readily dissociated from the RBCs
• Complement components however are more
securely bound
• Majority of cold agglutinins are anti I/i

45. • Cold agglutinins are distinguished by their ability to
directly agglutinate saline-suspended human RBCs at
low temperature, maximally at 0 to 5°C. The reaction is
reversible by warming.
• The DAT result is positive with anticomplement
reagents. The antibody itself, however, is not detected
by the DAT because the cold agglutinins readily
dissociate from the RBCs both in vivo and during the
washing steps of the standard antiglobulin procedure.

46. Drug mediated immune injury
• Major Mechanisms of Drug-Related Hemolytic
Anemia and Positive Direct Antiglobulin Tests:
1. Three mechanisms of drug-mediated
immune injury to RBCs.
2. Mediate protein adsorption to RBCs by
nonimmune mechanisms, but RBC injury
does not occur.

47. Drug-induced immune haemolytic
anaemias
Drugs may cause immlme haemolytic anaemias via three mechanisms:
1. Antibody directed against a drug-red cell membrane complex (e.g.
penicillin, ampicillin);
2. Deposition of complement via a drug-protein (antigen)-antibody
complex onto the red cell surface (e.g. quinidine, rifampicin); or
3. A true autoimmune haemolytic anaemia in which the role of the
drug is unclear (e.g. methyldopa).
In each case, the haemolytic anaemia gradually disappears when the
drug is discontinued but with methyldopa the autoantibody may
persist for several months.

48. Nonimmunologic Protein
Adsorption
Autoantibody Binding
Ternary Complex
Formation(Drug–
Antibody–Target Cell
Interaction)
Hapten/Drug Adsorption
Cephalothin
-Methyldopa
Quinidine
Penicillin
Prototype drug
Possibly alters red cell
membrane
Induces formation of
antibody to native red
cell antigen
Forms ternary complex
with antibody and red
cell membrane
component
Binds to red cell
membrane
Role of drug
Absent
Absent
Present
Present
Antibody to
drug

50. • Significantly, not all patients receiving high-
dose penicillin develop a positive DAT reaction
or hemolytic anemia because only a small
proportion of such individuals produce the
requisite antibody.

51. Clinical features
• A careful history of drug exposure should be
obtained from all patients with hemolytic
anemia and/or a positive DAT.
• As in idiopathic AHA, the clinical picture in
drug-immune hemolytic anemia is quite
variable. The severity of symptoms largely
depends upon the rate of hemolysis.

52. Laboratory features of IHA
• General features
I. Blood film:
1. Polychromasia indicates a reticulocytosis.
2. Spherocytes are seen in patients with moderate to severe
hemolytic anemia. Hereditary spherocytosis should be
excluded.
3. RBC fragments, nucleated RBCs, and occasionally
erythrophagocytosis by monocytes may be seen in severe
cases.
4. Most patients have mild leukocytosis and neutrophilia.
5. Patients with cold-antibody AHA may exhibit RBC
autoagglutination in the blood film and in chilled
anticoagulated blood.

54. II. The reticulocyte count usually is elevated.
• Nevertheless, early in the course of the disease,
more than one third of all patients may have
transient reticulocytopenia despite a normal or
hyperplastic erythroid marrow. The mechanism is
unknown

55. III. Marrow examination:
1. erythroid hyperplasia and
2. may provide evidence of an underlying
lymphoproliferative disorder.

56. IV. Hyperbilirubinemia (chiefly unconjugated) is
highly suggestive of hemolytic anemia,
although its absence does not exclude the
diagnosis.

57. V. Urinary urobilinogen is increased regularly, but bile is
not detected in the urine unless serum conjugated
bilirubin is increased.
VI. Usually, serum haptoglobin levels are low, and LDH
levels are elevated.
VII. Hemoglobinuria is encountered in
– rare patients with warm-antibody AHA and hyperacute
hemolysis,
– more commonly in patients with cold agglutinin disease,
and characteristically in patients with PCH
– with drug-immune hemolytic anemia mediated by the
ternary complex mechanism.

58. VIII.Direct Antiglobulin Test Pattern
Diagnosis of AHA or drug-immune hemolytic
anemia requires demonstration of
immunoglobulin and/or complement bound
to the patient's RBCs.

59. Schematic representation of the DAT

61. • Three possible major patterns of direct
antiglobulin reaction in AHA and drug-immune
hemolytic anemia exist:
(1) RBCs coated with only IgG,
(2) RBCs coated with IgG and complement
components, and
(3) RBCs coated with complement components
without detectable immunoglobulins (When the
RBCs are coated chiefly with complement
proteins, a positive DAT depends upon the
presence of anticomplement (principally anti-C3)
in the antiglobulin reagent.)

62. Therapy
• General: Transfusion.
• Therapy of Warm-Antibody Autoimmune Hemolytic
Anemia:
1. Glucocorticoids
2. Splenectomy
3. Rituximab
Rituximab is a monoclonal antibody directed against the
CD20 antigen expressed on B lymphocytes and used for
treatment of B cell lymphoma. It eliminates B lymphocytes,
including presumably those making autoantibodies to RBCs.
4. Immunosuppressive Drugs
5. Cytotoxic drugs such as cyclophosphamide to suppress
synthesis of autoantibody.

63. • Therapy of Cold-Antibody Hemolytic Anemia
1. Keeping the patient warm, particularly the
patient's extremities, is moderately effective in
providing symptomatic relief.

64. • Therapy of Drug-Immune Hemolytic Anemia
1. Discontinuation of the offending drug often is the only
treatment needed. This measure is essential.
2. the drug need not be discontinued because of a
positive direct antiglobulin reaction alone but only in
the presence of overt hemolytic anemia.

65. Alloimmune Hemolytic Disease of the
Newborn
• Alloimmune hemolytic disease of the fetus and
newborn is caused by the action of transplacentally
transmitted maternal immunoglobulin IgG antibodies
on paternally inherited antigens present on fetal red
cells but absent on the maternal red cells.
• Maternal IgG antibodies bind to fetal red cells, causing
hemolysis. As a consequence of the hemolytic process,
anemia, extramedullary hematopoiesis, and neonatal
hyperbilirubinemia sometimes result in fetal loss or
neonatal death or disability.

66. Definition
erythroblastosis fetalis was caused by immunization
of an Rh-negative mother by the red blood cells
from an Rh-positive fetus.
Antibodies produced by the sensitized mother
crossed the placenta in the next pregnancy and
coated the fetal Rh-positive cells, leading to
hemolysis and thus to anemia, hydrops, and
severe neonatal jaundice secondary to hemolysis.

67. Hemolytic Disease of the New born (HDN)
2. Incompatibilities with in the Rh blood group system
Allo-immune hemolytic anemia
Subsequent pregnancies
Maternal anti-Rh antibodies IgG type
Pass placental barrier
Enter fetal circulation and destroy fetal red cells
(agglutination and hemolysis)
Placenta
Uterus

68. • Postpartum and antepartum anti-D prophylaxis to
prevent Rh sensitization led to the most dramatic
reduction in the incidence of Rh hemolytic disease
of the newborn.

69. • Other than the Rh blood group system
However, the disease has not disappeared, and cases
of HDN resulting from red cell Abs directed toward
Ags other than the Rh blood group system are being
increasingly recognized.

70. Etiology and Pathogenesis
Causative Antibodies
• More than 40 different red cell antigens are associated
with maternal alloimmunization.
• These antibodies can be categorized into three main
classes:
(1) antibodies directed against the D antigen in the Rh
blood group system,
(2) antibodies directed against the A and B antigens, and
(3) antibodies directed against the remaining red cell
antigens (non-D Rh antibodies (c, C, e, E, cc, and Ce)
and antibodies belonging to the Kell, Duffy, Kidd, and
MNS systems ).

71. 1.Rh Hemolytic Disease
• Immunization:
1. Asymptomatic transplacental passage of fetal red cells occurs in 75%of
pregnant women at some time during pregnancy or during labor and
delivery.
2. The presence of D-positive red cells in a D-negative mother initially
provokes a primary immune response that is weak and slow and consists
of IgM antibodies that do not cross the placenta.
3. Subsequently, anti-D IgG antibodies capable of crossing the placenta are
produced.
4. Repeated exposure to Rh-positive fetal red blood cells, as in a second Rh-
positive pregnancy in a sensitized Rh-negative woman, produces a
secondary immune response marked by rapid production of large
amounts of anti-D IgG antibody by maternal memory B lymphocytes.

72. • In the absence of Rh Ig prophylaxis, sensitization
occurs in
– 7 to 16% of women at risk, after delivery of the first Rh-
positive ABO-compatible fetus,
– 2 % after delivery of an ABO-incompatible fetus.
• The reason why most women who are at risk for
development of anti-D are not sensitized is unclear.

73. • Hemolysis
Binding of transplacentally transferred maternal anti-
D IgG Abs to D-antigen sites on the fetal red cell
membrane is followed by
adherence of the coated RBCs to the FcR of
macrophages leading to
extravascular noncomplement-mediated lysis in the
spleen.

74. The blood film of a baby with Rh haemolytic
disease of the newborn showing spherocytosis

75. 2.ABO Hemolytic Disease
• ABO hemolytic disease of the newborn is limited to
mothers who are blood group type O and whose
babies are group A or B.
• Although far more common than Rh hemolytic
disease of the newborn, ABO hemolytic disease of
the newborn usually is mild.

76. • may affect the first-born ABO incompatible infant
because IgG anti-A and anti-B antibodies may be present normally in
group O adults.
• The low incidence of ABO hemolytic disease of the
newborn may be because most anti-A and anti-B antibodies are of
the IgM type incapable of crossing the placenta.
• Only a small proportion of group O individuals produce
anti-A and anti-B of the IgG type that can cross the
placenta.

77. The blood film of a baby
with ABO haemolytic disease of the
newborn showing marked
spherocytosis and an NRBC

78. 3.Hemolytic Disease Caused by Other
Red Cell Antibodies
When the D antibodies are excluded,
• the non-D Rh antibodies (E, C, and c) and
• those belonging to the Kell, Duffy, Kidd, and MNS
systems are most frequently involved.

79. Clinical Features of HDN
• Hallmarks of hemolytic disease of the newborn:
1. Anemia,
2. jaundice, and
3. hepatosplenomegaly
• An important complication of elevated serum
indirect bilirubin in the neonate is bilirubin
encephalopathy (kernicterus)is caused by bilirubin
pigment deposition, leading to neuronal necrosis,
marked by lethargy, poor feeding, and hypotonia.

80. Prevention of HDN
• Transfusion of blood compatible not only with the D
antigen but also with Kell and other Rh antigens for
premenopausal women to prevent alloimmunization.
• Use of Rh Ig is the mainstay of prevention of maternal
D immunization. (Postpartum nonsensitized Rh-
negative women who deliver an Rh-positive infant).
• Every obstetric patient should undergo ABO and RhD
typing and be tested for irregular serum antibodies at
the initial prenatal visit.

81. • However 1.8 % of Rh-negative women
apparently are sensitized from small
transplacental hemorrhages during pregnancy.
• Antepartum Rh Ig prophylaxis at 28 weeks'
gestation (this is the current standard
recommendation in the United States).

82. • The mechanism by which Rh Ig prevents
sensitization to the D antigen is not
understood.
• One theory proposes passively administered
anti-D attaches to the D-antigen sites on Rh-
positive red blood cells in the circulation and
interferes with the host's primary immune
response to the foreign antigen.

83. Hemolytic Anemia Resulting from
Chemical and Physical Agents
1. Arsenic, lead, copper, chlorates, and a variety of other
chemicals can cause severe red cell destruction.
– Arsenic may cause hemolysis by interacting with sulfhydryl
groups.
– Lead inhibits a variety of red cell enzymes, including several
enzymes of porphyrin metabolism and pyrimidine 5'-
nucleotidase. The anemia that it produces is usually not
primarily hemolytic in nature.
– Copper inhibits a number of red cell enzymes and catalyzes the
oxidation of intracellular reduced glutathione (GSH).
– Chlorates produce methemoglobin and Heinz bodies.
2. Many drugs: by poorly defined mechanisms.
3. Animal toxins, such as those of insects, spiders, and snakes.
4. Severe burns, probably as a result of direct damage to
erythrocytes by heat.

84. Hemolytic Anemia Resulting from
Infections with Microorganisms
1. Malaria, Babesia, and Bartonella, which directly invade the
erythrocyte.
• Malaria is probably the most common cause of hemolytic anemia.
• Falciparum malaria, in particular, can cause severe fatal hemolysis
(blackwater fever).
2. Other organisms cause hemolytic anemia by producing a
hemolysin (e.g., Clostridium Welchii),
3. by stimulating an immune response (e.g., Mycoplasma
pneumoniae),

85. Organisms causing haemolytic anemia
1. Cytomegalovirus
2. Epstein-Barr virus
3. Hepatitis A, B, C
4. Human immunodeficiency virus
5. Influenza A virus
6. Parvovirus B19
7. Plasmodium falciparum
8. Salmonella

86. Red cell fragmentation syndromes
• These arise through physical damage to red cells either
1. on abnormal surfaces (e.g. artificial heart valves or
arterial grafts),
2. arteriovenous malformations
3. or as a microangiopathic haemolytic anaemia.
This is caused by red cells passing through abnormal
small vessels due to
– deposition of fibrin associated with DIC or
– platelet adherence as in TTP or
– vasculitis as PAN (endoth damage).

88. • Microangiopathic hemolytic anemia:
In childhood, the commonest cause is
 enteric infection, most often by a verocytotoxin
secreting Escherichia coli, resulting in HUS.
In adults, the commonest causes are
 idiopathic TTP,
 pregnancy-associated hypertension
 carcinoma.

89. • Blood film and count
1. microspherocytes, keratocytes and schistocytes
2. polychromasia.
3. In microangiopathic HA, there is associated
thrombocytopenia and large platelets.

90. • In the postdiarrhoeal HUS of childhood there is
leucocytosis and neutrophilia,
– the severity of which correlates with associated renal
damage.
• Blood films of microangiopathic HA and of
haemolytic anaemia caused by large vessel or
valvular diseases or prostheses cannot be readily
distinguished.

91. • Haemolysis in the microangiopathic and mechanical
haemolytic anaemias is intravascular the resultant
haemoglobinuria can lead to complicating iron deficiency,
the features of which are then apparent on the blood film.
• It should be noted that, although red cell fragmentation is
often a feature of chronic DIC, it is quite uncommon in
acute DIC. Examination of a blood film is therefore not a
useful screening test if this diagnosis is suspected.
• Conversely, blood film examination is very important if TTP
or HELLP syndrome is suspected.

92. Further tests
• The speedy recognition of HUS by the lab is of critical importance
for optimal management.
• assess the severity of haemolysis:
– Bilirubin and
– LDH estimations
– reticulocyte count
• Demonstrate intravascular haemolysis in chronic mild cases:
– detection of haemosiderin in urinary sediment

93. March haemoglobinuria
• This is caused by damage to red cells between
the small bones of the feet, usually during
prolonged marching or running. The blood
film does not show fragments.

94. mechanical haemolytic anaemia, due
to a defective prosthetic mitral valve,
showing numerous fragments

95. The blood film of an Afro-
Caribbean patient with iron
deficiency as a complication of
mechanical haemolysis from a
defective prosthetic valve. The film
shows fragments, hypochromia,
microcytosis and one target cell. The
patient also had haemoglobin C trait.

96. Several keratocytes (in microangiopathic haemolytic anaemia);
keratocytes are sometimes called ‘bite cells’

97. Several schistocytes including a
microspherocyte in HUS

98. The blood film of a patient with PNH showing polychromatic
macrocytes

99. The blood film of a patient with terminal liver disease of
unknown aetiology showing numerous acanthocytes (‘spur cell’
haemolytic an)

100. Hypersplenism
Hypersplenism usually is associated with the
triad of:
1. splenomegaly,
2. blood cytopenias, and
3. compensatory marrow hyperplasia;
it is characteristically corrected by splenectomy.

101. Causes of Massive Splenomegaly:
1. Chronic myeloid leukemia
2. Gaucher disease
3. Hairy cell leukemia
4. Idiopathic and secondary myelofibrosis
5. Leishmaniasis (kala azar)
6. Lymphoma
7. Malaria
8. Thalassemia major

102. Laboratory Features
• The blood cell morphology usually is normal,
although a few spherocytes may result from
metabolic conditioning of red cells during
repeated slow transits through the expanded
red pulp.

103. Miscellaneous causes of acquired
haemolytic anaemia
Haemolytic anaemia with
• a negative direct and indirect antiglobulin test
and with
• no specific morphological features
has been described as a transient phenomenon,
sometimes accompanied by
thrombocytopenia, in patients with hepatitis C
infection.

105. Anemia Algorithm
• Patient with anemia and increased reticulocyte count-
What is the result of a Coomb’s test ??
Extrinsic red
cell defect
Vessel Valve
Toxin
Negative Positive
(autoimmune hemolytic anemia)
Intrinsic red
cell defect
Membrane
Hemoglobin
Cytoplasm
“Warm” “Cold”

106. Hemolytic Anemia with Intravascular
Hemolysis
1. Mechanical damage (Microangiopathic
hemolytic anemia)
2. Chemical damage (Burns)
3. Infection (Malaria)
4. Transfusion reaction (ABO incompatibility)

107. Hemolytic Anemia with Extravascular
Hemolysis (RES)
1. Hereditary
• Hemoglobinopathies (sickle cell anemia)
• Enzymopathies (G6PD deficiency)
• Membrane defects (hereditary spherocytosis)
2. Acquired
• Immune mediated
– Autoimmune hemolytic anemia
• Nonimmune mediated
– Spur cell hemolytic anemia

108. • MCQ 5 An increased cold agglutinin titre is a
recognized feature of
(a) Non-Hodgkin’s lymphoma
(b) Paroxysmal nocturnal haemoglobinuria
(c) Mycoplasma pneumoniae infection
(d) Alpha-methyl dopa-induced haemolytic
anaemia
(e) Infectious mononucleosis

109. • MCQ 8 A positive direct antiglobulin
(Coombs’) test is characteristic of
(a) Hereditary spherocytosis
(b) Hereditary elliptocytosis
(c) Haemolytic disease of the newborn
(d) Delayed haemolytic transfusion reaction
(e) Warm autoimmune haemolytic anaemia

110. • Q10 The following are usually associated
with spherocytes in the blood film:
1 Severe iron deficiency anaemia
2 Combined deficiency of vitamin B12 and folic
acid
3 Severe burns
4 Autoimmune haemolytic anaemia
5 Polycythaemia rubra vera