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Y2 MCD - Haem, Labs, Microbio, Cancer, Immunology > HAEM; Lecture 6, 7, 8, 9 and 10 - Haemostasis, Abnormalities of haemostasis, The Hb molecule and thalassaemia, Blood transfusion, Sickle cell disease > Flashcards

HAEM; Lecture 6, 7, 8, 9 and 10 - Haemostasis, Abnormalities of haemostasis, The Hb molecule and thalassaemia, Blood transfusion, Sickle cell disease Flashcards

1
Q

Haem

How does a haemostatic plug form?

A

Response to injury -> vessel constriction, formation of unstable platelet plug (platelet adhesion and aggregation) -> stabilisation of plug with fibrin (blood coagulation) -> dissolution of clot and vessel repair (fibrinolysis)

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2
Q

Haem

What is the importance of vessel constriction in response to injury?

A

Important in small blood vessels; local contractile response to injury

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3
Q

Haem

What is the function of the endothelium?

A

Maintain barrier between blood and procoagulant subendothelial structures -> synthesis fo PGI2, thrombomodulin, vWF, plasminogen activators

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4
Q

Haem

How is the platelet formed?

A

Made from stem cell precursors which undergo nuclear replication to form megakaryocytes and become multinucleate, where they then mature with granulation and are released into circulation as megakaryocyte fragments - lives for 10 days

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5
Q

Haem

What are some ultrastructural features of the platelet?

A

Dense granules are important as they contain ADP; alpha granules contain vWF

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6
Q

Haem

How does platelet adhesion occur?

A

Platelet joins onto G1pIb and von Willebrand factor or directly from G1pIa to collagen which releases ADP and thromboxane -> both mechanisms exist due to different shapes of vessels and cells, to allow the adhesion to work no matter the situation

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7
Q

Haem

How does platelet aggregation occur?

A

Once platelet has attached to vWF/G1pIa and to collagen then due to release of ADP and thromboxane and thrombin it leads to joining of platelets using G1pIIb/IIIa and firinogen and Ca2+

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8
Q

Haem

How is prostaglandin metabolised in endothelial cells vs platelets?

A

The one in platelets occurs only when activated

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9
Q

Haem

Which antiplatelet agents are used as antithrombic agents?

A

ADP receptor antagonists (blocks receptor to stop rebinding), COX1 antagonist and GPIIb/IIIa antagonists

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10
Q

Haem

What is an example of COX-1 inhibitor?

A

Aspirin

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11
Q

Haem

What is an example of ADP receptor antagonist?

A

Clopidogrel, prasugrel

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12
Q

Haem

What is an example of GPIIb/IIIa?

A

Abciximab, tirofiban, eptifibatide

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13
Q

Haem

When are antiplatelet agents used?

A

Treatment of CVD; combination used during interventions - angioplasty, stents

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14
Q

Haem

What tests are used to monitor platelets and function?

A

Platelet count, bleeding tie and platelet aggregation

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15
Q

Haem

What is platelet count used for and what is the normal range?

A

Test used to monitor thrombocytopenia

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16
Q

Haem

What are symptoms of auto-immune thrombocytopenia?

A

Purpura, multiple bruises, ecchymoses

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17
Q

Haem

How do you carry out a haemostatic function of platelet test?

A

Normal bleeding time 3-8min, used to check platelet-vessel wall interaction when platelet count is normal (renal disease)

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18
Q

Haem

When testing platelet aggregation what is measured?

A

Functional defect of platelets e.g. vWF disease, inherited platelet defects

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19
Q

Haem

What are the sites of synthesis of clotting factors, fibrinolytic factors and inhibitors?

A

Liver, endothelial cells and megakaryocytes

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20
Q

Haem

What does the liver synthesise?

A

Most coagulation proteins

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21
Q

Haem

What do the endothelial cells synthesise?

A

vWF

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22
Q

Haem

What do megakaryocytes synthesise?

A

Factor V and vWF

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23
Q

Haem

Where does warfarin act on as an anticoagulant?

A
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24
Q

Haem

Where does warfarin act on as an anticoagulant?

A
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25
Q

Haem

What is Warfarin used for?

A

Long term anticoagulation following venous thrombosis and for treatment of atrial fibrillation

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26
Q

Haem

What is heparin used for?

A

Immediate anticoagulant in venous thrombosis and pulmonary embolism

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27
Q

Haem

What is the mechanism of action of Heparin?

A

Accelerates action of plasma inhibitor antithrombin which inhibits coagulation factors such as factor Xa and thrombin

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28
Q

Haem

What lab tests are used for blood coagulation?

A

APTT, PT, TCT/TT

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29
Q

Haem

What is APTT?

A

Activated partial thromboplastin time -> initiates coagulation hrough FXII and detects abnormalities in intrinsic and common pathways

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30
Q

Haem

What is PT?

A

Prothrombin time -> Initiates coagulation through tissue factor ad detects abnormalities in Extrinsic and common pathways

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31
Q

Haem

What is TCT?

A

Thrombin clotting time -> add thrombin and shows abnormality in fibrinogen to fibrin conversion

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32
Q

Haem

What tests are used for screening causes of bleeding disorders?

A

APTT and PT together

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33
Q

Haem

What test is used to monitor heparin therapy in thrombosis?

A

APTT

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34
Q

Haem

What test is used for monitoring warfarin treatment in thrombosis?

A

PT

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35
Q

Haem

How is a fibrin clot broken up?

A

Plaminogen reacts with tissue plasminogen activator forming plasmin which interacts with fibrin clot to form fibrin degradation products

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36
Q

Haem

Why does blood not clot completely whenever clotting is initiated by vessel injury?

A

Coagulation inhibitory mechanisms such as antithrombin and protein C anticoagulant pathway (with protein C and S) prevent this; with deficiencies in these factors are important risk factors for thrombosis

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37
Q

Haem

Where does antithrombin act on the anticoagulant pathway?

A
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38
Q

Haem

Where does protein C and S work on the anticoagulant pathway?

A
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39
Q

Haem

What are some minor bleeding symptoms?

A

Easy bruising, gum bleeding, frequent nosebleeds, bleeding after tooth extraction, post op bleeding, menorrhagia, post partum bleeding and family history

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40
Q

Haem

What are the causes of abnormal haemostasis?

A

Lack of specific factor -> failure of production (congenital and acquired) or increased consumption/clearance; defective function of a specific factor -> genetic defect, acquired defect (drugs, synthetic defect, inhibition)

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41
Q

Haem

What is primary haemostasis?

A

Formation of unstable platelet plug (adhesion and aggregation)

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42
Q

Haem

What are the disorders of primary haemostasis?

A

Thrombocytopenia (low no. of platelets) in bone marrow failure (leukaemia, B12 deficiency) or accelerated clearance (ITP, DIC); impaired function (hereditary absence of glycoproteins or storage granules, acquired due to drugs (aspirin, NSAIDs, clopidogrel)

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43
Q

Haem

What is autoimmune thrombocytopenic purpura (auto-ITP)?

A

Antiplatelet auto antibodies attack sensitised plateletand attach onto macrophage

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44
Q

Haem

What is the blood coagulation cascade?

A
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45
Q

Haem

What are the mechanisms and causes of thrombocytopenia?

A

Failure of platelet production by megakaryocytes; shortened half life of platelets; increased pooling of platelets in an enlarged spleen and shortened half life

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46
Q

Haem

What factors are not present in the hereditary platelet defects?

A

GpIIb/IIIa, GpIa, dense granules (no ADP)

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47
Q

Haem

What are the names of some hereditary platelet defects?

A

Glanzmann’s thrombasthenia, Bernard Soulier syndrome and storage pool disease

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48
Q

Haem

What von Willebrand Factor disorders exist?

A

VW disease -> hereditary decrease of quantity/function (common), acquired due to antibody (rare)

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49
Q

Haem

What is vW disease?

A

vWF has 2 functions: binding to collagen and capturing platelets and stabilising factor VIII (which may be low if vWF is low); VWD is usually hereditary with deficiency of typ 1/3 of VWF or abnormal function of t2 VWF

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50
Q

Haem

What are the disorders of the vessel wall?

A

Inherited (rare) ->hereditary haemorrhagic telangiectasia, Ehlers-Danlos syndrome and other connective tissue disorders; Acquired -> scurvy, steroid therapy, ageing (senile purpura), vasculitis

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51
Q

Haem

What are the main disorders of primary haemostasis?

A
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52
Q

Haem

What is typical primary haemostasis bleeding?

A

Immediate, Prolonged bleeding from cuts, Epistaxes, Gum bleeding, Menorrhagia , Easy bruising, Prolonged bleeding after trauma or surgery

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53
Q

Haem

What kind of bleeding occurs during thrombocytopenia?

A

Petechiae

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54
Q

Haem

What kind of bleeding occurs during severe VWD?

A

Haemophilia-like bleeding

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55
Q

Haem

How do you test for disorders of primary haemostasis?

A

Platelet count, bleeding time (PFA100 in lab), assays of VWF, clinical observation

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56
Q

Haem

What is secondary haemostasis?

A

Stabilisation of plug with fibrin

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57
Q

Haem

What is the role of coagulation cascade?

A

Generate a burst of thrombin which will convert fibrinogen to fibrin -> which deficiency results in failure of thrombin generation and fibrin formation

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58
Q

Haem

What is haemophilia?

A

Failure to generate fibrin to stabilise platelet plug

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59
Q

Haem

What are hereditary disorders of coagulation where there is deficiency of coagulation factor production?

A

Hereditary: Haemophilia A/B (factor VIII/IX) -> severe but compatible with life, spontaneous joint and muscle bleeding; prothrombin (factor II) is lethal; factor XI causes bleeding after trauma but not spontaneously; factor XII has no excess bleeding at all

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60
Q

Haem

What are acquired disorders of coagulation where there is deficiency of coagulation factor production?

A

Liver disease (failure, which decreases production as most coagulation factors are synthesised in liver), dilution (red cell transfusions don’t contain plasma, but major transfusions require plasma as well as rbc/platelets; anticoagulant drugs (warfarin)

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61
Q

Haem

What are acquired disorders of coagulation where there is increased consumption?

A

Disseminated intravascular coagulation, immmune -> autoantibodies

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62
Q

Haem

What is disseminated intravascular coagulation which causes increased consumption?

A

Generalised activation of coagulation; Tissue factor; Associated with sepsis, major tissue damage, inflammation ; Consumes and depletes coagulation factors; Platelets consumed; Activation of fibrinolysis depletes fibrinogen; Deposition of fibrin in vessels causes organ failure

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63
Q

Haem

How does bleeding differ in coagulation disorders?

A

Superficial cuts do not bleed (platelets), bruising is common, nosebleeds are rare spontaneous bleeding is deep, into muscles and joints, bleeding after trauma may be delayed and is prolonged, frequently restarts after stopping

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64
Q

Haem

What is tthe clincial distinction between bleeding due to platelet vs coagulation defects?

A
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65
Q

Haem

What are the tests for coagulation disorders?

A

Screening tests: prothrombin time, activated partial thromboplastin time, full blood count (platelets); factor assays (factor VIII; test for inhibitors

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66
Q

Haem

Which bleeding disorders are not detected by routine clotting tests?

A
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67
Q

Haem

What disorder of fibrinolysis can cause abnormal bleeding?

A

Hereditary: antiplasmin deficiency; acquired: drugs such as tPA, dissminated intravascular coagulation

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68
Q

Haem

What are the genetics of haemophilia?

A

Sec linked recessive

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69
Q

Haem

What are the genetics of vWD?

A

Autosomal dominant (T2/1), recessive t3

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70
Q

Haem

What are the genetics of all the other factor deficiencies?

A

Autosomal recessive so much less common

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71
Q

Haem

What is the treatment of abnormal haemostasis?

A
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72
Q

Haem

What are the principles of treatment of haemostatic disorders causing bleeding?

A
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73
Q

Haem

What are some additional haemostatic treatments?

A

DDAVP, tranexamic acid, fibrin glue/spray

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74
Q

Haem

What is DDAVP?

A
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75
Q

Haem

What is Tranexamic acid?

A
76
Q

Haem

Where does blood that is transfused come from?

A

Human source as no synthetics yet -> scarce resource as 1 donor gives 1 pint every 4 months (approx.) and they need 9000 units of blood/day in UK

77
Q

Haem

When should blood be used?

A

Balance between risks and benefits, such as when no safer alternative is available -> massive bleeding where plain fluids aren’t enough; if anaemic and iron/b12/folate not appropriate

78
Q

Haem

What is the difference between A, B and O groups?

A

A and B antigens on RBC formed by adding one sugar residue onto common glycoprotein and fucose stem cell on RBC membrane; O has neither A/B sugars, stem only

79
Q

Haem

How are antigens for ABO blood groups determined?

A

By corresponding genes -> A gene codes for enzyme which adds N-acetyl galactosamine to common glycoprotein and fucose stem; B gene codes for enzyme which adds galactose; A and B genes are codominant, O is recessive

80
Q

Haem

How do antigens and antibodies interact in blood groups?

A

Everyone has antbodies against antigens NOT present in own red cells -> naturally occurring IgM is a complete Ab so fully activates complement cascade to cause haemolysis of RBC

81
Q

Haem

What are the different blood groups and how do they react with antigens, antibodies?

A
82
Q

Haem

How do you transfuse blood?

A

Take patient blood sample, do an ABO group test and select donor unit of same group and then cross match (patient’s serum mixed with donor red cells shouldn’t react (agglutinate)

83
Q

Haem

What are RH groups?

A

RhD is most important -> RhD+ or RhD- (no D antigen) -> genes D is Ag present on membrane, d is no Ag and is recessive - 85% of people are RhD+, 15% RhD-

84
Q

Haem

What are the RhD group antibodies and what does it mean to have it?

A

People who are RhD- can make anti-D Ab (IgG) after exposure to RhD -> by transfusion of RhD+ or in pregnancy with RhD+ foetus

85
Q

Haem

What are the implications of anti-D Ab?

A

Future transfusions -> in future must have RhD- blood as otherwise could cause delayed haemolytic transfusion reaction (anaemia, high bilirubin, jaundice); Haemolytic disease of the newborn ->if RhD- has RhD+ foetus, then IgG antibody can cross placenta causing haemolysis of fetal RBC which if severe causes hydrops fetalis and death

86
Q

Haem

What type of RhD should be transfused?

A

Same RhD group blood transfusion (no harm for RhD+ to be given RhD-; O- used in emergency when patient’s blood group not known

87
Q

Haem

What are the other red cell groups and how should these be transfused?

A

Don’t routinely match for all of these groups (C/c/E/e/Kell/Kidd/Duffy) but once Ab formed to one of these Ag then must use corresponding Ag- blood, or risk of delayed haemolytic reaction

88
Q

Haem

How do we prevent incorrect transfusions?

A

Before, test patient’s blood sample for RBC Ab and before transfusing patient as well as testing their ABO and RhD group, must do an Ab screen of their plasma

89
Q

Haem

What are the components of a blood transfusion unit?

A

Collected into bag with anti-coagulant -> not all components given as some components degenerate quickly and is more efficient; red cells concentrated as plasma removed, also avoids fluid overloading patients -> split bag by centrifuging whole bag (red cells bottom, platelets middle, plasma top) then squeeze each layer into staellite bags and cut free (closed system)

90
Q

Haem

How does whole blood split up?

A

x

91
Q

Haem

What is a red cell transfusion made of?

A

Packed cells (fluid removed) - shelf life = 5 wks - stored 4C -> frozen red cells are for rare groups/Ab as there is poor recovery on thawing

92
Q

Haem

How should a red cell transfusion be given?

A

Through a blood giving set to remove clumps and debris

93
Q

Haem

What is FFP?

A

1 unit from 1 donor (300ml) can get small packs for children. Stored at -30C (frozen within 6h of donation to preserve coag factors). Shelf life 2 years. Must thaw approx 20-30 mins before use (if too hot, proteins cook). Give ASAP – ideally within 1h or else coag factors degenerate at room temp

94
Q

Haem

How should FFP be given?

A

Dose 12-15ml/kg = usually 3 units. Need to know blood group - no x-match, just choose same group (as contains ABO antibodies, which could cause a bit of haemolysis

95
Q

Haem

When should FFP be given?

A

1.If bleeding + abnormal coag test results (PT, APTT) -> Monitor response -> clinically and by coag tests 2.Reversal of warfarin (anticoagulant) eg for urgent surgery (if PCC not available) 3.Other conditions occasionally

96
Q

Haem

What is cryoprecipitate?

A

From frozen plasma thawed at 4-8C overnight residue remains; contains fibrinogen and factor VIII -> store at -30C for 2Yrs

97
Q

Haem

What is the standard dose for cryoprecipitate?

A

From 10 donors - 5 in a pack

98
Q

Haem

When is cryoprecipitate used?

A

Massive bleeding and fibrinogen very low and rarely hypofibrinogenaemia

99
Q

Haem

What is the standard dose for platelets?

A

1 pool from 4 donors or 1 donor by apharesis; Need to know blood group but no cross match and can cause RhD sensitisation as some red cell contamination

100
Q

Haem

How are platelets stored?

A

At 22C (room temp) so constantly agitated, shelf life 5 days only (risk of bacterial infection)

101
Q

Haem

When would you give pletelets?

A

Haematology patients with bone marrow failure; massive bleeding or acute DIC; very ow platelets and patient needs surgery; for cardiac bypass and patient on anti-platelet drugs

102
Q

Haem

What is the dose for platelets?

A

1 pool is usually enough -> generally overused in the past, even though it’s a limited resource and cost

103
Q

Haem

What are fractionated products?

A

Large pool -> fractionated like oil; contains Factor VIII and IX and immunoglobulins

104
Q

Haem

When are fractionated products such as Factor VIII and IX given?

A

For haemophilia A and B respectively, factor VIII for vWD, heat treated for viral inactivation, recombinant factor VIII or IX alternatives increasingly used

105
Q

Haem

When are fractionated products such as immunoglobulins given?

A

IM: specific for tetanus, anti-D, rabies; normal globulin as there is a broad mix in popn (HAV); IVIg given pre-op in patients with ITP or AIHA

106
Q

Haem

When do you give 4.5% albumin?

A

Useful in burns, plasma exchanges -. overused as not indicated in malnutrtion

107
Q

Haem

When do you give 20% albumin?

A

When salt is poor, such as for certain severe liver and kidney conditions only

108
Q

Haem

How do we aim to keep blood safe for patient and prevent harm to donors?

A

Keep blood safe by screening for infections and questioning for risk behaviour in donors; preventing harm to donors by questioning them to exclude risky ones (such as those with heart problems)

109
Q

Haem

Which infections are tested for?

A

Hep B (HBsAg, PCR), Hep C (anti-HCV, PCR), HIV (anti-HIV, PCR), HTLV (anti-HTLV), Syphilis (TPHA spirochete), some also tested for CMV (virus) or for HEV

110
Q

Haem

What is an issue with testing for infections in the blood?

A

The window period of infections is not shown as positive so can’t rely on testing -> so need to exclude high risk donors and use voluntary, unpaid donors

111
Q

Haem

How is prion disease (vCJD) screened for and how can it be transmitted?

A

Transmitted via blood transfusion -> plasma is pooled to make fractionated products now obtained from USA; all blood components have white cells filtered out as a precaution as white cells are essential for uptake of vcjd prion into brain to cause disease

112
Q

Haem

What causes sickle cell disease?

A

Single amino acid difference in the bet chain of Hb distinguishes HbA and HbS

113
Q

Haem

Where is sickle cell disease most common?

A

10% of caribbeans and 25% of Africans carry sickle genes

114
Q

Haem

What is betaS?

A

Point mutation at codon 6 of the gene for beta globin -> glutamic acid is replaced by valine

115
Q

Haem

What is the significance of the replacement of the a.a. glutamic acid?

A

Glutamic acid is polar and soluble, valine is non polar and insoluble

116
Q

Haem

What happens to HbS when it become deoxyHbS?

A

Polymerises to form fibres called tactoids which form intertetrameric contacts which stabilises the structure and forms long polymers of HbS within the red cells

117
Q

Haem

What are the stages in red cell sickling?

A

Distortion (polymerisation initially reversible with formation of oxyHbS, which is subsequently irreversible) -> dehydration -> increased adherence to vascular endothelium

118
Q

Haem

What are the different sickle cell disorders?

A

Sickle cell anaemia and compound heterozygous states -> SC, Sbeta thalassaemia; genetically simple but clinically complex with wide range of symptoms affecting the body

119
Q

Haem

What does sickle cell disease encompass?

A

Sickle cell anaemia and all other conditions that can lead to a disease syndrome due to sickling

120
Q

Haem

What symptoms occur due to the shortened life span of sickle red cells?

A

Due to haemolysis anaemia, gallstones and aplastic crisis (parvovirus B19) occurs -> anaemia is partly due to reduced erythropoetic drive as HbS is low affinity hb

121
Q

Haem

Which symptoms occur due to blockage to microvascular circulation (vaso-occlusion)?

A

Due to the distortion of red cells, they become sticky and can cause infarction, tissue damage and necrosis as well as severe pain and loss of function

122
Q

Haem

What are the consequences of a spleen infarction?

A

Hyposplenism (infection) - engorges and acts as reservoir for bodies blood supply so

123
Q

Haem

What are the consequences of an infarction in the bones/joints?

A

Dactylitis, avascular necrosis, osteomyelitis

124
Q

Haem

What are the consequences of a skin infarction?

A

Ucleration

125
Q

Haem

What is dactylitis?

A

Swelling of the finger caused by inflammation which can become painful

126
Q

Haem

What is osteomyelitis?

A

Infection and inflammation of bone and bone marrow

127
Q

Haem

Which lung symptoms are caused by sickle cells?

A

Acute chest syndrome, chronic damage -> pulmonary hypertension

128
Q

Haem

Which urinary tract symptoms are caused by sickle cells?

A

Haematuria (papillary necrosis), impaired concentration of urine (hyposthenuria), renal failure, priapism

129
Q

Haem

What brain symptoms are caused by sickle cells?

A

Stroke, cognitive impairment

130
Q

Haem

What eyes symptoms are caused by sickle cells?

A

Proliferative retinopathy

131
Q

Haem

How does pulmonary hypertension correlate with haemolysis?

A

It correlates with the severity -> due to free plasma Hb resulting from intravascular haemolysis scavenges NO and causes vasoconstriction; associated with increasd mortality

132
Q

Haem

How common is stroke in sickle cell disease?

A

Affects 8% -> most common in 2-9yrs, involving major cerebral vessels

133
Q

Haem

How does sickle cell present?

A

No predictability even within same family -> symptoms rare before 3-6m - switch from fetal to adult Hb synthesis -> early manifestations such as dactylitis, splenic sequestration infection (pneumococcal)

134
Q

Haem

What triggers painful crises in sickle cell disease?

A

Infection, exertion, dehydration, hypoxia, psychological stress

135
Q

Haem

What is the mortality of sickle cell disease?

A

Median survival: F=48y, M=42y; 21% painful crises, 14% chest syndrome, 9% renal failure, 7% infection, 6% perioperative

136
Q

Haem

How do you generally manage sickle cell disease?

A

Folic acid, penicillin, vaccination, monitor spleen size, blood transfusion for acute anaemic events, chest syndrome and stroke, pregnancy care

137
Q

Haem

How do you prevent early mortality in sickle cell disease?

A

Prophylaxis against pneumococcal infection, monitoring for acute splenic sequestration

138
Q

Haem

How do you manage a painful crisis in sickle cell disease?

A

Pain relief (opioids), hydration, keep warm, oxygen if hypoxic, exclude infection (blood and urine cultures), chest X-ray

139
Q

Haem

How do you manage an exchange transfusion in sickle cell disease?

A

Stroke and acute chest syndrome

140
Q

Haem

How do you generally manage haematopoietic stem cell transplantation in sickle cell disease?

A

<16y with severe disease; survival 90-95% and curing 85-90%

141
Q

Haem

How do you manage induction of HbF in sickle cell disease?

A

Hydroxyurea, butyrate

142
Q

Haem

What are the different types of exchange of blood/products that can be used to help manage SCD?

A

Exchange transfusion, haemopoietic stem cell transplantation, induction of HbF

143
Q

Haem

What are the lab features of SCD?

A

Hb low (typically 6-8g/dl), retculocytes high (except in aplastic crisis), film (sickled cells, boat cells, target cells, howell jolly bodies

144
Q

Haem

How do you diagnose sickle cell disease?

A

Solubility test

145
Q

Haem

What is the solubility test and how does it diagnose sickle cell disease?

A

Presence of reducing agent oxyHb converted to deoxy Hb, where solubility decreases, solution becomes turbid; doesn’t differentiate AS from SS

146
Q

Haem

How do you definitively diagnose SCD?

A

Electrophoresis or high performance liquid chromatography separates proteins according to charge

147
Q

Haem

What are the symptoms and presentation of sickle cell trait?

A

HbAS; normal life expectancy and blood count, usually asymptomatic, rarely painless haematuria -> caution with anaesthetic, high altitude and extreme exertion

148
Q

Haem

What are the functions of RBC?

A

Carry O2 from lungs to tissues -> transfer CO2 from tissues to lungs; contain Hb with average of 3.5-5x10^12/L; contain approx. 640million molecules of Hb and have no nucleus/mitochondria

149
Q

Haem

What is Hb?

A

Found in RBC, with MW of 64-64.5 kDa with normal conc in adults = 120-165g/L, contains 3.4mgFe /Hb gram; formed of Haem (synth in mitochondria), globin (synth in ribosomes)

150
Q

Haem

When is Hb synthesised?

A

During development of RBC and begins in pro-erythroblast -> 65% erythroblast stage, 35% reticulocyte stage

151
Q

Haem

How is Hb synthesised?

A
152
Q

Haem

What is the structure of haem?

A

Haem is also present in other proteins (myoglobin, cytochromes, peroxidases, catalases, tryptophan) -> same in all Hb; combination of protoporphyrin ring with central iron atom usually in Fe2+ form -> able to reversibly combine with O2

153
Q

Haem

Where is haem synthesised?

A

In mitochondria which contains ALAS enzyme; regulation occurs

154
Q

Haem

How is haem synthesis regulated?

A

Iron presence (response on receptors from Iron availability); haem has it’s own negative feedback; haem=globiin synthesis

155
Q

Haem

How is globin synthesised?

A

Various types combine with haem to form different Hb -> 8 functional globin chains arranged in 2 clusters -> alpha (alpha and zeta globin genes on short arm of chromosome 16) and beta (beta, gamma, delta and epsilon globin genes on short arm of chromosome 11)

156
Q

Haem

What are the different types of Hb made from (globin chains)?

A

HbF = A2G2 making up 0.5-0.8% of adult Hb; HbA2 = A2D2 makes up 1.5-3.2%; HbA = A2B2 makes up 96-98%

157
Q

Haem

What is the structure of globin?

A

Primary = alpha 141a.a., non-alpha 146a.a.; secondary = 75 alpha and beta chains-helical arrangement; tertiary = approx sphere, hydrophilic surface (charged polar side chains), hydrophobic core, haem pocket (part of molecule where Fe sits in the chain)

158
Q

Haem

What is the difference between oxy and deoxy Hb?

A
159
Q

Haem

How do we show the O2 carrying capacity of Hb?

A

O2-hb dissociation curve -> sigmoid shape (binidng of one molecule facilitates the second molecule binding - cooperativity; P50 is partial pressure of O2 at which Hb is half saturated with O2 = 26.6mmHg)

160
Q

Haem

What shifts the ODC?

A

Left shift= Increased O2 affinity due to decreased 2,3-DPG, increased pH, high CO2 levels - HbF also does this; Right = O2 binds less tightly, increased 2,3-DPG, lower pH, high CO2 - HbS also shifts to right

161
Q

Haem

Which factors affect the position of the ODC?

A

Conc of 2,3-DPG, H+ conc (pH), CO2 in RBC, structure of Hb

162
Q

Haem

What are haemoglobinopathies defined as?

A

Structural variant in Hb or defects in globin chain synthesis (thalassaemia)

163
Q

Haem

How common are thalassaemias?

A

Most common inherited single gene disorder worldwide

164
Q

Haem

How do you classify thalassaemia?

A

Globin type affected and clinical severity (minor trait, intermedia, major)

165
Q

Haem

What is beta thalassaemia?

A

Deletion or mutation in beta globin genes, reduced or absent production of beta globin chains

166
Q

Haem

Where is beta thalassaemia prevalent?

A

Mainly mediterranean countries -> Greece, Cyprus, Southern Italy; Arabian peninsula, Iran, Indian subcontinent, africa, Southern China, South East Asia

167
Q

Haem

How is beta thalassaemia inherited?

A

Recessive; with trait being from mutated beta and normal beta and intermedia from mutated beta and trait mutated beta

168
Q

Haem

How do you diagnose thalassaemia in the lab?

A

FBC (microcytic hypochromic indices; increased RBC relative to Hb); film (target cells, poikilocytosis but no anisocytosis), Hb EPS/HPLC (alpha = normal HbA2 and HbF+/-HbH; beta= raised HbA2 and raised HbF); globin chain synthesis/DNA studies (genetic analysis for beta-thalassaemia mutations and XmnI polymorphism and alpha thal genotype in all cases)

169
Q

Haem

How does beta-thalassaemia trait present and is diagnose?

A

Asymptomatic, slightly raised Hb; hypochromic microcytic cell indices to diagnose

170
Q

Haem

What is thalassaemia major and how does it present?

A

Carry 2 abnormal copies of beta globin gene -> severe anaemia, incompatible with life, without refular blood transfusions with clinical presentation usually after 4-6m of life

171
Q

Haem

What RBC inclusions occur in beta thalassaemia?

A

Alpha chain recipitates and pappenheimer bodies, irregular contracted cells

172
Q

Haem

What is the clinical presentation of thalassaemia major?

A

Severe anaemia usually presenting after 4 months, hepatosplenomegaly, blood film shows gross hypochromia, poikilocytosis and NRBCs; bone marrow (erythroid hyperplasia), extra-medullary haematopoiesis

173
Q

Haem

What are the clinical features of beta-thalassaemia?

A

Chronic fatigue, failure to thrive, jaundice, delay in growth and puberty, skeletal deformity, splenomegaly, iron overload

174
Q

Haem

What are complications of beta-thalassaemia?

A

Cholelithiasis and biliary sepsis, cardiac failure, endocrinopathies, liver failure

175
Q

Haem

How does iron overload occur?

A

Non-trasfusional iron overload: Inefficient erythropoiesis, so iron is not being incorporated into the haem; transfusional iron overload

176
Q

Haem

What are the major causes of death in thalassaemia patients?

A

Cardiac and infections

177
Q

Haem

What are the treatments of thalassaemia major?

A

Regular blood transfusions, iron chelation therapy, splenectomy, supportive medical care, hormone therapy, hydroxyurea to boost HbF, bone marrow transplant

178
Q

Haem

How do transfusions work in thalassaemia?

A

Phenotyped red cells; aiming for pretransfusion Hb 95-100g/L, regular 2-4weekly transfusions -> splenectomy considered if high requirement

179
Q

Haem

How do you manage infection in thalassaemia patients?

A

Yesinia (iron-loving infection), other gram negative sepsis -> prophylaxis in splenectomised patients -> immunisation and antibiotics

180
Q

Haem

What is iron chelation therapy?

A

Start after 10-2 transfusions or when serum ferritin >1000mcg/l -> audiology and ophthalmology screening prior to starting; Desferrioxamine, Deferiprone, Deferasirox

181
Q

Haem

How do you monitor iron overload?

A

Serum ferritin -> >2500 associated with significantly increased complications, acute phase protein, check 3 monthly if transfused, otherwise annually; liver biopsy (rarely performed); T2 cardiac and hepatic MRI -> <20ms increased risk of impaired LF function, check annually or 3-6monthly if cardiac dysfunction

182
Q

Haem

What is HbE?

A

Common variant of hb in south East Asia -> combined with tha can cause severe beta thal major

183
Q

Haem

What is alpha thalassaemia?

A

Deletion or mutation in alpha globin genes, reduced/absent production of alpha globin chains, affects both foetus and adult, excess beta and gamma chain form tetramers of HbH and Hb Barts respectively -> severity depends on number of alpha globin genes affected

184
Q

Haem

What is a thalassaemia carrier?

A

Known as minor/trait -. carry single abnormal copy of the beta globin gene; usually asymptomatic, with mild anaemia

185
Q

Haem

What are the problems associated with treatment of thalassaemia in developing countries?

A

Lack of awareness of problems, lack of experience of health care providers, availability of blood, cost and compliance with iron chelation therapy, availability of and very high cost of bone marrow transplant

186
Q

Haem

How is thalassaemia screened and prevented?

A

Counselling and health education for thalassaemics, family members and general public, extended family screening, pre-marital screening, discourage marriage between relatives, antenatal testing and prenatal diagnosis

Y2 MCD - Haem, Labs, Microbio, Cancer, Immunology (12 decks)

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