Red Cell Disorders 2 - Haemolytic Anaemia Flashcards
What is anaemia?
- Reduced oxygen carrying capacity.
- A reduction in the haemoglobin concentration of the blood below the normal for age and sex.
What is molecules/minerals are needed for erythropoiesis to occur in the body?
Iron
Vitamin B12
Folate
Erythropoietin
What can cause anaemia?
-Insufficient production of normal RBCS: iron deficiency, chronic renal disease, chronic inflammatory diseases
- Blood loss/ Haemorrhage
- Increased red cell destruction (Haemolysis)
What is the normal red cell lifespan?
120 days
What causes haemolytic anaemia?
Bone marrow should increase production of red cells several times to compensate for loss of red cells but-
Impaired erythopoiesis/ rate of rbc loss faster than erythropoietic activity of the bone barrow causes anemia to develop
Characterised by a reduced red cell span
Two classifications of haemolytic anemia
Inherited
Accquired
Inherited Haemolytic Anaemia Examples
Disorders of the red cell membrane
Haemoglobin disorders
Disorders of red cell enzymes
Acquired haemolytic anaemia examples
Antibodies, drugs, red cell fragmentation syndromes, trauma, chemicals.
2 Mechanisms of red cell destruction? Where do they occur? Example of diseases they are seen in.
Intravascular: Destruction occurs intravascularly, releasing Hb into the circulation. This process is not always abnormal, only when red cells are destroyed within the blood stream .
Extravascular: Destruction occurs in RE system e.g liver ans spleen. Abnormal when its seen in high amounts
Clinical Features of Haemolytic Anaemia
Reduced red cell survival
Other features apparent depending on the abnormality:
Anaemia.
Jaundice.
Splenomegaly.
Bone marrow expansion due to an increase in cellularity of the bone marrow and erythroid hyperplasia.
Laboratory Features of increased RBC breakdown
Raised serum bilirubin
Reduced haptoglobins
Laboratory Features of increased RBC production
Reticulocytosis
Laboratory features of damaged red cells
Spherocytes, red cell fragments
Specific enzyme defects etc.
Common Lab investigations for Haemolytic Anaemia
FBC
Blood film morphology
Reticulocytes
Bilirubin
LDH
Urinary haemosiderin
Urinary Hb
Haptoglobins
Direct Antiglobulin Test (DAT) – detects bound antibody
Inherited Haemolytic Anaemias - Hereditary Spherocytosis
- Red cell membrane defect
- most common hereditary haemolytic anaemia in Northen Europeans.
- Caused mainly by abnormalities of proteins involved in the vertical interactions betwen the membrane cytoskeleton and lipid bilayer – e.g: defects in Ankyrin spectrin complex and deficiencies in band 3.
Heredirary spehrocytosis - what does it look like under a microscope?
- Proportions of phospholipid bilayer are lost, decreasing the surface area and deformability of the cell (its ability to change shape) forming spherocytes.
- These cells are then removed in the spleen.
Heredirary Spherocytosis - Inheritance
Autosomal dominant with variable penetrance. Can be autosomal recessive but rare.
Hereditary Spherocytosis - Clinical Features
Anaemia – variable and can present in infancy or not until old age.
-Jaundice (fluctuates)
-Pigment gallstones
-Splenomegaly (common in most patients): Main form of treatment is therefore splenectomy
Diagnosis of straight forward HS cases:
- Family / clinical history
- FBC – Low Hb, raised MCHC, increased reticulocytes.
- Blood film - spherocytes
- Negative DAT
Diagnosis equivocal HS cases:
Equivocal cases: Few spherocytes/ no family history.
- Eosin-5-maleimide binding test - HS cells bind eosin-5-maleimide less well than normal cells.
- Gel Electrophoresis (SDS-PAGE)
- presence of microspherocytes on the peripheral blood film
Examples of other membrane defects
- Hereditary Elliptocytosis
- South - East Asian ovalocytosis
Function of red cells? What is required for this function?
- Function: To carry red cells
- Requirements: Energy in the form of ATP and a source of reducing power.
-Hexose monophosphate shunt (HMP) and anaerobic glycolysis are the only soruces of ATP and reducing power
What is reducing power needed for in red cells? What is needed for these functions to be carried out?
Convert methaemoglobin back to functional haemoglobin - Requires methaemoglobin reductase and NADH.
Counteract oxidative stresses e.g. removal of free oxygen radicals and hydrogen peroxide produced during infections.- Requires NADPH and glutathione (GSH).
Process of converting Methaemoglobin to funtional haemoglobin
- Glycolysis - conversion of glucose to lactate in the EM pathway ( Embden-Meyerhof (EM) pathway) results in production of ATP, NADH, 2,3-DPG.
- NADH used to MethHb reduction to haemoglobin.
Role of 2,3-diphopshocycerate in Hb. Enzyme deficiencies.
- Regulates Hb oxygen affinity - held between Beta chains keeping Hb in deoxy form.
- Clinical tolerance of enzyme deficiencies can be dependent on whether the deficiency is below / above 2,3 DPG production.
Hexose monophosphate pathway
Sole source of NADPH for maintaining levels of reduced glutathione (main antioxidant in red cells)
Production of NADPH catalysed by G6PD
G6PD Deficiency - Inheritance
- Most common inherited enzymopathy
- Sex linked inheritance
- > 100 variants with variable clinical presentation
- Hemizygous (male) or homozygous (female) individuals may be readily detected by screening tests, but it is more difficult to detect heterozygous (female) carriers.
G6PD deficiency - Where is it common? What does this deficiency protect against?
Common in tropical and subtropical regions.
Widely disseminated throughout Africa, the Mediterranean basin, the Middle East, Southeast Asia and indigenous populations of the Indian subcontinent.
Gives protection against P. Falciparum.
G6PD deficiency - Clinical Features
Often is asymptomatic.
Acute haemolytic anaemia in response to oxidant stress e.g. drugs, fava beans or infections. This can result in a rapid onset of intravascular haemolysis with haemoglobinuria.
Neonatal jaundice.
Chronic non-spherocytic haemolytic anaemia (CNSHA).
G6PD - Treatment
Treat underlying cause e.g. stop offending drug, infections.
Transfusions for severe anaemia.
Phototherapy/exchange transfusions for severe cases of neonatal jaundice.
G6PD Deficiency - Diagnosis
Blood film may show schistocytes and bite cells (features of intravascular haemolysis).
Hemighost cells may be present.
Heinz bodies (denatured haemoglobin) may seen with certain stains e.g. methyl violet and new methylene blue.
Enzyme screening assays e.g. fluorescent spot test – NADPH generated by G6PD fluoresces under a UV light.
Quantitative assays.
Autoimmune Haemolyti Anaemia (AIHA)
- Caused by immune system issues
- Can be warm or cold types
What is warm AIHA? What causes it?
- type of autoimmune hemolytic anemia where the immune system mistakenly targets and destroys red blood cells at normal body temperature (37°C or 98.6°F) - destroyed by macrophages in the RE system that hace Ig receptors.
- called “warm” because the immune-mediated hemolysis occurs optimally at body temperature.
- primarily caused by an autoimmune response, where the immune system produces antibodies (usually IgG) that target and attach to the person’s own red blood cells
Warm AIHA - Clinical Features / Blood Film Features
- Occurs at any age in any sex
- Results in haemolytic anaemia with variable severity.
- Splenomegaly is common.
- Blood film characterised by numerours spherocytes and polychromasia.
- Can be idiopathic or secondary e.g. CLL, SLE, infections.
AIHA diagnosis
Positive DAT - cells coated with antibody (usually IgG antibodies for warm, IgM for cold AIHA)/complement.
warm AIHA - Treatment
Treat underlying cause e.g. infection, remove drug.
Corticosteroids e.g. prednisolone .
Splenectomy - treats splenomeagly
Immunosuppression e.g. azathioprine, cyclophosphamide
Rituximab (anti CD-20) some success.
Folic acid and blood transfusions in in severe cases.
What is cold antibody AIHA
Antibody attaches to red cells in the peripheral circulation where the temperature is lower.
Antibody is usually IgM reacting at 40C (usually anti-I).
Clinical Features of cold AIHA / Blood film
- Results in chronic HA, aggravated by the cold.
- The antibodies fix complement resulting in both intravascular and extravascular haemolysis.
- Blood film – spherocytes less prominent but red cell agglutination present.
- DAT positive
Treatment for cold AIHA
Keeping patient warm
Treat underlying cause
Rituximab (especially if associated with a lymphoproliferative disorder)
What is Alloimmune HA
Produced by the patient and directed against foreign antigens ( immune system attacks and destroys red blood cells from a different individual, often due to differences in blood group antigens)
e,g transfused red cells, heamolytic disease of the fetus/newborn (HDFN)
What is drug induced immune HA
occurs as a result of the immune system’s reaction to certain medications.
- the immune system recognizes the drug or a drug-induced alteration of red blood cells as foreign and mounts an immune response, leading to the destruction of red blood cells.
3 mechanisms of drug induced immune haemolytic anaemia
-Antibody directed against a drug-red cell membrane complex (e.g. penicillin, ampicillin).
- Deposition of complement via a drug-protein (antigen)-antibody complex onto the red cell surface (e.g. quinidine, rifampicin).
- AIHA in which role of drug is unclear e.g. methyldopa.
Non-immune causes
- Arise due to physical/mechanical damage to red cells (often red cell fragmentation)
- Cardiac haemolysis e.g: prosthetic heart valves and grafts
- Microangiopathic causes: DIC, HUS/TTP
- Infections: malaria, clostridium perfringens septicaemia
- March haemoglobinuria: due to prolonged marching/running
- Chemical and physical agents: drugs such as dapsone
Thrombotic Thrombocytopaenic Purpura (TTP)
Features
Thrombocytopenia,
Microangiopathic haemolytic anaemia,
Neurological abnormalities,
Fever.
Thrombotic Thrombocytopaenic Purpura (TTP) - Pathology
Due to a deficiency of ADAMTS-13 metalloprotease which breaks down ultra large von Willebrand factor multimers that are strongly aggregative for platelets.
Widespread formation of microthrombi which can lead to multi-organ failure
Thrombotic Thrombocytopaenic Purpura (TTP) - Testing
Specialist test done to confirm TTP (ADAMTS-13).
