Agenda limitations of clinical laboratories to evaluate hypercoagulability and the underlying cause for thrombosis what is the INR the lupus anticoagulant and the antiphospholipid antibody syndrome hassouna 1
Diagnosis of hypercoagulability is by Molecular markers Are products of clotting and fibrinolysis reactions Diagnosis of hypercoagulability is by antibodies raised against molecular markers F1+2 fragment, TAT, FPA, D-dimer, t-pa and thrombomodulin hassouna 2
Fibrinolysis Mechanisms When crosslinked fibrin undergoes fibrinolysis, the peptides joining D- and E- domains are cleaved, leading to fibrin split products. Tetramolecular Branch Point D-tetramer D-trimer Trimolecular Branch Point D-dime r Fibr inolysis Plasmin D-dime r Fibrin tpa Pg E D-trimer DY D-tetramer hassouna 3
Molecular Markers Except for D-dimer molecular markers are not tested in clinical laboratories hassouna 4
Diagnosis of thrombosis By clinical signs and symptoms by radiographic, ultrasound,or magnetic resonance Imaging Laboratory testing is used to diagnose the underlying cause for thrombosis hassouna 5
Underlying cause for Vascular Occlusion is not always thrombosis thrombosis: clots in circulating blood are created by abnormal thrombin activity embolism: dislodged clot or plaque impaired clot lysis: persistence of blood clot in circulating blood hassouna 6
Underlying Mechanism of Vascular Occlusion Clots in circulating blood are created by abnormal thrombin activity hassouna 7
Abnormal thrombin activity DIC acute and chronic surgery, obstetrics, burns infections etc antiphospholipid antibody syndrome hassouna 8
Tissue factor Is not present in circulating blood is encrypted in cell membranes is de-encrypted by injury to cells de-encrypted tissue factor becomes the factor VII receptor factor VII bound to tissue factor initiates clotting reactions hassouna 9
Initiation of clotting reactions TF. TF. FVII FVII complex complex FVII FVII dark dark blue blue soluble soluble TF TF light light blue blue Gla Gla residues residues yellow yellow hassouna 10
Thrombin active site cleft hassouna 11
Schematic Model of Native Fibrinogen Fibrinogen is a symmetric dimeric structure consisting of three pairs of non-identical polypeptide chains Aa, Bb and g. b FPA a g FPB a r PI Fibrinogen fxiii g a hassouna 12 b
Fibrin Assembly: Non-covalent interaction between E- and D-domains This type of fibrin is extremely susceptible to degradation. b IIa a a r PI g Fibrin tpa fxiii g a b D-domain E-domain D-domain hassouna 13
Underlying Mechanism of Vascular Occlusion impaired clot lysis: persistence of blood clot in circulating blood hassouna 14
Impaired clot lysis Decreased plasminogen levels abnormal plasminogen-fibrinogen interactions decreased T-PA activity increased PAI-1 decreased FXII and prekallikrein activities atherosclerosis hassouna 15
Cause for abnormal thrombin activity Decreased potential to inhibit thrombin activity hassouna 16
Acquired and inherited deficiencies antithrombin protein C protein S factor V Leiden G20210A polymorphism is complicated by variable clinical expression in family members with identical genotypes hassouna 17
Antithrombin A representation of the heparin pentasaccharide binding site showing the D-helix (red) and the A-helix (green) and the side chains of the pentasaccharide binding residues (blue) A representation of the heparin pentasaccharide binding site showing the D-helix (green) and the side- chains of the pentasaccharide binding residues (blue) hassouna 18
Biologically active domains in procoagulant factors hassouna 19
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Activity, concentration,gene structure hassouna 21
Agenda Limitations of Clinical tests in the diagnosis of thrombosis hassouna 22
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Clinical assays hassouna 24
Clinical Assays hassouna 25
What is the INR Is it a clotting test is it the time in sec for plasma to clot is it the time in sec for blood to clo hassouna 26
TF. TF. FVII FVII complex complex FVII FVII dark dark blue blue soluble soluble TF TF light light blue blue Gla Gla residues residues yellow yellow hassouna 27
The prothrombin time test (PT) tissue factor from rabbit brain and calcium chloride 200 L are added to plasma 100 L and the time taken for a clot to form is recorded on a photo-optical instrument. The clotting time of the same plasma differs from one equipment to the other hassouna 28
The prothrombin time test Two decades ago, the prothrombin time reagent was prepared with rabbit, ox or human brain thromboplastin. The affinity of rabbit, ox and human thromboplastin for human plasma factor VII in the PT assay varies by as much as 10 sec rabbit: 10-12.9sec human: 23-26sec ox: 17-18.5sec hassouna 29
What is the INR Each thromboplastin reagent receives an International Sensitivity Index or IS I IS I is a value that indicates the affinity of a thromboplastin for human plasma factor VII The prothrombin time ratio or PTR is the clotting time of pooled normal plasma divided by that of the patient plasma. The International Normalized Ratio or INR is a value not a clotting time calculated by raising the PTR to the power of the IS I hassouna 30
INR Limitations The indicated use of the INR is exclusively for patients stabilized on coumadin. The INR is not interchangeable with a clotting time If a patient is not on coumadin the INR is obsolete hassouna 31
Concentrations of Vitamin-K dependent factors mg/l are only slightly decreased with coumadin Prothrombin Protein S Factor X Factor IX Protein C Factor VII 100 21 10 5.9 3.7 0.5 hassouna 32
Factor VII polymorphism hassouna 33
Extrinsic Pathway Extrinsic Rabbit Tissue Factor + Ca Cl2 Human factor VII + + Ca ++ Common hassouna 34
Cause for abnormal thrombin activity A genetic mutation causing increased prothrombin levels in blood results in increased thrombin activity hassouna 35
Activity, concentration and gene structure hassouna 36
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Prothrombin mutation G20210A Prothrombin is a zymogen ( it cannot form a clot, it is the precursor of an enzyme. It is converted to thrombin by initiation of clotting Clotting is initiated by tissue factor tissue factor is encrypted in cells and does not circulate in blood hassouna 39
Thrombin is released from prothrombin by catalytic reactions on negatively charged membrane surfaces hassouna 40
Initiation of clotting reactions TF. TF. FVII FVII complex complex FVII FVII dark dark blue blue soluble soluble TF TF light light blue blue Gla Gla residues residues yellow yellow hassouna 41
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More than one genetic factor may co-segregate with a consequent synergistic effect on thrombotic risk hassouna 43
Lupus Anticoagulant and Antiphospholipid Syndrome hassouna 44
Lupus anticoagulant By definition it is a prolonged clotting time in a lipid based clotting assay The cause for the prolonged clotting time is a substance in the patient s plasma that reacts with the lipids in the reagent and inactivates the lipids in the reagent hassouna 45
Intrinsic Pathway Contact Activator XII XI XIIa XIa IIa IX VIII IXa + VIIIa + PL + Ca ++ Extrinsic hassouna 46 Common
Lupus anticoagulant Cross reacting antibodies against microbial lipid membranes ( most common are antibodies to streptococcus and staphylococcus) cross reacting antibodies against human lipid membranes. Drugs that tie up phospholipids in reagent hassouna 47
Coagulation Analyzer hassouna 48
Intrinsic Pathway Contact Activator XII XI XIIa XIa IIa IX VIII IXa + VIIIa + PL + Ca ++ Extrinsic hassouna 49 Common
Lupus anticoagulant Is not a risk factor for thrombosis indicates a prolonged clotting time that does not correct by mixing the patient plasma with equal volume pooled normal plasma hassouna 50
Membrane Phospholipid Antiphospholipid antibodies are antibodies directed against cell membrane phospholipids hassouna 51
Platelet Membrane Phospholipid Dense Granule Alpha-granule ADP ß-thromboglobulin Platelet factor 4 Platelet-derived Growth Factor Fibrinogen Factor V hassouna 52
Antiprothrombin antibodies Are antibodies directed against prothrombin hassouna 53
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Antiphospholipid antibody syndrome Antiprothrombin antibodies antiphospholipid antibodies anticardiolipin antibodies phospholipid binding protein beta-2- glycoprotein 1 hassouna 55
Antibodies that tie up phospholipid reagents ( lupus anticoagulants) Antiprothrombin antibodies antiphospholipid antibodies anticardiolipin antibodies ( very rare) phospholipid binding protein beta-2- glycoprotein 1 are necessarily a risk factor for thrombosis hassouna 56
Lupus anticoagulant Is not a risk factor for thrombosis indicates a prolonged clotting time that does not correct by mixing the patient plasma with equal volume pooled normal plasma hassouna 57
Intrinsic Pathway Contact Activator XII XIIa XI XIa IIa IX VIII IXa + VIIIa + PL + Ca ++ Extrinsic hassouna Common 58
Extrinsic Pathway Contact Activator XII XIIa TF Extrinsic XI IX VIII XIa IXa + VIIIa + PL + Ca ++ Intrinsic VII VIIa + TF + Ca ++ hassouna 59 Common
If a lab reports a lupus anticoagulant, what next Ask for an antiphospholipid antibody test ask for a prothrombin antibody test ask for an anticardiolipin test if positive, the diagnosis is antiphospholipid syndrome, hassouna 60
Lupus Anticoagulant and Antiphospholipid Syndrome hassouna 61
Antiphospholipid antibody syndrome Must include lupus anticoagulant plus antibodies against prothrombin or phospholipids or cardiolipin antiphospholipid syndrome is diagnosed by clotting assays and by antibody based assays prolonged clotting time without positive antibodies is not a risk factor for thrombosis, miscarriage etc hassouna 62