Acquired haemolytic anaemias Waggas Ahmed Elaas

Acquired Haemolytic anaemias are usually the result of an'extracorpuscular' or 'environmental' change. The defect comes from out side the red cells. They are classified generally into : Immune Haemolytic anaemias Non – immune Haemolytic anaemias

Classification Acquired Haemolytic anaemias : A. Immune hemolytic anemias 1. Autoimmune hemolytic anemia - caused by warm-reactive antibodies - caused by cold-reactive antibodies 2. Alloimmune hemolytic anemia -caused by hemolytic transfusion reaction - caused by hemolytic disease of newborn (HDN) 3. Drug associated B. Nonimmune hemolytic anemias 1. Chemical & physical agents (drugs, industrial, burns) 2. Infections (parasitic or bacterial : malaria, clostridia) 3. Red cell fragmentation syndromes - hemolytic - uremic syndrome (HUS) - thrombotic thrombocytopenic purpura (TTP) - prosthetic heart valves 4. Paroxysmal Nocturnal Hemoglobinuria (PNH)

Immune haemolytic anaemias Auto immune .H.A Autoimmtme haemolytic anaemias (AIHAs) are caused by antibody production by the body against its own red cells. They are characterized by a positive direct antiglobulin test (DAT) also known as the Coombs' test and divided into 'warm‘ and 'cold' types according to whether the antibody reacts more strongly with red cells at 37°C or 4°C. (typically 28- 31°C)

Direct Coomb's Test Is used to detect if antibodies or complement system factors have bound to RBC surface antigens in vivo. A blood sample is taken and the RBCs are washed (removing the patient's own plasma) and then incubated with antihuman globulin (also known as "Coombs reagent"). If this produces agglutination of RBCs, the direct Coombs test is positive, a visual indication that antibodies (and/or complement proteins) are bound to the surface of red blood cells.

Warm AIHA The red cells are coated with immunoglobulin (Ig), usually immunoglobulin G (IgG) alone or with complement, and are therefore taken up by RE macrophages which have receptors for the Ig Fc fragment. Part of the coated membrane is lost so the cell becomes progressively more spherical to maintain the same volume and is ultimately prematurely destroyed, predominantly in the spleen. Splenomegally – extravascular hemolysis – spherocytosis – Positive DAT

WAIHA : peripheral blood film showing spherocytes and large polychromatic cells

Cold AIHA The Autoantibodies are either monoclonal as in lymphoproliferative disorder, or Polyclonal as in infections (infectious mononucleosis) The Abs in cold AIHA are Usually IgM and bind to red cell at 28-31°C (mainly in the peripheral circulation where the blood temperature is cooled) Both intravascular and extravascular haemolysis can occur Mild jaundice and splenomegaly Spherocytosis is less marked

Monoclonal Abs : Polyclonal Abs : Are monospecific antibodies that are the same because they are made by identical immune cells that are all clones of a unique parent cell. Polyclonal Abs : Are antibodies that are obtained from different B cell resources. They are a combination of immunoglobulin molecules secreted against a specific antigen, each identifying a different epitope.

Alloimmune hemolytic anaemias In these types, antibody produced by one individual reacts with red cells of another. Two important situations are: Hemolytic transfusion reactions Hemolytic disease of the newborn Drug-induced immune hemolytic anaemias Antibodies directed against the drug (Antigen). The Ag-Ab complexes are deposited on red cells and make them lysed by macrophages of RE cells.

Non-Immune Hemolytic Anemias Hemolytic anaemias due to mechanisms or agents other than antibodies +/or complement e.g.: 1. Chemical & physical agents (drugs, industrial, burns) 2. Infections (parasitic or bacterial : malaria, clostridia) 3. Red cell fragmentation syndromes - hemolytic - uremic syndrome (HUS) - thrombotic thrombocytopenic purpura (TTP) - prosthetic heart valves 4. Paroxysmal Nocturnal Hemoglobinuria (PNH) Non-immune H.A Immune H.A Negative DAT Positive DAT

Heinz bodies oxidized denatured Hb. Appear as small round inclusions; and may appear as projections from the cell. They are found as a sign of either chemical poisoning, drug intoxication, (G6PD) deficiency, or the presence of an unstable Hb. They vary from 1 to 3 μm. One or more may be present in a single cell. They are usually close to the cell membrane.

Heinz bodies

Red cell fragmentation syndromes These arise through physical damage to red cells either on abnormal surfaces (e.g. artificial heart valves or arterial grafts), or as a microangiopathic haemolytic anaemia: This is caused by red cells passing through abnormal small vessels, due to deposition of fibrin and often associated with disseminated intravascular coagulation (DIC) or platelet adherence as in thrombotic thrombocytopenic purpura (TIP). The peripheral blood contains many deeply staining red cell fragments. Clotting abnormalities typical of DIC with a low platelet count are also present when DIC underlies the haemolysis.

Red cell fragmentation syndromes : Microangiopathic Hemolytic Anemia (Vascular abnormalities), showing schistocytes (fragmented cells)

Paroxysmal nocturnal haemoglobinuria (PNH) PNH is a rare, acquired, clonal disorder of marrow stem cells in which there is deficient synthesis of some protien structures in the red cell membrane. This render red cells sensitive to lysis by complement and the result is chronic intravascular haemolysis, classically at night because of the low blood pH. The urine is red due to the appearance of Hb. PNH is diagnosed by the acidified-serum lysis Test (or the Ham's Test). Recently, it is diagnosed by flow cytometry.

Laboratory diagnosis 1. Indirect diagnosis : not specific Reticulocytes count : increased Haptoglobin : Reduced Unconjugated Bilirubin : Increased Urine urobilinogen : Increased LDH : Increased 2. For intrvascular haemolysis Serum free Hb : present Methaemoglobinaemia Haemoglobinuria Haemosiderinuria 3. Specific tests : Coomb's test (DAT) : Positive in Immune HA Spherocytosis in autoimmune HA Osmotic fragility tests in spherocytosis Screening for G6PD deficiency in drug induced HA Ham's Test in PNH Staining for Heinz bodies