haemoglobinopathy Flashcards
- What is specialised language used to describe in haematology?
- What are some causes of microcytosis?
blood films and counts
Deficit in iron
anaemia of chronic disease
thalassaemia
- What is Beta-thalassaemia?
- What is Alpha-thalassaemia?
- What does the term ‘major’ refer to in terms of thalassaemia?
Defect in beta-globin chain synthesis
Defect in alpha-globin chain synthesis Significant impairment of globin chain (beta/alpha) synthesis
- What specific types can macrocytes be?
- What are some causes of macrocytosis?
Round, Oval, Polychromatic
Lack of vitamin B12 or folic acid Liver disease and ethanol toxicity Haemolysis (polychromasia) Pregnancy
- What portion of the red blood cell has less haemoglobin and is therefore paler?
- What does the term hypochromia refer to?
- What often comes with hypochromia?
A third of the diameter from the centre (less Hb therefore less red and more pale)
Means that eryhthrocytes have a larger area of central pallor than normal Microcytosis (iron deficiency and thalassaemia being common causes)
- What does the term polychromasia refer to?
- What does a blue tinge in a blood film indicate and why?
- What is polychromasia associated with?
Describes an inreased blue tinge to the cytoplasm of a red cell
That the red cell is young (reticulocyte) caused by stain methylene blue which stains for a higher RNA content Macrocytosis
- What is reticulocytosis?
- When may reticulocytosis occur?
- What does the term anisocytosis refer to?
Refers to the presence of increase numbers of reticulocytes
As a response to bleeding or red cell destruction (haemolysis) or response to treatment with iron, vitamin b12 and folic acid Red cells showing more variation in size than normal
- What does the term poikilocytosis refer to?
- What is meant by the haematocrit?
- What is meant by the packed cell volume?
Red cells showing more variation in shape than normal
Proportion of red blood cells in your blood, equivalent to the packed cell volume but not measured by centrifugation The proportion of a column of centrifuged blood occupied by red blood cells
What are target cells?
When do target cells occur?
accumulation of haemoglobin in the centre of the central pallour
dark dot seen in middle of cell
obstructive jaundice
liver disease
haemoglobinopathies-a group of recessively inherited genetic conditions affecting the haemoglobin component of blood.
hyposplenism- reduction in spleen function
what are sickle cells and how does its shape form
how does haemoglobin S occur
they are sickle or crescent shaped and they result from the polymerisation of haemoglobin S
in its deoxygenated form it is much less soluble than haemoglobin A
when one or two copies of abnormal beta globin gene (beta S) are inherited
mutation in beta globin gene causes a charged glutamic acid residue to be replaced by an uncharged valine molecule
what are schistocytes?
fragments of red blood cell, indicating a red blood cell has fragmented
may be caused by shearing process caused by platelet rich clots in small blood vessels eg disseminated intravascular coagulopathy
why is a reference range used
how is a reference range calculated
what are the caveats of reference ranges
need to know what is normal before you can interpret any clinical sign or lab test
get a sample of healthy volunteers
analyse them with the same instruments and techniques used for patient samples
data is analysed with an appropriate statistical technique
not all results within reference are normal
not all results outside of RR is abnormal
what mutation results in HbS
what properties of hbS means that it becomes sickle cell shaped?
missense mutation at codon 6 on the beta globin chain
charged glutamic acid is replaced by uncharged valine
deoxyhaemoglobin S is insoluble
causes it to polymerise to form tactoids that distort the RBC to a sickle shape
what diseases do sickle cell disease incorporate
Sickle Cell anaemia (hbSS)
a number of compound heterozygous states that lead to a disease syndrome due to sickling
eg HbSC
HbS beta thalassaemia
what are the two main pathogenesis of SCD
hypoxia leads to the polymerisation of HbS
results in the rigid sickling of rbcs which causes:
haemolysis of RBC and reduced RBC survival
- leads to gallstones and jaundice due to inc bilirubin
- leads to low Hb conc (anaemia)
- Aplastic crisis (Parvovirus 19 where bine marrow erythropoiesis has been shutdown - fine if rbc has a turnover of 120 days but if only 20 days- fatal)
Vasocclusion
- tissue damage, necrosis (infarction), pain, dysfunction
- in bones, kidney, brain, cerebral, retina, lung, spleen
Why is it that those with HbSS do not show signs of anaemia
HbS has a low affinity to 02
so gives up more oxygen- so body not 02 deprived
