Anaemia Flashcards
Principles of haemolytic anaemia
Red cell destruction and extra/intravascular haemolysis
**Red cell destruction
**removed from the circulation at the end of their lifespan (120 days)
Destroyed within the reticuoendothelial system (spleen, liver, bone marrow)
**Extravascular haemolysis
**Occurs predominantly in the reticuloendothelial system
Plasma free haemoglobin concentration is bareley increased
**Intravascular haemolysis
**Plasma haemoglobin concentration increases
Often a combination of both mechanisms
Haemolytic anaemia - causes of red cell destruction
**Defects within RBCs
**Dysfunction of enzyme - controlled mechanism
Abnormal haemoglobins e.g. haemoglobin S in sickle cell anaemia
Thalassaemia
**Loss of structural integrity of membrane and cytoskeletn
**Hereditary spehrocytosis and herediatry eliptocytosis
Paroxysmal noctural haemoglobinuria
Immune adn drug-associated antibody damage
**Damage by extrinsic factors
**Mechanical trauma e.g. heart valve
Microangiopathic conditions
Chemical factors
Notes on these images
**Spheocytes
**Absence of a pale centre
**Fragmented red cells
**Seen in MAHA
**Blister cells
**Oxidative damage to red cell
Feautres of bone marrow compensation in haemolytic anaemia
Polychromatic red cells -> reticulocytes
Nucleated red cells seen in acute blood loss and haemolytic anaemia
Symptoms and signs of rd cell destruction
Jaundice
Intravascular haemolysis -> dark urine from haemoglobinuria or haemosiderinuria
**Investigations
**Bilirubin (elevation of unconjugated bilirubin with normal direct bilirubin)
Raised LDH
**Investigations confirming release of haemoglobin from damaged RBCs
**Decreased serum haptoglobins
Presence of methaemalbuminaemia (when haptoglobins saturated)
Haemoglobinuria and haemosiderinruia in intravascular haemolysis
Notes on diagnosis of suspected hereditary haemolytic anaemia
- Hereditary spherocytosis -> flow cytometry EMA dye binding test or osmotic fragility determination
- G6PD deficiency (enzyme in pentose phosphate pathway, maintains levels of NADPH)
- Red cell pyruvate kinase assay (enzye involved in final step in glycolysis) (AR and AD inheritance - AR more common)
- Other red cell enzymes involved in glycose
- Thalassaemia - estimation of percentage of haemoglobin A2, and F
- Tests for sickle cell anaemia (electrophoresis)
- Examination of the proteins of the red cell membrane and cytoskeleton by gel electrophoresis
Diagnosis/investigations of presumed acquired haemolytic anaemia
**Suspected autoimmune
**DAT
Tests for autoantibodies in patient serum
Demonstration of thermal range of autoantibodies
**Drug induced haemolytic anaemia
**Screening test for G6PD
**Mechanical stress suspected
**Red cell morphology, platelet count, renal function tests, coagulation screen, fibrinogen assay, test for fibrinogen/fibrin degradation products
**Obscure cases -> test for PNH
**Flow cytometry of erythrocyte and neutrophil glycoslphosphatidyllonositol (GPI)-linked antigens
DAT and differentials
Principles of direct antiglobulin test
**Principles of direct antiglobulin test
**Peripheral blood collected from patient, spun and red cells separated from plasma
Red cells coated with antibodies resuspecded in saline, anti human Ig and anti complement antibody added to suspended red cells. Anti-human Ig and anti complement antibody will bind to any autoantibodies present in red cells and agglutination then observed
Principles of indirect antiglobulin test
Peripheal blood collected and spun and separated
Plasma with free anti-RBC antibody used. Group O human blood cells added to the plasma. The autoantibody binds to the human RBCs that have been added to the plasma
Anti human Ig and anti human complement antibody are added -> bind to the autoantibody which is attached to the group O human blood cells and agglutination is oberserved
Notes on G6P6 deficiency
- X linked recessive inborn error of metabolism. Homozygous females affected
- Predisposes to haemolysis
- Causes jaundice in response to a number of triggers - foods (fava beans), intercurrent infection, naphthalene or oxidant drugs
- Greece and Middle East - 35-40% males
- Low levels of G6PD -> enzyme involved in pentose phosphate pathway
**Blood film
**Irregularly contracted cells
Heinz bodies
Bite cells -> removal of Heinz bodies by spleen
Hemi-ghost cells - Hb retracted to one side of cell
Features of hyposplenism when RES overloaded
Polychromatic macrocytes
**Differential -> **Other causes of on-spherocytic haemolysis with enzyme deficiencies e.g. pyruvate kinase
Notes on warm haemolytic anaemia
- Usually IgG - directed at RBC membrane antigens
- Removal of pieces of membrane -> spherocytes
- Blood film -> polychromatic macrocytes, severe -> nucleated red blood cells and hyposplenic changes
- Differential -> inherited spherocytosis (DAT will be negative, +ve in warm autoimmune haemolytic anaemia)
Notes on cold autoimmune haemolytic anaemia
- Usually IgM
- Red cell agglutination and complement haemolysis
- Causes -> infectious mononucleosis and mycoplasma
- Clonal production of cold-agglutinin cold haemagglutinin disease “CHAD”
- Blood film -> red cell agglutination (differentiates from warm), spherocytes and polychromasia
Causes of MAHA
- Non immune group of acquired haemolytic anaemia
- Red cell fragmentation due to endothelial pathology in the presence of platelet or fibrin thrombi in the ciruculation
- Blood film -> keratocytes/horn cells, schistocytes/helmet cells and micro spherocytes.
- Platelets consumed -> thombocytopaenia
- Bone marrow response with reticulocytosis and polychromatic cells in peripheral blood film
**Causes
**Vave haemolysis (prosthetic cardiac valves)
HUS - enterohaemorrhagic (Shiga toxin producing) E. coli
TTP
- Idiopathic/autoantibody mediated
- Results from reduced processing of ADAMTS-13, a metalloprotease responsible for processing of von Willebrand’s factor in the circulation
Associated with pregnancy
- Pre-eclampsia
- HELLP
Pathology and features of TTP
**Pathology
**Intravascular hyaline (platelet rich) thrombi
Terminal arterioles and capillaries
Distinct from DIC - fibrin rich thrombi
**Classic pentad
**Fever
MAHA
Thrombocytopaenia
Neurological symptoms and signs
Renal function abnormalities
**Current dyad - broaded definition as effective treatment given early
**MAHA
Thromvocytopaenia
**Differentiating HUS from TTP
**Renal failure more dominant in HUS
ADAMTS 13 -> normal in HUS, low in famillial TTP and idiopathic seocndayr to autoantibody.
If autoantibody -> steroids and targeted immune therapy (rituximab)
Can also do assays for ultra-high molecular weight vWF multimers (TTP)
TTP - notes on normal processing of Von Willebrand’s factor
Endothelial cell containing Weibel-Palade bodies which contain vWF -> released into subendothelial matrix. Also released into blood
ADAMTS 13 will normally cleave ultra large multimers of vWF and the clotting cascade will not be activated
In TTP - either an autoantibody to ADAMTS 13 or, as a consequence of an inherited deficiency, decreased levels of ADAMTS 13 -> deposition of uncleaved ultra large multimers of vWF on endothelial surface which activates platelets and leads to the formation of platelet rich thrombi
Pathology of epidemic HUS - Shigatoxin producing E.coli
Shiga toxin binds to the glycospingolipid receptor -> activates endothelin 1 -> vasoconstriction and acute renal failure
Shiga toxin -> neutrophil activation -> damages glomeruli endothelial cell -> formation of thrombus
Notes on alpha thalassaemia
- Impaired production of alpha chains leading to excess beta chains -> haemolysis
- Genes encoded on chromosome 16 - inherit 4 genes total (2 from each chromosome)
** Diagnosis
** HbH bodies = beta tetrameers
Excess gamma chains -> gamma tetramers = Hb Barts
**Silent carrier
**Heterzygous for one gene deletion, common in Maori, SEA, Africa
Hb normal/slightly reduced, MCV borderline
HbH bodies difficult to find, gamma tetramers in 70%
No reproductive issues
** 2 gene deletion = trait
** Mild anaemia, MCV 65-75
HbH bodies usually detectable in –/aa. Often detect gamma tetramers
Reproductive implications for –/aa *more common in SEA
**3 gene deletion = HbH disease
** Excess beta chains = beta tetramers
Membrane damage and chronic haemolysis
Moderate anaemia usually 70-100 , MCV 50-65
Some require transfusion or get iron overload
**4 gene deletion = Hb Barts
** Gamma tetramers
Foetal or early postnatal death
Early detection important to avoid maternal complictions due to large placenta (toxaemia, post-partum haemorrhage)
