Haematology Flashcards
What is the defining characteristic of a stem cell?
Stem cells can self-renew as they have the ability to divide into 2 cells with different characteristics: one another stem cell; the other capable of differentiating to mature progeny.
Normal erythropoiesis requires erythropoietin. Where are the endogenous erythropoietin production sites?
90% from juxtatubular interstitial cells in the kidney in response to hypoxia.
10% from hepatocytes.
Briefly name the key cells in erythropoiesis.
Myeloid stem cell –> proerythroblast –> erythroblast –> erythrocyte.
Name some cytokines required in the production of granulocytes and monocytes.
G-CSF (granulocyte colony-stimulating factor); GM-CSF (granulocyte-macrophage colony-stimulating factor); M-CSF (macrophage colony-stimulating factor) and various interleukins.
What are granulocytes?
A category of leukocytes with granules in their cytoplasm (e.g. neutrophil, basophil, eosinophil).
Briefly describe the function of platelets.
They survive around 10 days in circulation and have a role in primary haemostasis. They contribute phospholipid, which promotes blood coagulation.
Define anisocytosis and poikilocytosis.
Anisocytosis is where erythrocytes show more variation in size than is normal.
Poikilocytosis is where erythrocytes show more variation in shape than is normal.
What is a microcyte?
An erythrocyte which is smaller than normal. A blood sample shows MICROCYTOSIS. Contrasts with macrocytosis and macrocytes.
Why do normal erythrocytes have a central pallor which extends roughly 1/3 of the diameter?
Due to the disc shape of the erythrocyte which means there is less haemoglobin in the centre.
Define hypochromia.
Erythrocytes with a larger area of central pallor than normal, due to less haemoglobin or a flatter cell. These cells are described as hypochromic and are often microcytic.
Define hyperchromia.
Erythrocytes which lack central pallor, because they’re thicker than normal or because their shape is abnormal. Described as hyperchromic or hyperchromatic.
What are the two most important types of hyperchromic erythrocytes?
Spherocytes: cells approximately spherical in shape. These result from the loss of cell membrane without the equivalent loss of cytoplasm.
Irregularly contracted cells are irregular in outline but smaller than normal cells. Usually result from oxidant damage to the cell membrane and the haemoglobin (e.g. in glucose-6-phosphate deficiency).
How can you detect young erythrocytes on blood films?
Look out for polychromic cells. Polychromasia describes an increased blue tinge to the cytoplasm of the erythrocyte, indicating the cell is young.
Do a reticulocyte stain. Exposes living erythrocytes to methylene blue which precipitates as a network or “reticulum”. Identification of reticulocytes more reliable for counting than polychromasia.
Give 6 types of poikilocytes.
Fragments (schistocytes), spherocytes, irregularly contracted cells, sickle cells, target cells and elliptocytes.
Describe target cells.
Cells with an accumulation of haemoglobin in the centre of the area of central pallor. They occur in obstructive jaundice, liver disease, haemoglobinopathies and hyposplenism.
What can cause the presence of elliptocytes?
Hereditary elliptocytosis or iron deficiency.
Contrast rouleaux and agglutinates.
Rouleaux are stacks of red cells, which resemble piles of coins, resulting from alterations in plasma proteins.
Agglutinates are irregular stacks rather than tidy stacks, usually resulting from antibody on the surface.
What is a Howell-Jolly body?
A nuclear remnant in an erythrocyte. Commonest cause is a lack of splenic function.
Define leucocytosis and leucopenia and neutrophilia and neutropenia.
Leucocytosis is too many leucocytes.
Leucopenia is too few leucocytes.
Neutrophilia is too many neutrophils.
Neutropenia is too few neutrophils.
What is left shift on a blood film?
An increase in non-segmented neutrophils (band cells) or that there are neutrophil precursors in the blood.
What are the causes of toxic granulation (heavy granulation of neutrophils)?
What causes vacuolation?
Infection, inflammation and tissue damage.
Normal feature of pregnancy.
Vacuolation = bacterial infection
Define hypersegmented neutrophil and give possible causes.
An increase in the average number of neutrophil lobes or segments. Causes include a lack of vitamin B12 or folic acid.
How is a reference range derived and how can it be enumerated from a normal distribution?
A reference range is derived from a carefully defined reference population. Samples are collected from healthy volunteers with defined characteristics. Data with a normal distribution can be analysed by determining the mean and standard deviation and taking the mean +/- 2SD as the 95% range.
What is in a full blood count (FBC)?
White blood cell count (x10^9/l) Red blood cell count (x10^12/l) Platelet count (x10^9/l) Hb (haemoglobin concentration) (g/l) Hct (haematocrit) (l/l or %) MCV (mean cell volume) (fl) MCH (mean cell haemoglobin) (pg) MCHC (mean cell haemoglobin concentration (g/l)
How are white blood cell, red blood cell and platelet counts done?
By automated instruments which enumerate electronic impulses generated when cells flow between a light source and a sensor or when cells flow through an electric field.
How is haemoglobin concentration and haematocrit measured?
By an automated instrument which converts Hb to a stable form and measures light absorption at a specific wavelength.
Haematocrit is measured by centrifuging a blood sample.
How are MCV, MCH and MCHC calculated?
MCV = Hct / RBC (divide the total volume by number) MCH = Hb / RBC (amount of Hb in given volume of blood by number of cells) MCHC = Hb / Hct (amount of Hb in a given volume of blood by the proportion of the sample represented by erythrocytes).
In terms of MCHC, what does hypochromia indicate?
A low MCHC (hypochromia correlates with MCHC).
What components of a FBC would be raised in a subject with polycythaemia?
Haemoglobin concentration, red blood cell count and haematocrit are all increased compared with normal subjects of the same age and gender.
What is the cause of pseudopolycythaemia?
A reduced plasma volume.
What are the causes of true polycythaemia?
Inappropriately (tumour) or appropriately (hypoxia) raised erythropoietin levels.
Blood doping or over-transfusion.
Administering erythropoietin.
Polycythaemia vera.
What is polycythaemia vera?
An erythropoietin independent polycythaemia caused by an intrinsic bone marrow disorder. Can lead to hyperviscosity (thick blood), which can lead to vascular obstruction.
How can you treat polycythaemia?
If there is no physiological need for high haemoglobin concertation, or if the hyperviscosity is extreme, blood can be removed to thin the blood. If there’s an intrinsic bone marrow disease, drugs can be used to reduce bone marrow production of red cells.
What are the main mechanisms of anaemia?
Reduced production of erythrocytes/ haemoglobin in the bone marrow, loss of blood, reduced survival of erythrocytes, pooling of RBCs in an extra-large spleen.
What are the commonest causes of microcytic anaemia?
Defect in haem synthesis: iron deficiency.
Defect in globin synthesis (thalassaemia) - either A or B thalassaemia depending upon whether it is the A or B chain which is affected.
ACD.
Give mechanisms behind major causes of macrocytic anaemia.
Abnormal haemopoiesis: red cell precursors continue to make Hb and other proteins but fail to divide normally. Eg megaloblastic erythropoiesis which refers to a delay in maturation of the nucleus while the cytoplasm continues to grow.
Premature release of cells from bone marrow as young red cells are around 20% larger - for example a recent major blood loss with adequate iron stores would cause reticulocyte release.
Give mechanisms of normocytic anaemia.
Recent blood loss, failure in RBC production, pooling in spleen.
What is haemolytic anaemia?
Anaemia resulting from shortened survival of erythrocytes in circulation. Can result from intrinsic abnormalities of RBCs or extrinsic factors affecting them.
Contrast intravascular and extravascular haemolysis.
Intravascular haemolysis occurs if there’s very acute damage to the erythrocyte.
Extravascular haemolysis occurs when defective red cells are removed by the spleen.
When would you suspect haemolytic anaemia?
Otherwise unexplained, normochromic and normocytic or macrocytic anaemia.
Evidence of morphologically abnormal erythrocytes,
Evidence of increased RBC breakdown or increased bone marrow activity.
Give inherited causes of haemolytic anaemia.
Hereditary spherocytosis (affects membrane). Sickle cell anaemia (affects the Hb) Pyruvate kinase deficiency (affects the glycolytic pathway) Glucose-6-phosphate deficiency (affects the pentose shunt, renders the erythrocytes susceptible to oxidant damage).
Give acquired causes of haemolytic anaemia.
Autoimmune haemolytic anaemia - attacks membrane.
Drugs and chemical (oxidants).
Microangiopathic haemolytic anaemia (leads to schistocytes).
Malaria.
Detail inherited spherocytosis.
A hereditary defect in the cell membrane which causes the cell to have part of its membrane removed in the spleen. This means the RBCs become less flexible and are then removed prematurely by the spleen (extravascular haemolysis). The bone marrow responds by increasing output, causing polychromasia and reticulocytosis. The increased Hb breakdown causes bilirubin to build up, causing jaundice and gall stones. The only effective treatment is splenectomy. A good diet/ a daily folic acid tablet is needed to prevent secondary folic acid deficiency.
Detail glucose-6-phosphate dehydrogenase (G6PD) deficiency.
G6PD is important in the protection of erythrocytes against oxidant damage. Oxidants may be generated in the blood (in infection) or may be exogenous. Usually results in severe intravascular haemolysis (as a result of infection or exposure to exogenous agents). These episodes are associated with considerable numbers of irregularly contracted cells. Also associated with Heinz bodies: round inclusions containing denatured haemoglobin. May require blood transfusion.
What are Heinz bodies?
Structures formed in glucose-6-phosphate dehydrogenase deficiency when erythrocytes are exposed to oxidants. They are round inclusions formed as haemoglobin denatures, which leave defects in the erythrocytes.
Detail autoimmune haemolytic anaemia.
Autoantibodies directed against RBC antigens. The immunoglobulin bound to the RBC is recognised by splenic macrophages, which remove parts of the cell membrane, leading to spherocytosis. This makes the erythrocytes less flexible. The combination of cell rigidity and recognition of antibody + complement on RBC surface leads to removal by spleen. Treatment included immunosuppressives and splenectomy if severe. Diagnosis involves the presence of spherocytes, detection of Ig + complement and the detection of autoantibodies.
Where is haem synthesised? Where are globin chains synthesised?
Haem is synthesised in mitochondria.
Globin is synthesised in ribosomes.
What are the globin chains in HbA, HbA2 and HbF?
HbA = A2B2 HbA2 = A2D2 HbF = A2Gamma2
Describe the primary, secondary and tertiary globin structure.
Primary: A = 141AA, non-A = 146AA.
Secondary: 75% helical arrangement
Tertiary: approximate sphere, hydrophilic surface, hydrophobic core, haem pocket.
What factors cause a right-shift in the haemoglobin-oxygen dissociation curve?
An increase in 2,3-DPG concentration, proton concentration (a decrease in pH), CO2 and HbS.
What is thalassaemia and what are its causes and inheritance patterns?
Thalassaemia is caused by defects in globin chain synthesis leading to reduced of absent production of the affected chain. It is classified based on the globin type affected.
It is also classified by severity: minor “trait”, intermedia (transfusion independent), major (transfusion dependent).
It follows an autosomal recessive mendelian inheritance.
Inheritance of 2B^0 genes gives rise to a major classification due to absence of synthesis. 2B^+ gives rise to an intermedia classification due to reduced synthesis,
What would the FBC and blood film of a patient with thalassaemia look like?
Thalassaemia leads to a microcytic, hypochromic blood picture IN THE ABSENCE OF IRON DEFICIENCY.
The RBC count is raised relative to Hb.
Target cells present with poikilocytosis but no anisocytosis.
In B-thalassaemia, HbA2 and HbF are raised.
In A-thalassaemia, HbA2 and HbF are normal, so you must make a presumptive diagnosis followed up with DNA analysis.
Describe the presentation and blood film of a patient with beta thalassaemia major.
Severe anaemia - incompatible with life without regular blood transfusions. Clinical presentation usually after 4-6 months of life. Hepatosplenomegaly due to extra-medullary haematopoiesis. Erythroid hyperplasia in bone marrow.
Blood film shows gross hypochromia, with microcytic erythrocytes and poikilocytosis (with target cells).
HbA2 and HbF raised.
What are the clinical features of B thalassaemia?
Chronic fatigue, failure to thrive, jaundice, delay in growth and puberty, skeletal deformity, splenomegaly, iron overload, cardiac failure.
Describe the treatment available for B thalassaemia sufferers.
Transfusions with phenotyped RBCs. Requires regular transfusions 2-4 weekly.
Iron chelation therapy: starts after 10-12 transfusions or when serum ferritin >1000mcg/l (iron accumulates due to repeated transfusions)
