2. DEFINITION AND CLASSIFICATION
Anaemias resulting from an increase in the rate of red
cell destruction.
Normally, red cells undergo lysis at the end of their
lifespan of 120±30 days within the cells of
reticuloendothelial (RE) system in
the spleen and elsewhere (extravascular haemolysis), and
haemoglobin is not liberated into the plasma in
appreciable amounts.
The red cell lifespan is shortened in haemolytic anaemia
i.e. there is accelerated haemolysis.
However, shortening of red cell lifespan does not
necessarily result in
anaemia.
In fact, compensatory bone marrow hyperplasia may
cause 6 to 8-fold increase in red cell production without
3. The premature destruction of red cells in
haemolytic
anaemia may occur by 2 mechanisms:
Firstly, the red cells undergo lysis in the circulation
and
release their contents into plasma (intravascular
haemolysis).
In these cases the plasma haemoglobin rises
substantially
and part of it may be excreted in the urine
(haemoglobinuria).
Secondly, the red cells are taken up by cells of the
RE
system where they are destroyed and digested
4. Extravascular haemolysis is more common than the
former.
Haemolytic anaemias are broadly classified into 2 main
categories:
I. Acquired haemolytic anaemias caused by a variety of
extrinsic environmental factors (extracorpuscular).
II. Hereditary haemolytic anaemias are usually the result
of
intrinsic red cell defects (intracorpuscular).
.
5.
6. CLASSIFICATION OF HAEMOLYTIC
ANAEMIAS
I. ACQUIRED (EXTRACORPUSCULAR)
A. Antibody: Immunohaemolytic anaemias
1. Autoimmune haemolytic anaemia (AIHA)
i) Warm antibody AIHA
ii) Cold antibody AIHA
2. Drug-induced immunohaemolytic anaemia
3. Isoimmune haemolytic anaemia
B. Mechanical trauma: Microangiopathic haemolytic anaemia
C. Direct toxic effects: Malaria, bacterial, infection and other
agents
D. Acquired red cell membrane abnormalities: paroxysmal
nocturnal haemoglobinuria (PNH)
E. Splenomegaly
7. II. HEREDITARY (INTRACORPUSCULAR)
A. Abnormalities of red cell membrane
1. Hereditary spherocytosis
2. Hereditary elliptocytosis (hereditary ovalocytosis)
3. Hereditary stomatocytosis
B. Disorders of red cell interior
1. Red cell enzyme defects (Enzymopathies)
i) Defects in the hexose monophosphate shunt: G6PD
deficiency
ii) Defects in the Embden-Meyerhof (or glycolytic) pathway:
pyruvate kinase deficiency
2. Disorders of haemoglobin (Haemoglobinopathies)
i) Structurally abnormal haemoglobins: sickle syndromes,
other haemoglobinopathies
ii) Reduced globin chain synthesis: thalassaemias
8. FEATURES OF HAEMOLYSIS
GENERAL CLINICAL FEATURES
1. Presence of pallor of mucous membranes.
2. Positive family history with life-long anaemia in
patients
with congenital haemolytic anaemia.
3. Mild fluctuating jaundice due to unconjugated
hyperbilirubinaemia.
4. Urine turns dark on standing due to excess of
urobilinogen in urine.
5. Splenomegaly is found in most chronic haemolytic
anaemias, both congenital and acquired.
6. Pigment gallstones are found in some cases.
9. LABORATORY EVALUATION
OF HAEMOLYSIS
1. Is there evidence of haemolysis?
2. What is the type of haemolytic mechanism?
3. What is the precise diagnosis?
findings are conveniently divided into the
following 4 groups:
10. I. TESTS OF INCREASED
RED CELL BREAKDOWN
1. Serum bilirubin—unconjugated (indirect) bilirubin is raised.
2. Urine urobilinogen is raised but there is no bilirubinuria.
3. Faecal stercobilinogen is raised.
4. Serum haptoglobin (α-globulin binding protein) is reduced
or absent.
5. Plasma lactic dehydrogenase (LDH) is raised.
6. Evidences of intravascular haemolysis in the form of
haemoglobinaemia, haemoglobinuria, methaemoglobinaemia
and haemosiderinuria.
11. II. TESTS OF INCREASED RED
CELL PRODUCTION
1. Reticulocyte count reveals reticulocytosis which is
generally early and is hence most useful initial test of
marrow
erythroid hyperplasia.
2. Routine blood film shows macrocytosis, polychromasia
and
presence of normoblasts.
3. Bone marrow shows erythroid hyperplasia with usually
raised iron stores.
4. X-ray of bones shows evidence of expansion of marrow
space, especially in tubular bones and skull.
12. III. TESTS OF DAMAGE TO
RED CELLS
1. Osmotic fragility is increased or decreased.
2. Autohaemolysis test with or without addition of
glucose.
3. Coombs’ antiglobulin test.
4. Electrophoresis for abnormal haemoglobins.
5. Estimation of HbA2.
6. Estimation of HbF.
7. Tests for sickling.
8. Screening test for G6PD deficiency and other
enzymes (e.g.
Heinz bodies test).
13. IV. TESTS FOR
SHORTENED RED
CELL LIFESPAN.
A shortened red cell survival is best tested by 51Cr
labelling method.
Normal RBC lifespan of 120 days .
shortened to 20-40 days in moderate haemolysis
and
5-20 days in severe haemolysis.
14. I. ACQUIRED
(EXTRACORPUSCULAR)
HAEMOLYTIC ANAEMIASA. IMMUNOHAEMOLYTIC ANAEMIAS
Immunohaemolytic anaemias are a group of anaemias
occurring due to antibody production by the body against its
own red cells.
Immune haemolysis in these cases may be induced by one of
the following three types of antibodies:
1. Autoimmune haemolytic anaemia (AIHA) characterised by
formation of autoantibodies against patient’s own red cells.
Depending upon the reactivity of autoantibody, AIHA is
further divided into 2 types:
i) ‘Warm’ antibody AIHA in which the autoantibodies are
reactive at body temperature (37°C).
ii) ‘Cold’ antibody AIHA in which the autoantibodies react
better with patient’s own red cells at 4°C.
15. 2. Drug-induced immunohaemolytic anaemia.
3. Isoimmune haemolytic anaemia in which the
antibodies are
acquired by blood transfusions, pregnancies and
haemolytic
disease of the newborn.
An important diagnostic tool in all cases of
immunohaemolytic
anaemias is Coombs’ antiglobulin test for
detection of incomplete Rh-antibodies in saline
directly (direct Coombs’) or after addition of
albumin (indirect Coombs’).
16. A. WARM ANTIBODY AIHA
1. Idiopathic (primary)
2. Lymphomas-leukaemias e.g. non-Hodgkin’s
lymphoma, CLL, Hodgkin's disease.
3. Collagen vascular diseases e.g SLE
4. Drugs e.g. methyldopa, penicillin, quinidine group
5. Post-viral
B. COLD ANTIBODY AIHA
1. Cold agglutinin disease
a) Acute: Mycoplasma infection, infectious
mononucleosis
b) Chronic: Idiopathic, lymphomas
2. PCH (Mycoplasma infection, viral flu, measles,
17. ‘WARM’ ANTIBODY AIHA
PATHOGENESIS.
Warm antibodies reactive at body temperature and
coating the red cells are generally IgG class antibodies
and occasionally they are IgA.
Human red cells coated with IgG antibodies are bound to
the surface of RE cells, especially splenic macrophages.
A part of the coated cell membrane is lost resulting in
spherical transformation of the red cells (acquired
spherocytosis).
Red cells coated with IgG along with C3 on the surface
further promote this red cell-leucocyte interaction,
accounting for more severe haemolysis.
The spleen is particularly efficient in trapping red cells
coated
with IgG antibodies. It is, thus, the major site of red cell
destruction in warm antibody AIHA.
18. CLINICAL FEATURES
Warm antibody AIHA may occur at any age and in
either sex.
The disease may occur without any apparent cause
(idiopathic) but about a quarter of patients develop
this disorder as a complication of an underlying
disease affecting the immune system such as
SLE, chronic lymphocytic leukaemia, lymphomas
and certain
drugs such as methyl DOPA, penicillin
The disease tends to have remissions and relapses.
1. Chronic anaemia of varying severity with
remissions and
relapses.
2. Splenomegaly.
19. LABORATORY FINDINGS.
1. Mild to moderate chronic anaemia.
2. Reticulocytosis.
3. Prominent spherocytosis in the peripheral blood film.
4. Positive direct Coombs’ (antiglobulin) test for
presence of warm antibodies on the red cell, best
detected at 37°C.
5. A positive indirect Coombs’ (antiglobulin) test at 37°C
may indicate presence of large quantities of warm
antibodies in the serum.
6. Unconjugated (indirect) hyperbilirubinaemia.
7. Co-existent immune thrombocytopenia along with
occasional venous thrombosis may be present (termed
Evans’ syndrome).
8. In more severe cases, haemoglobinaemia and
haemoglobinuria may be present.
20. ‘COLD’ ANTIBODY AIHA
PATHOGENESIS.
Antibodies which are reactive in the cold (4°C) may
induce haemolysis under 2 conditions:
1. Cold agglutinin disease. In cold agglutinin disease, the
antibodies are IgM type which bind to the red cells best
at
4°C.
These cold antibodies are usually directed against the I
antigen on the red cell surface. Agglutination of red
blood cells by IgM cold agglutinins is most profound at
very low temperature but upon warming to 37°C or
above, disagglutination occurs quickly.
Haemolytic effect is mediated through fixation of C3 to
the red blood cell surface and not by agglutination alone.
Most cold agglutinins affect juvenile red blood cells.
21. 2. Paroxysmal cold haemoglobinuria (PCH).
In PCH, cold antibody is an IgG antibody (Donath-
Landsteiner antibody)
which is directed against P blood group antigen and
brings
about complement-mediated haemolysis.
Attacks of PCH are precipitated by exposure to cold.
PCH is uncommon and may be seen in association with
tertiary syphilis or as a complication of certain
infections such
as Mycoplasma pneumonia, flu, measles and mumps.
22. CLINICAL FEATURES
1. Chronic anaemia which is worsened by exposure to
cold.
2. Raynaud’s phenomenon.
3. Cyanosis affecting the cold exposed regions such as
tips
of nose, ears, fingers and toes.
4. Haemoglobinaemia and haemoglobinuria occur on
exposure to cold.
Treatment consists of keeping the patient warm and
treating the underlying cause.
23. LABORATORY FINDINGS.
1. Chronic anaemia.
2. Low reticulocyte count since young red cells are
affected
more.
3. Spherocytosis is less marked.
4. Positive direct Coombs’ test for detection of C3 on the
red cell surface but IgM responsible for C3 coating on
red
cells is not found.
5. The cold antibody titre is very high at 4°C and very low
at 37°C (Donath-Landsteiner test).
24. ISOIMMUNE HAEMOLYTIC
ANAEMIA
Isoimmune haemolytic anaemias are caused by
acquiring
isoantibodies or alloantibodies by blood
transfusions,
pregnancies and in haemolytic disease of the
newborn.
These antibodies produced by one individual are
directed against red blood cells of the other.
25. B. MICROANGIOPATHIC HAEMOLYTIC
ANAEMIA
Microangiopathic haemolytic anaemia is caused by
abnormalities in the microvasculature.
It is generally due to mechanical trauma to the red
cells in circulation and is
characterised by red cell fragmentation
(schistocytosis).
There are 3 different ways by which
microangiopathic haemolytic anaemia results:
26. 1. EXTERNAL IMPACT. Direct external trauma to red
blood cells when they pass through microcirculation,
especially
over the bony prominences, may cause haemolysis
during various activities e.g. in prolonged marchers,
joggers,
karate players etc. These patients develop
haemoglobinaemia,
haemoglobinuria (march haemoglobinuria), and
sometimes myoglobinuria as a result of damage to
muscles.
2. CARDIAC HAEMOLYSIS. A small proportion of
patients who received prosthetic cardiac valves or
artificial
grafts develop haemolysis. This has been attributed to
27. 3. FIBRIN DEPOSIT IN MICROVASCULATURE.
Deposition of fibrin in the microvasculature exposes the
red cells to physical obstruction and eventual
fragmentation of red cells and trapping of the platelets.
Fibrin deposits in the small vessels may occur in the
following conditions:
i) Abnormalities of the vessel wall e.g. in hypertension,
eclampsia, disseminated cancers, transplant rejection,
haemangioma etc.
ii) Thrombotic thrombocytopenic purpura.
iii) Haemolytic-uraemic syndrome.
iv) Disseminated intravascular coagulation (DIC)
v) Vasculitis in collagen diseases.
28. D. PAROXYSMAL NOCTURNAL
HAEMOGLOBINURIA (PNH)
PNH is a rare acquired disorder of red cell
membrane in
which there is chronic intravascular haemolysis due
to undue
sensitivity of red blood cells to complement due to
defective
synthesis of a red cell membrane protein.
The defect affects all the cells of myeloid
progenitor lineage (RBCs, WBCs, platelets)
suggesting a deficient haematopoiesis.
The disorder generally presents in adult life.
29. PATHOGENESIS
PNH is considered as an acquired clonal disease of the
cell membrane while normal clone also continues to
proliferate.
The defect is a mutation in the stem cells affecting
myeloid progenitor cells that is normally required for
the biosynthesis of glycosyl phosphatidyl inositol (GPI)
essential for anchoring of the cell; the mutant form of
the gene is an X-linked gene called PIG-A
(phosphatidyl inositol glycan).
Thus, as a result of mutation, there is partial or
complete deficiency of anchor protein.
Out of about 20 such proteins described so far, the
lack of two of
the proteins—decay accelerating factor (DAF, CD55)
and a
membrane inhibitor of reactive lysis (MIRL, CD59),
30. CLINICAL AND LABORATORY
FINDINGS
ii) Pancytopenia (mild granulocytopenia and
thrombocytopenia frequent).
iii) Intermittent clinical haemoglobinuria; acute
haemolytic episodes occur at night identified by passage
of brown urine in the morning.
iv) Haemosiderinuria.
v) Venous thrombosis as a common complication.
The presence of inordinate sensitivity of red blood cells,
leucocytes and platelets to complement in PNH can be
demonstrated in vitro by Ham’s test using red cell lysis
at acidic pH or by sucrose haemolysis test.
