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Platelets
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- 4. Origin and structure • Megakaryocytes diameter 35‐160 μm •Platelet diameter 2‐3 μm • Contain an irregular ring of lobed nuclei • Platelets are formed within the cytoplasm of megakaryocytes and released into the circulation • Platelet survival time 8‐12 days • Destroyed mainly in spleen • Blood count: 1.5‐4lakh/ µL of blood
- 5. Morphology • Wet preparations: colourless, moderately refractile, discoid or elliptical • Darkfieldillumination: translucent, sharp contour, few immobile granules • Leishman’s stain shows a faint blue cytoplasm with distinct reddish purple granules • Electron microscopy reveals a cell membrane 6 nm thick which surrounds a cytoplasmic matrix containing Golgi apparatus, endoplasmic reticulum, 50‐100 very dense granules, mitochondria, microvesicles, microtubules, filaments & granules
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- 7. Structure of platelet… • Membrane structures:surface glycoproteins serve as receptors, facilitate platelet adhesion & contraction, and determine expression of specific platelet antigens and antigens shared with other formed elements •Canalicular system:numerous invaginations of the platelet surface and, interspersed among these structures, a set of narrower channels termed the dense tubular system • Dense tubular system : is the major site for storage of Ca2+ and the location of cyclooxygenase • Cytoskeleton • Microtubules • System of contractile proteins • Granules
- 8. Platelet granules • Dense body: ADP, ATP, GTP, GDP, serotonin, secretable Ca++ • Alpha granules: Platelet specific proteins: PF‐4, thromboglobulin, PDGF, thrombospondin Homologs of plasma proteins: fibrinogen, fibronectin, albumin • Dense tubular system: Prostaglandin converting enzymes, contractile calcium • Peroxisomes: Catalase • Lysosomes: Acid hydrolase
- 9. Function • Hemostasis • Blood coagulation •Phagocytosis • Storage & transport of substances
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- 12. Hemostasis (Arrest of bleeding) Formation of hemostatic plug due to Adhesvinessto damaged lining of blood vessels Promoted by Ca++ ions & ADP Aggregation of platelets leads to formation of white bodies or micro thrombi which may grow until they almost fill the lumen of a small vessel At first the aggregation is reversible Then it becomes irreversible, platelet granules are discharged, leukocytes begin to adhere to platelets, fibrin deposition occurs
- 13. Suggested sequence of events in hemostasis • Platelet adherence to collagen in damaged vessels wall • ATP is converted to ADP by ATPase •ADP is released and promotes aggregation of passing platelets : formation of platelet plug • Release of tissue factor from damaged vessels & phospholipids from platelets will promote thrombin formation • Firm clot seals the vessel permanently
- 15. Other reactions in hemostasis • After the initial dilatation the damaged vessels constrict for about 20 minutes, 5‐HT being important in this process • Prostaglandin forming system is also involved in platelet aggregation Arachadonic acid is released from the platelet cell membrane by phospholipase and then rapidly oxidized by the enzyme cyclo oxygenase to PGG2 & PGH2 In the platelets:PGG2 is converted to TX A2 a highly potent platelet aggregator and constrictor of arterial muscle In the arterial endothelium: PGG2 & PGH2 are converted to prostacyclin a potent inhibitor of platelet aggregation and a vasodilator
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- 17. Clot retraction • Clot retraction occurs by shortening of fibrin fibers produced by contraction of attached platelet pseudopodia, which contain actomyosin like protein. •Agents which inhibit cell metabolism or enzyme activity also inhibit clot retraction • Blood allowed to clot in a glass tube at 370 C begins to show clot retraction after 30 minutes
- 18. Phagocytosis • Carbon particles, immune complexes and viruses are phagocytosed by platelets •A vestigial mechanism of clearing particulate material from the blood
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- 20. Non hematological functions of platelets Inflammation Platelets have 4 features common to all inflammatory cells • Posssess wide range of infammatorymediators • Presence of receptors for other inflammatory cells • Ability to respond to noxious stimuli • Cooperative with other inflammatory cells
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- 23. Hemostasis • Physiology of coagulation • Tests for clotting •Clot retraction • Fibrinolysis • Anticoagulants
- 24. Hemostasis (Prevention of blood loss) Mechanisms by which hemostasis is achieved 1.Vascular constriction 2. Platelet plug formation 3. Blood clot formation 4. Clot retraction and fibrinolysis Primary hemostasis Secondary hemostasis Tertiary hemostasis
- 25. Primary hemostasis Vascular phase: Triphasic response 1. Immediate reflex vasoconstriction :An intrinsic response of smooth muscles in small arterioles & pre capillary sphincters 2.Transient vasodilation: Due to PG E2, Histamine & prostacyclin 3. Sustained vascular contraction:Due to release of local autocoid factors from the traumatized tissue and platelets. Ex. TX A2, Fibrinopeptide B, epinephrine , nor epinephrine
- 26. Primary hemostasis… Platelet phase of hemostasis: Important in controlling bleeding from capillaries & small venules in erosion of mucosal surfaces • Adherence to exposed subendothelialstructures & activation • Burst of metabolic activity • Shape change • Platelet aggregation/ plugs • ADP extrusion & other activated subtances • Activation & avalibility of PF 3 & other procoagulants • Initiation of blood clotting • Consolidation of platelet plug by fibrin • Clot retraction
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- 28. Von Willebrand factor • A protein synthesisedby vascular endothelial cells & megakaryocytes • Belongs to a class of adhesive proteins . • Adhesive proteins contain a sequence of amino acids Arg‐Gly‐Asp(RGD) sequence • This sequence allows adhesive proteins to bind to integrins (cell surface proteins) • GP IIb & GP IIIa are two integrins present on platelet surface • Secreted into plasma and also abluminally into the superficial layers of sub endothelium • Sub endothelial vWF contributes to platelet adhesion but is insufficient • After endothelial cell disruption the plasma vWF binds to the subendothelium after which it can bind to surface of unstimulated platelets and link them to the subendothelium
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- 31. Platelet shape change • Occurs within seconds of exposure to activating agents • From flattened discs to spheres with multiple projecting pseudopods •Polymerization of platelet actin • Microtubules that are normally at the periphery go to the center surrounding the granules that have gone to the center prior to release
- 33. Platelet aggregation Defined as the attachment of activated platelets to each other • Primary aggregation: ADP & thrombin cause direct aggregation GP IIb‐IIIa is an integrinthat recoginzes two RGD sequences present on fibrinogen Fibrinogen thus forms a bridge between two opposing activated platelets • Secondary aggregation: substances causing aggregation by release of ADP or PG Thrombospondin from alpha granules leads to ireversible aggregation by binding to fibrinogen & GP IV on platelet surface
- 34. Platelet activation… Series of progressive overlapping events • Shape change • Aggregation •Liberation & oxidation of arachadonic acid • Secretion of alpha & dense granules • Reorganization of surface membrane phospholipids • Oriented centripital contraction of actomyosin
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- 36. • Raised cytosolic Ca++triggers Phosphorylation of myosin light chain kinase. Required for reorientation of cytoskeletal proteins needed for platelet shape change, secretion and contraction Activation of a calcium dependent protease called calpain which through proteolysis activates other platelet enzymes Activation of phospholipase A2
- 37. Prostaglandin thromboxane system Membrane PL AAHPETE HETE Prostacyclin PGG2+ PGH2 PGF2α, PGD2, PGE2 Malonaldihyde TXA2 PLA2 Inhibition of release Aggregation Lipoxygenase GPX Cycloxygenase Aspirin TX synthase Initiation of release Aggregation
- 38. Role of aspirin • Aspirin irreversibly inactivates platelet cycloxygenase • Thus synthesis of PGH2& TX A2 is prevented • Prolongation of bleeding time may occur • Therapeutic role in patients of coronary artery disease
- 39. • PGH2: Acts as a cofactor enhancing collagen’s ability to function as a platelet agonist • TX A2: Binds to a specific platelet membrane receptor with resultant activation of phospholipaseC & amplification of platelet activation through further generation of DAG & IP3 • Prostacyclin: Secreted by endothelium helps to keep platelets in an unstimulated state through activation of platelet adenyl cyclase & a resultant rise in platelet cAMP levels • PGD2: Can also activate platelet adenyl cyclase
- 40. Phosphoinositol metabolism Platelet activation Phosphatidyl inositolbis phosphate(PIP‐2) Diacyl glycerol(DG)+Inositol triphosphate(IP3) Phosphatidic acid(PA) Mobilises Ca ++ from intracellular stores Mobilises Ca ++ from intracellular stores Co factor for Protein kinase C
- 41. Platelet release reaction α granules Platelet proteins Thrombospondin: Palteletaggregation PF4: Neutrlises anticoagulant activity of heparin, competes with antithrombin III for bonding sites on heparan sulphate present on endothelial cells, chemo attractant for WBC, smooth muscle cells & fibroblasts PDGF:chemo attractant for WBC, smooth muscle cells & fibroblasts TGF‐β:chemo attractant for WBC, smooth muscle cells & fibroblasts Analogus of plasma proteins: Albumin, IgG‐ no known hemostatic function Fibrinogen, vWF, Factor V‐ known hemostatic function Dense granules: ADP, ATP, Calcium, serotonin Lysosomal granules:
- 42. Compaction & stabilization of platelet plug • The GP IIb‐IIIa hetrodimertraverses the platelet membrane • When fibrinogen binds to the external domain of GP IIb‐IIIa the cytoplasmic domain is altered and binds to actin filaments • This orients centripetal contraction
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- 44. Blood clotting factors Factor I (Fibrinogen): a soluble plasma protein. In afibrinoginemia clotting does not occur Factor II(Prothrombin): Inactive precursor of thrombin Factor III(Tissue factor/ Tissue thromboplastin): converts prothrombin to thrombin in presence of factors V, VII, X, Ca++and phospholopids Factor IV (Calcium): Essential for clotting. FactorV(Labile factor/ proaccelerin): FactorVII(Stable factor/ proconvertin): Deficiency induced by oral anticoagulants
- 45. Blood clotting factors… • FactorVIII(Antihemophilic globulin/factor A): Congenital defficiencycauses Classical Hemophilia • FactorIX (Christmas factor/ antihemophilic factor B): Congenital deficiency leads to a hemorrhagic state resembling Hemophila(Christmas disease) • Factor X(Stuart‐Prower factor) • Factor XI(Plasma thromboplastin antecedent/ Antihemophilic factor C) • FactorXII(Hageman factor, contact factor) • Factor XIII(fibrin stabilizing factor)
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- 49. Physiology of clotting process Thrombin‐fibrinogen reaction Formation of fibrin clot is the only visible &measurable part of clotting process Type of reaction • Proteolysis Fibrinogen Fibrin monomers + Peptides •Polymerization Fibrin monomers Fibrin polymers (Soluble fibrin clot) • Clotting Fibrin polymers Insoluble fibrin clot Thrombin Factor XII Ca++
- 50. • Conversion of prothrombin to thrombin requires Prothrombinactivator or thromboplastin Prothrombin activator is formed in 2 main ways As result of tissue damage (Extrinsic system) Activation of blood constituents(Intrinsic system) Key reaction: Factor X Factor Xa
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- 53. Extrinsic system… • Key event triggering blood coagulation during hemostasis is exposure of blood to tissue factor •It also acts as a cofactor for activation of factor VII
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- 55. Intrinsic system • More complicated • More prolonged •Fibrinolytic and kinin forming systems are also activated Enzyme cascade hypothesis(Macfarlane): Surface contact induces a sequence of changes in which an inactive precursor is converted into an active enzyme which then acts on the next precursor to form the next active enzyme… An amplifying system
- 56. Intrinsic system… • Factor XII, prekallikrein,Factor XI & High molecular weight kininogenare known as the contact activation factors • Factor XII, prekalikrein & HMWK are essential for triggering blood coagulation in a glass test tube • However they play no role in normal hemostasis since patients with isolated deficiencies of each of these do not bleed abnormally
- 57. • Once Xa is formed clotting occurs within seconds •Contact with a foreign substance i.e. glass or urate crystal produces clotting only after 4‐8 minutes
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- 59. Effects of thrombin • Positive feedback effect on factors concerned with formation of prothrombin activator •Activates factor VIII • Increases activity of factor V & XIII • Promotes aggregation of platelets • Increases the amount of available phosphlipids • After activating these mechanisms soon inactivates them
- 60. Regulation of blood coagulation • Adsorption of thrombin onto fibrin • Neutralization of thrombin by plasma proteinase inhibitors, AntithrombinIII, α2 macroglobulin& heparin cofactor II • Antithrombin III also inhibits the activity of key intermediate enzymes, Factor IXa & Xa • Activated protein C inhibits the cofactors for Factor VIIIa & Va • Extrinsic pathway inhibitor(EPI) & factor Xa neutralize the catalytic activity of Factor VIIa/tissue factor complex
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- 62. Clot retraction • Freshly formed fibrin threads are extremely sticky and adhere to each other, blood cells, tissues & foreign substances • Freshly shed blood sets in a soft jelly –like mass •Gradually it contracts down(retracts) to 40% of its original volume, squeezing out serum • Final clot is more tougher and solid • Clot retraction is impaired if platelets are removed from blood
- 63. Fibrinolysis (Dissolution of clot) Plasminogen Plasmin FibrinSmall peptides (Fibrin degradation products) Intrinsic plasminogen activators get activated by: Body or mental stress, operation, violent exercise, adrenalin injection Extrinsic activators: Widely distributed throughout the cell & body fluids Tissue activators occur in microsomes, urokinase in urine Exrtinsic / Intrinsic Plasminogen activators Plasmin
- 64. Fibrinolytic system & its regulation by protein C Endothelial cells (Thrombomodulin thrombin complex) Protein CActivated protein C +Protein S Inactivates inhibitors of t‐PA Plasminogen Plasmin Lyses fibrin VIII inactive VIIIa V inactive Va Thrombin t‐PA, u‐PA
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- 68. Tests for defects in blood clotting Screening for adequacy of hemostatic plug formation • Platelet count •Bleeding time: for conditions other than thrombocytopenia that can impair the formation of hemostatic plug
- 69. Tests for defects in blood clotting… Screening for the adequacy of blood coagulation • Prothrombin time: Measures the adequacy of reactions that clot plasma when a very high concentration of tissue factor is present. Tests the adequacy of extrinsic system •Activated partial thromboplastin time: Measures the adequacy of clotting reactions that clot plasma when a reagent optimizing the contact activation reactions & providing procoagulant phospholipid is present Tests adequacy of intrinsic system
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- 71. Disorders affecting formation of platelet plug Thrombocytopenia • Physiological: New born, Menstruation • Pathological: Decreased marrow production: Tumours, fibrosis, aplasia, drugs(thiazidediuretics) Spleenic sequestration: Spleenomegaly Increased destruction: Auto antibody formation, aspirin, insecticides, cardiac valves, Sepsis, vasculitis
- 72. Disorders affecting formation of platelet plug… Functional platelet defects Disordered adhesion Von Willebrand’s disease: vWF, Factor VIII activity, BT Most common hereditary hemostaticdisorder Disordered aggregation Thrombasthenia(Glanzmann’s syndrome) Afibrinoginemia Disordered granule release Chediak Higashi syndrome Cardiopulmonary bypass Myeloproliferative disorders Aspirin & other NSAIDS
- 73. • Platelet count • >1 lakh: Asymptomatic, Normal bleeding time •50000‐1 lakh: Bleeding occurs after severe trauma, Bleeding time slightly prolonged • <50000: Easy bruising manifested by skin purpura after minor trauma • <20000: Spontaneous bleeding, usually have petechiae, intracranial/ spontaneous bleeding
- 74. Disorders affecting blood coagulation Hereditary disorders • Factor VIII deficiency(Hemophilia A) • Factor IX defficiency(Hemophilia B) •Factor XI deficiency: Autosomal recessive Acquired disorders • Vitamin K deficiency • Liver disorders: Fall in all factors except factor VIII • Disseminated intravascular coagulation • Acquired antibodies against clotting factors X linked recessive disorders
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- 77. Anticoagulants in vivo • Antithrombin III: Serine protease inhibitor •Heparin • Thrombomodulin: Thrombin binding protein • Thrombomodulin‐thrombin complex: Activates protein C • Activated protein C and S • Plasmin • Dicumarol & Warfarin: Inhibit action of vitamin K
- 78. Anticoagulants in vitro – EDTA – Oxalate –Heparin – Sodium Citrate – Sodium Fluoride/Potassium Oxalate
- 79. Characteristics • It must not alter the size of the red cells • It must not cause hemolysis •It must minimize platelet aggregation • It must minimize disruption of the staining and morphology of leukocytes • It must be readily soluble in blood
- 80. EDTA (Ethylenediaminetetraacetic acid) • Best meets the above requirements, and is used most frequently. •The tripotassium salt (K3EDTA), and the disodium salt (Na2EDTA). • Calcium EDTA is not used as an anticoagulant, but in the treatment of lead poisoning • Mode of action: It forms insoluble calcium salts by chelation • Uses: Making a blood smear for cell morphology studies, test for microfilaria, perform cell counts, BUN, plasma protein, fibrinogen, glucose, determination of Coomb's Test • EDTA preserves the staining and morphological characteristics of leukocytes • Disadvantages Excessive concentrations of EDTA will cause shrinkage of RBC's and erroneous PCV, MCV and MCHC results
- 81. Oxalate • A mixture of dry ammonium oxalate and potassium oxalate in the ratio of 3:2 is used •Mode of action: It combines with calcium to form insoluble Ca oxalate. • Potassium oxalate alone causes red cells to shrink; ammonium oxalate alone causes red cells to swell. Used together, little cellular distortion occurs in the first hour after collection • Uses: The oxalate mixture may be used for hematological sedimentation studies. Potassium oxalate alone is valid for immediate glucose determinations. Ammonium oxalate is used as a diluent in some methods for manually counting WBCs and platelets • Disadvantages – 1) It does not prevent platelet aggregation in vitro as effectively as EDTA. – 2) It is poisonous and should not be used for blood transfusion.
- 82. Heparin • Chemical structure: A polysaccharide derived from glucosamine and glucuronic acid. Contains many sulphategroups. • Molecular weight averages 15000‐18000 • Anticoagulant action due to its strong electronegative charge due its sulphuric acid group • Antagonists: Toludene blue & protamine by antagonizing the negative charge of heparin
- 83. Heparin… • First isolated from Liver • Subsequently demonstrated in extract if many other organs •Inhibits blood coagulation both in vitro & in vivo • Mechanism of action: Prevents activation of prothrombin to thrombin Neutralizes action of thrombin on fibrinogen Facilitates the action of antithrombin III
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- 85. Sodium citrate • Acid citrate dextrose (ACD) is prepared from disodium hydrogen citrate and is the anticoagulant of choice for blood transfusions. used in the ratio of 1 part ACD to 4 parts of blood •Mode of action: It combines with calcium to form an insoluble salt of calcium citrate. • Sodium citrate is the anticoagulant of choice for studies of platelet function and morphology • e. Disadvantages: – 1) It interferes with many chemical tests. – 2) Used alone it preserves blood for only a few hours. – 3) It has a tendency to shrink cells. – 4) Because of a 10% dilution of blood, Na‐citrate is generally not used for CBC.
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- 87. Blood groups • Agglutinogen : The antigen present on RBC surface •Major 0‐A‐B blood types Blood group A: A antigen A present on surface Blood group B: B antigen present on surface Blood group AB: A & B antigen present on surf. Blood group O: No antigen present on surface
- 88. Genetic determination of agglutinogens • Genes that determine the A& B phenotypes are found on chromosome 9p • They are expressed in a mendelianco‐ dominant manner • The gene products are glycosyl transferases, A or B, which confer the enzymatic ability of attaching the specific antigenic carbohydrate groups
- 89. Genetic determination of agglutinogens… • Glycosyl transferaseA directs the formation of antigen A on RBC surface • Glycosyl transferase B directs the formation of antigen B on RBC surface • When A & B transferases are absent then no antigen is present on RBC surface and blood group is said to be O
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- 91. Blood types with their genotypes Genotypes Blood types AgglutinogenAgglutinin OO O ‐ Anti a & Anti b OA or AA A A Anti b OB or BB B B Anti a AB AB A & B ‐
- 92. Relative frequencies of different blood groups Western countries India O 47%32% A 41% 20% B 9% 40% AB 3% 8%
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- 94. Rh system of blood grouping • RBC of rhesus monkey when injected into a rabbit, the rabbit developed antibodies to the rhesus RBC •Further it was discovered that rabbit serum containing anti rhesus antibodies could agglutinate not only rhesus RBC but also human RBC in 85% cases • The RBCs of these humans have on their surface an antigen identical to or similar to rhesus antigen • Thus humans having this antigen were termed as Rh positive
- 95. Rh blood group • Three Rhgenes are present • Rh genes are located on chromosome 1 • Types of Rh antigens/ factor: C, D, E • D is most antigenic • The term Rh positive is generally used to mean that the individual has agglutinogen D • 85% Caucasians are Rh positive • 99% Asians are Rh positive
- 96. Difference between ABO and Rh groups • ABO antigens are present on cells other than RBCs whereas the Rh antigen is not present on any other cell except RBCs •In the ABO system the plasma antibodies responsible for transfusion reaction develop spontaneously whereas in the Rh system antibodies only develop in Rh negative persons when they have been previously sensitized
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- 98. Child’s blood group Child’s genotype Mother’s blood group Possible contribution of mother Possible contribution of father Father might have been Father could not have been A AA AO A or AB B A O A A A or AB A or AB O or B O or B BBB BO B or AB O B O B B B or AB B or AB O or A O or A AB AB AB A B A B B A B A or AB O or A O or B O OO OO A B O O O O A or B or O AB AB
- 99. Rh incompatibility • If a Rhnegative person is transfused with Rh positive blood for the first time: No immediate adverse reaction • If the same individual receives a second transfusion later anti Rh antibodies are synthesized promptly in large amounts
- 100. Rh incompatibility in pregnancy… • Rhnegative female • Rh positive male • Fetus is Rh positive Chances of an apparent abnormality resulting from Rh incompatibility are Negligible in first pregnancy 3% during second pregnancy 10% during third pregnancy
- 101. Rh incompatibility in pregnancy… Erythroblastosis foetalis/ Hemolytic disease of newborn Fetal RBCs undergo massive hemolysis Compensatory increase in erythropoieticactivity leading to immature cells in circulation Enlargement of extramedullary sites of hematopoiesis leads to hepatomegaly & spleenomegaly Child is anemic, Jaundice (Hemolytic) is present, edema Hydrops fetalis: Death in utero Kernicterus: Deposition of unconjugated bilirubin in the basal ganglia If bilirubin > 20 mg % then brain damage
- 102. Erythroblastosis fetalis… Preventive treatment: Giving anti Rh antibodies to Rhnegative pregnant mother Mechanism by which anti Rh antibody prevent the complication of Rh incompatibility They destroy fetal red cells which cross over to the maternal circulation. Thus antigenic stimulus is reduced High antibody levels inhibit production of the same antibody molecules Definitive treatment: Exchange transfusion with Rh negative blood
- 103. Other blood group systems • Lewis system • I System •P system • MNSSU sysetm • Kell system: Immunogenicity is third behind the ABO & Rh systems • Duffy system • Kidd system
- 104. Blood transfusion: Compatibility testing • ABO‐Rh typing: Antibodies are directed against those antigens that lack in the individual’s own blood •Cross matching: A trial transfusion within a test tube in which donor RBC are mixed with recipient serum to detect a potential for serious transfusion • Antibody screen: A trial transfusion between the receipient’s serum & commercially supplied RBC’s that are specifically selected to contain optimal number of RBC antigens
- 105. Storage of blood • CPDA‐1 Citrate : Anticoagulant Phosphate : Buffer Dextrose: energy source Adenine: For resynthesis of ATP so as to extend the storage time from 21 to 35 days AS‐1: (Adsol): Adenine, glucose, mannitol& NaCl Increases shelf life to 42 days AS‐3: (Nutricel): Contains adenine,glucose, citrate, phosphate, NaCl
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- 108. Storage of blood Three problems • Anticoagulation • Preservation of cell viability •Preservation of cell function Criteria for assessing the adequacy of banked blood 70% survival at 24 hours
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- 112. RBC storage lesion… • Decreased DPG • Increased affinity of Hbfor oxygen • Increased Hb but no proportionate increase in oxygen avability
- 113. RBC storage lesion… • Accumulation of lactate • Accumulation of H+ions • Decrease in pH • Loss of K+ and gain of Na+ • Increased osmotic fragility • Some cells undergo lysis
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- 115. • ACD(Acid citrate dextran) Glucose is present RBC storage for 3 weeks • CPD(Citrate phosphate dextran): Modified ACD with added NaH2PO4 Viability after first 24 hours is better At 4oC blood may be stored for 21 days •CPDA‐1: CPD supplemented with adenine and with 25% more glucose than CPD(Standard anticoagulant preservative) RBC storage up to 35 days
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- 117. Indications of blood transfusion • Hypovolemia: Blood loss < 20 % of total blood volume does not require RBC transfusion fluid replacement is sufficient • Surgery •Anemia: Hb levels < 6 gm % require transfusion
- 118. Pre transfusion testing Pre transfusion testing of a potential recipient consists of the following • Forward type: Determines the ABO & Rh phenotype of the recipient •Reverse type: Detects isoagglutinins in the patients serum and should correlate with the forward type testing. The alloantibody screen identifies antibodies directed against other RBC antigens • Cross matching: Donor RBC’s are mixed with recipient plasma on a slide and checked for agglutination
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- 124. Adverse effects of transfusion… • Immune mediated reactions… Graft versus host disease Mediated by donor T lymphocytes that recognize host HLA as foreign and mount an immune response S&S: fever, cutaneous erruptions, diarrhoea& liver abnormalities Clinical manifestations occur 8‐10 days post transfusion
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