Ongoing mouthwashes and good oral hygiene. \200 Antiemetics PRN. Follow-up \200 Monitor closely for fi rst 100d (twice-weekly blood tests and weekly clini cal review) for engraftment, transfusion requirements, GvHD, CMV, opportunistic infection, side eff ects of therapy, chimerism, psychosocial needs and relapse. Review 4 \200\2238 weekly for 1st year after 100d if uncomplicated. \200 Review intervals may be extended after 1st year if uncomplicated. 453 Chapter 10 Haemostasis and thrombosis Assessing haemostasis 454 The coagulation system 456 Laboratory tests 458 Platelets 462 Ble eding 466 Bleeding: laboratory investigations 469 Bleeding: therapeutic products 470 von Wi llebrand disease 472 Hemophilia A and B 476 Rare congenital coagulation disorders 482 Conge nital thrombocytopenias 485 Congenital platelet function defects 486 Congenital vascular di sorders 487 Haemorrhagic disease of the newborn 488 Thrombocytopenia (acquired) 490 Specifi c thrombocytopenic syndromes 492 Disseminated intravascular coagulation 494 Liver disease 496 Renal disease 498 Acquired anticoagulants and inhibitors 499 Treatment of spontaneous F VIII inhibitor 500 Acquired disorders of platelet function 502 Henoch \200\223Sch nlein pu rpura 504 Perioperative bleeding and massive blood loss 506 Massive blood loss 508 Heparin 510 Heparin induced thrombocytopenia/with thrombosis (HIT/T) 512 Oral anticoagulant therapy (warfarin, VKAs) 514 New oral anticoagulant drugs 516 Thrombosis 518 Risk assessment and thromboprophylaxis 524 Example of VTE risk assessment 528 Heritabl e thrombophilia 530 Acquired thrombophilia 534 Thrombotic thrombocytopenic purpura (TTP) 53 8 Haemolytic uraemic syndrome (HUS) 540 Heparin-induced thrombocytopenia (HIT) 542 454 CHAPTER 10 Haemostasis and thrombosis Assessing haemostasis Haemostatic capacity is assessed by: \200 History. \200 Examination. \200 Laboratory investigations. Hemophilia Describes a tendency to bleeding and may be heritable (often congenital) or acqu ired. Acquired hemophilia due to anticoagulant drugs is very common in the UK as 1 in 100 o f the population is receiving oral antico- agulant therapy with warfarin. Thrombophilia Describes a tendency to thrombosis and may be heritable (but usually late ons et in adult) or acquired. Acquired thrombophilia is common in hospitalized patients by virt ue of immobility, surgery, and multiple medical illness (VTE including DVT and PE). The haemostatic system maintains the integrity of the vasculature through a complex network of cellular, ligand-receptor, and enzymatic interactions. It is essential that blood remai ns fl uid within the circulation but clots at sites of vascular injury. This is achieved by the equilibrium between: \200 Procoagulant and anticoagulant systems. \200 Fibrinolyti c and antifi brinolytic systems. In response to endothelial damage there is rapid thrombin generation and antifi brinolysis at the site of injury. At adjacent areas of healthy intact endothelium there is enhanced na tural anticoagulant activity and fi brinolytic activity to limit the clot to the site of in jury and thus prevent thrombosis (a blood clot within the lumen of a blood vessel). Regulat ion of the haemostatic network in such a way results in localized clot forma- tion with min imal loss of vascular patency. Pathological disruption of the network results in thrombosis or bleeding, or both; the most extreme example of haemostatic pathology is a complete brea kdown as occurs in disseminated intravascular coagulation (DIC). 455 ASSESSING HAEMOSTASIS 456 CHAPTER 10 Haemostasis and thrombosis The coagulation system The initiation of coagulation is triggered by tissue factor, a cell mem- brane protein which binds activated factor VII (factor VIla). Although there is a smal l fraction of circulating factor VII in the activated state it has little or no enzymatic a ctivity until it is bound to tissue factor. Once bound to tissue factor, factor VIla activates factor IX and factor X (to IXa and Xa re spectively) leading to thrombin generation and clot formation (Fig. 10.1). Thrombin converts soluble fi brinogen into insoluble fi brin monomers which spontaneously p olymerize to form the fi brin mesh that is then sta- bilized and crosslinked by activated f actor XIII (factor XIlla). Further reading Baglin, T. (2005). The measurement and application of thrombin generation. Brit J Haem, 130, 653 \200\22361. Hoff man, M. and Monroe, D.M. (2001). A cell-based model of hemostasis. Thromb Haemostasis, 85, 958 \200\22365. Monroe, D. M. and M. Hoff man (2006) . What does it take to make the perfect clot? Arteriosclerosis Thrombosis and Vascular Biol ogy, 26, 41 \200\2238. 457 THE COAGULATION SYSTEM TISSUE FACTOR XI XIa TISSUE FACTOR: VIIa IXa IX VIIIa Xa X Va prothrombin thrombin (a) fibrinogen fibrin TISSUE FACTOR TISSUE FACTOR: VIIa XI XIa IX IXa VIIIa X Xa Va prothrombin thrombin (b) fibrinogen fibrin TISSUE FACTOR TISSUE FACTOR: VIIa XIa XI IXa IX VIIIa X Xa Va prothrombin thrombin (c) fibrinogen fibrin Fig. 10.1 Thrombin generating mechanism. The thrombin explosion occurs in 3 phases, the fi rst (Fig.10.1a: initiation) in which TF:VIIa generates small amounts of thrombin which enha nces platelet activation (in conjunction with exposed subendothelial collagen at the site o f vascular injury) and V and VIII to their active forms. The activation of Va and VIIIa ope ns the factor IX-dependent pathway to thrombin generation (Fig. 10.1b: amplifi cation) and increasing concentrations of thrombin then lead to back activation of factor XI (Fig. 10.1c : propagation). The activated forms of factors V and VIII are non- enzymatic cofactors whic h assemble and orientate the enzymes (IXa and Xa) on the negatively charged surface of acti vated platelets. 458 CHAPTER 10 Haemostasis and thrombosis Laboratory tests \200 Prothrombin time (PT). \200 Activated partial thromboplastin time (APTT). \200 Fibrinogen (Fgn) level. \200 Thrombin time (TT). \200 Reptilase time (R T). \200 Factor assays. \200 Mixing studies. \200 Thromboelastography (TEG). \200 T ests of fi brinolysis. Coagulation tests are typically performed on plasma that has been sepa- rated from a blood sample by centrifugation. Thrombin generation takes place on phospholipid surfaces (provide d by platelets normally) and so an artifi cial lipid preparation is added as the platelets are removed by the cen- trifugation. Most routine clotting tests use the time taken for a c lot to appear as the endpoint of the assay. Blood is usually taken into tubes containing ci trate, which chelates Ca2+ and thereby prevents clotting. Blood is centri- fuged and the pl asma is removed and recalcifi ed during the clotting assay. PT The PT is the time in seconds for a blood sample to clot after recalcifi - cation and ad dition of thromboplastin (a preparation of tissue factor which is the protein that binds to factor VIIa and initiates thrombin gen- eration). The normal PT is about 11 \200\22314sec, depending on the type of thromboplastin used. The PT is prolonged by: \200 Oral anticoagulant therapy with a VKA (Vitamin K antagonist such as warfarin). Vitamin K defi ciency. \200 Liver disease. \200 DIC. \200 Factor VII defi ciency (con genital isolated VII defi ciency is rare). APTT The APTT is the time taken in seconds for a citrated blood sample to clot after recalc ifi cation and addition of a contact factor activator, such as kaolin. The normal APTT is about 32 \200\22338sec, depending on the type of contact factor activato r used. The APTT is prolonged by: \200 Unfractionated heparin (LMWH has minimal eff ect at therap eutic levels). \200 Oral anticoagulant therapy with a VKA (mildly, the PT is much more sensitive). Vitamin K defi ciency (mildly, the PT is much more sensitive). \200 Liver disease (mildly , the PT is much more sensitive). \200 DIC. \200 Dilutional coagulopathy (massive blood transfusion). \200 Severe and moderate defi ciencies of factors VIII, IX, or XI. \200 Antiphospholipid antibodies (known as lupus anticoagulant activity). \200 Contact factor defi ciency (including factor XII and prekallikrein). 459 LABORATORY TESTS Fgn level Fgn levels are low in: \200 DIC. \200 Dilutional coagulopathy (massive blood transfusion). \200 Advanced liver disease. \200 Following thrombolytic therapy. \200 Congenital hypofi brinogenaemia (very rare). \200 Acquired dysfi brinogenaemias. TT The TT (thrombin time) is the time in seconds for a citrated blood sample to clot after addition of thrombin. The TT is prolonged by: \200 Unfractionated heparin. \200 Hypofi brinogenaemia (E see R are congenital coagulation disorders, p.482 for low Fgn levels) Fibrin degradation products (high levels may occur in DIC and after thrombolysis). RT The RT(reptilase time) is a snake venom-based test. It is prolonged by low Fgn levels bu t not by heparin and so comparison of the TT and RT is useful for determining if a prolonge d APTT is due to heparin (long TT with n RT = heparin). Factor assays Individual factor assays are useful in patients with a bleeding history and a re guided by PT and APTT results. The cascade model of coagula- tion (Fig. 10.2) is no long er considered to represent the physiological process involved in coagulation. The cascade m odel was derived from observation of results using the PT and APTT assays which are not \200\230physiological \200\231 tests. Therefore, whilst the cascade model may not be \200 \230physiologically true \200\231 it is still a useful framework for interpreting PT and AP TT results. For example, in a patient with a bleeding history with a n PT and a long APTT ( not due to heparin or a lupus anticoagulant) there may be defi ciency of factor VIII, IX, o r XI. Mixing studies If the PT or APTT are prolonged then mixing with n plasma and repeating the test will indicate if the prolongation is likely due to a factor defi ciency (the mix corre cts the abnormality) or an inhibitor such as heparin or a specifi c factor inhibitor (the m ix does not correct the abnormality). Thromboelastography This test measures the physical strength of a clot as it forms. Its rol e in clinical practice is limited. It is often used as a near-patient testing device during surgical procedures with potentially massive blood loss (such as liver transplantation) wh en it is used to guide transfusion therapy. It is useful for identifying severe hyperfi bri nolysis, as occurs during liver transplantation \200\224an indication for using an antiplas min drug such as tranexamic acid. 460 CHAPTER 10 Haemostasis and thrombosis Tests of \201 brinolysis These tests are not performed routinely. Defects of fi brinolysi s have not been linked with a predisposition to thrombosis and bleeding dis- orders due to defective regulation of fi brinolysis being exceptionally rare. The fi brinolytic system ma y have a 1 role in clearing clot as part of wound healing rather than in the immediate ha emostatic response to injury. Nevertheless pharmacological doses of fi brinolytic activator s (e.g. recombinant tissue factor activator) have a very useful clinical role in rapidly ly sing a newly formed clot \200\224 \200\230clot-busting drugs \200\231. Practical application of coagulation tests Clotting tests are indicated in patients with a personal or family history of bleeding. They are not generally indicated as routine preoper a- tive screening tests as they have very low sensitivity and specifi city for surgical ble eding in unselected patients. Preoperative assessment of bleeding risk is better determined by identifi cation of a personal or family bleeding history, which should then be investig ated accordingly. 461 LABORATORY TESTS APTT intrinsic pathway extrinsic pathway CONTACT FACTOR XII XIIa XI XIa PT TISSUE FACTOR VIIa VII IX IXa VIIIa X Xa Va common pathway prothrombin thrombin fibrinogen fibrin Fig. 10.2 Cascade model of coagulation. The concept of the cascade model involves an extrin sic pathway (triggered by tissue factor and measured by the PT) and an intrinsic pathway (t riggered by contact factor activation and measured by the APTT) joining in a common pathway (measured by both PT and APTT). The utility of this concept involves comparing the results of the PT and APTT to determine where there is a defi - ciency in the cascade, e.g. a n PT with a prolonged APTT indicates a defect in the intrinsic pathway before it joins the comm on pathway, e.g. a defi ciency of factor VIII. 462 CHAPTER 10 Haemostasis and thrombosis Platelets n platelet survival 7 \200\22310d. Platelets are activated by multiple agonists t hrough numerous intracellular 2nd-messenger pathways. The activation pathways converge on a ctivation of the fi brinogen receptor, glycopro- tein llb-llla (integrin IIb 3), such th at an induced conformational change results in fi brinogen/fi brin binding (see Fig. 10.3). As a result of occupation of the Fgn receptor (GPIIb-IIIa) \200\230outside-in signaling \200\231 consolidates the platelet activation process by upregulating 2nd-messenger pathway s and hence providing a +ve feedback loop. In addition to adhe- sion and aggregation at sit es of vascular injury a major role of platelets in coagulation is the provision of an anion ic phospholipid surface required for assembly of the coagulation factor enzymes and cofacto rs required for thrombin generation. Following vascular injury platelets adhere to subendothelial collagen via the von Willebran d factor (vWF) ligand. Platelets then aggregate to form a platelet mass at the site of inju ry. Laboratory tests Blood collection needs to be with a non-traumatic venepuncture, rapid tran sportation to the lab with storage at room temperature, and testing within a limited time. \200 Platelet count and platelet size. \200 Blood fi lm for platelet morphology. \200 Platelet function at high shear rate (PFA-100). \200 Platelet function at low shear rate (platelet aggregation). \200 Platelet granules and nucleotide quantifi cation. \200 Bl eeding time is no longer recommended as a routine test.1 Platelet count \200 Normal range 150 \200\223450 \227 109/L. \200 Beware pseudothrombo cytopenia \200\224due to platelet clumping typically in EDTA (1% of blood counts) \200\224check fi lm for clumps and if suspicious rep eat count on citrated or heparinized sample. Adequate function is maintained until platelet count <80 \227 109/L. \200 With platelet count <20 \227 109/L there is often easy bruising and petechial hemorrhages and more serio us bleeding can occur. The degree of bleeding is infl uenced by the cause of the thrombocytopenia \200\224more bleeding with marrow failure syndromes (aplastic anemia and p ost-chemotherapy) \200\224less bleeding with peripheral platelet destruction, as in immune thrombocytopenic purpura (ITP). Reference 1. Harrison, P. (2005). Platelet function analysis. Blood Rev, 19, 111 \200\22323 . 463 PLATELETS ADP collagen thromboxane thrombin adrenaline thromboxane synthesis G-coupled proteins ADP GPIIbIIIa Fig. 10.3 Mechanisms of platelet activation. Platelets are activated by multiple agonists t hrough numerous intracellular 2nd- messenger pathways. The activation pathways converge on activation of the fi brinogen receptor, glycoprotein IIb-IIIa, such that an induced conform ational change results in fi brinogen/fi brin binding. Platelet activation is completed by occupation of the fi brinogen receptor resulting in \200\230outside-in signaling \200\231 and upreg- ulation of 2nd-messenger pathways. 464 CHAPTER 10 Haemostasis and thrombosis Platelet size Large platelets are often biochemically more active; high mean platelet volum e (MPV >10fL) is associated with less bleeding in patients with severe thrombocytopenia, ac quired BM disorders are a less likely cause of thrombocytopenia the higher the MPV (especia lly MPV >10fL). Reticulated platelets can be counted by some new blood count ana- lysers and may prove to b e useful in assessing thrombocytopenia (often reported as \200\230immature platelet fracti on \200\231 (IPF). Altered platelet size is seen in inherited platelet disorders \200 High MPV (>10fL) in Ma y \200\223Hegglin anomaly, gray platelet syndrome. \200 Low MPV (<7fL) in Wiskott \200 \223Aldrich syndrome (WAS), X-linked thrombocytopenia. Morphology Pseudothrombocytopenia may be due to in vitro platelet clumping and clumps may b e visible in blood fi lm. Platelet morphology may be abnormal and white cells may contain i nclusions in some inherited thrombocytopenias, e.g. May \200\223Hegglin anomaly. Platelet function at high shear rate (PFA-100) Automated technique that measures the abilit y of platelets to occlude an aperture at high shear rate. Minimal sample manipulation. Test performed on citrated blood sample within 4h of sample collection. Abnormal in VWD and pla telet function defects. Platelet function at low shear rate (platelet aggregation) Performed on platelet-rich plasm a prepared by slow centrifugation of cit- rated blood sample. Performed within 4h of sample collection. Poor cor- relation with bleeding tendency except in specifi c congenital disor ders with severe platelet function abnormality, e.g. Glanzmann thrombasthenia (GT), Bernard \200\223Soulier syndrome (BSS). \200 Agonists used for aggregation studies include ADP, collagen, arachidonic acid, adrenaline (epinephrine). Response to ristocetin is an agglutination response dependent on induced conformational cha nge of platelet membrane proteins, e.g. glycoprotein Ib-IX-V, promoting interaction with vW F. Ristocetin-induced platelet agglutination (RIPA) is carried out at high (1.2mg/mL) and low ristocetin concentrations (0.5mg/dL). +ve RIPA at 0.5mg/dL is an abnorma l result and is observed in type 2B VWD and with very high vWF levels, e.g. pregnancy. Platelet granules and nucleotides Platelet storage pool disorders (SPD) are characterized b y absent platelet granules. granule proteins include -thromboglobulin ( -TG) and plat elet factor 4 (PF4) which can be measured by ELISA \200\224defi cient in -granule storage pool defects. Nucleotides (ADP/ATP) can be measured by a variety of techniques including H PLC and are defi cient in dense granule -storage pool disorders. These are beyond the sco pe of the routine laboratory. 465 PLATELETS Clinical utility of platelet function tests Main role is in diagnosis of inherited platelet functional defects. In acquired platelet dysfunction 2 to drugs (aspirin, clopidogrel), and disorders such as renal and hepatic disease, DIC, platelet function is rarely tested as the clinical utility is not established in this setting, i.e. no established correlation b etween test results and bleeding tendency. Therefore, platelet function testing is generall y restricted for the investi- gation of possible congenital bleeding disorders. Drugs impair platelet function Many drugs impair platelet function, e.g. aspirin, clopidogr el, dipyrida- mole, glycoprotein IIb/IIIa inhibitors such as abciximab, and NSAIDs. Many ot her drugs have subtle eff ects on platelet function that are rarely of clinical importance. Drug-induced thrombocytopenia is a more common and clinically important drug eff ect. 466 CHAPTER 10 Haemostasis and thrombosis Bleeding Major issues to be determined \200 Is haemostatic capacity reduced or is there a non-hema tological cause for bleeding? If haemostatic capacity is reduced is it due to a heritable defect with late clinical onset or is it the result of a newly acquired defect? If newly acquired is it due to an anticoagulant drug? \200 If not due to reduced haemosta tic capacity then what are the likely circumstances that resulted in abnormal bleeding? Causes of bleeding Surgery, trauma, non-accidental injury, coagulation disorders (including anticoagulant drugs), platelet dysfunction (including drug induced, e.g. aspirin), vascula r disorders. Clinical features Is there a lifelong bleeding history, has the patient been previously cha llenged by surgery or dental extraction, is this an isolated symptom? Type of bleeding prob lem that led to presentation, e.g. mucocutaneous, easy bruising, spon- taneous, post-trauma tic. Duration and time of onset. Menstrual history is important \200\224menorrhagia has a l ow +ve predictive value for a bleeding dis- order but absence of menorrhagia has a high \210\222ve predictive value. Absence of obstetric bleeding does not exclude a bleeding diso rder as haemostatic capacity increases signifi cantly in pregnancy. \200 Systemic enquiry : do symptoms suggest a systemic disorder, BM failure, infection, liver disease, renal disease? Past medical history: previous episode, previous known disorder, e.g. ITP, exposure to trau ma, surgery, dental extraction, or pregnancies? Family history: similar bleeding tendency in other family members? Pattern of inheritance \200\224autosomal dominant, sex-linked? Drugs: thrombocytopenia (E Thrombocytopenia (acquired), p.490), platelet dysfunction (E Acquired disorders of platelet function, p.502), cause not always o bvious \200\224aspirin, warfarin? Drug reaction \200\224 allergic purpura. Physical examination: signs of systemic disease \200\224anemia, lymphadenopathy hepato-splenomegaly? Assess bleeding site \200\224check palate and fundi . Check size, e.g. petechiae (pinhead); purpura (larger = 1cm); bruises (ecchymoses) >1cm \200\224 measure them. Joints \200\224swelling or other signs of chronic arthritis, joint d estruction, or muscle contractures from previous bleeds? Vascular lesions: purpura, e.g. allergic purpura, Henoch \200\223Sch nlein pupura (E Henoc h \200\223Sch nlein purpura, p.504), senile purpura, steroid-related, hypergammaglobulinae mic purpura, hereditary haemorrhagic telangiectasia (HHT) \200\224capillary dilatations whi ch blanche on pressure, vasculitic lesions, autoimmune disorders, hyper- sensitivity reacti ons. Preoperative history: is an important aspect of identifying clinically signifi cant bleedin g risk. If abnormal bleeding does occur during operation then exclude surgical bleeding and take blood for testing. Results may not be reliable in immediate postoperative period due to 467 BLEEDING eff ect of blood products and stress response of surgery (high vWF, factor VIIIC and Fgn). Full investigation several weeks after surgery is recommended. The most common cause of an acquired bleeding disorder is anticoagulant therapy (E see Anticoagulant drug therapy, p.514). Antiplatelet drugs Individual response to antiplatelet therapy is extremely variable and ev en aspirin or clopidogrel will produce a signifi cant bleeding tendency in some patients. Treatment: stop antiplatelet therapy. Platelet transfusion for acute severe bleeding. Anticoagulants Approximately 1 in 100 of the population of some countries are now receiving long-term oral anticoagulant therapy with a VKA and overantico- agulation \200\224often du e to intercurrent illness and antibiotic use \200\224is probably responsible for the majori ty of life-threatening bleeds due to antithrombot- ic therapy with VKA. New oral anticoagul ant drugs (NOACs) which are oral direct inhibitors of thrombin and factor Xa are now approv ed as anticoagu- lant drugs. The fi rst 3 drugs to complete phase III clinical trials are d abigatran etexilate, rivaroxaban, and apixaban which are given at fi xed dose and do not re quire monitoring. Increasingly these drugs will be taken by patients and may contribute to or be the cause of bleeding. Surgical bleeding Essential to examine the drug and infusion charts and check that the dose of any drug that may aff ect haemostasis is correct. Determine if the site of surgery is t he only site of bleeding. If this is the case, e.g. there is no bleeding from venepuncture sites or an endotracheal tube and there is no history of previous abnormal bleeding, then d epending on the results of coagulation tests it is important to keep the possibility of ana tomical sur- gical bleeding as a likely possibility. In some cases of severe bleeding the p atient may have to return to theater to look for a bleeding point. Critically ill patients Many potential acquired disorders of haemostasis in critically ill patients. A coagulopathy due to vitamin K defi ciency occurs within a few days in criticall y ill patients with no oral intake. Treatment: IV vitamin K should be used routinely to prevent bleeding. Many critically ill p atients develop disseminated intravascular coagulation (DIC). Disseminated intravascular coagulation (E see Disseminated intravascular coagulation, p.494 .) Major manifes- tations of DIC are end-organ damage due to microvascular thrombosis but t he most readily apparent clinical manifestation is often bleeding due to the consumptive co agulopathy. DIC is a clinical diagnosis supported by the results of laboratory investigatio ns. 468 CHAPTER 10 Haemostasis and thrombosis Treatment: most important aspect of treatment is treating the underlying cause, e.g. sepsis or obstetric emergency such as placental abruption. FFP and platelet concentrates are used to treat bleeding or prevent hemorrhage associated with planned invasive procedures. Massive transfusion Dilutional coagulopathy resulting in defi ciency of clotting factors an d platelets will cause abnormal bleeding in patients receiving large amounts of plasma expa nders and RBCs even in the absence of DIC. Treatment: give replacement therapy with FFP and platelet concentrates guided by repeated m easurement of the PT, APTT, and platelet count. Thrombocytopenia Many drugs result in a reversible idiosyncratic thrombocytopenia. In most cases drug-induced thrombocytopenia is mild and does not cause bleeding. Notable exceptions are quinine and gold-induced thrombocy- topenia which are severe. Evaluation of drug histo ry and cessation of possibly implicated drugs is essential in patients with acquired bleedi ng who are found to be thrombocytopenic. Cytotoxic drugs produce a dose-dependent suppressi on of BM platelet production and thrombo- cytopenic bleeding is common in oncology practice . BM suppression and BM failure syndromes, such as aplastic anemia and myelodysplasia, ofte n result in production of dysfunctional platelets and the bleeding tendency is signifi cant ly greater than in patients with thrombocytopenia and an uncompromised marrow, such as occu rs in ITP. Acquired inhibitors Rare and most often autoantibodies. Platelet autoantibodies result in s hortened platelet survival and thrombocytopenia (immune throm- bocytopenic purpura (ITP)). The bleeding manifestations of ITP are variable and often mild, as compared with thrombocyt openia associ- ated with inadequate platelet production (E see Thrombocytopenia (acquired), an autoantibody to a specifi c clotting factor VIII, produces a severe acquired bleeding d isorder. p.490). Treatment-immunosuppression. Rarely, factor, such as Treatment: consult hematologist. 469 BLEEDING: LABORATORY INVESTIGATIONS Bleeding: laboratory investigations \200 FBC (platelet count). \200 Blood fi lm examina tion. \200 PT, APTT. \200 ESR. \200 Biochemistry \200\224creatinine, LFTs, and immuno globulins. \200 Factor assays and platelet function tests depending on type of bleeding. When PT or APTT abnormal investigate accordingly (E see Laboratory tests, p.458). Testing s trategy depends on history as n PT and APTT do not exclude moderate factor defi ciency suff i cient to cause abnormal bleeding tendency. LMWH, VWD, platelet abnormality, or very rare factor defi ciency such as factor XIII. VWD often missed because PT and APTT and platelet c ount are n. If history suggestive of VWD then plasma level of vWF must be measured. The ble eding time is not a reli- able test and is rarely performed. Fill blood sample tube to the mark to ensure correct anticoagulant concentration. Repeat test if result abnormal. Check p atient not on anticoagulants. Family studies should be considered dependent on history. Further investigations \200 Check blood fi lm for red cell fragments, platelet morphology , TT and RT (if abnormal APTT checking for heparin eff ect), Fgn, fi brin degradation produ cts \200\224XDPs/D-dimer. Vitamin K defi ciency: give vitamin K and repeat 24h later, consider checking II, VII, IX, or X level (vitamin K-dependent) and comparing with factor XI or V (n ot vitamin K-dependent). Liver disease: check LFTs; will not correct to n with vitamin K but may improve due to associated vitamin K defi ciency. Isolated factor defi ciency: assay as indicated by PT/APTT results. \200 Inhibitor: lupus anticoagulant tests, check anticardiolipin antibodies, other factor-specifi c assays. Heparin: abnormal APTT (i APTT ratio), PT n if heparin with APTT ratio <2.5. Prolonged TT with n RT indicates heparin eff ect. \200 Warfarin: PT prol ongation > than APTT, low vitamin K-dependent factors. VWD: diagnosis of VWD requires measurement of vWF level and function. 470 CHAPTER 10 Haemostasis and thrombosis Bleeding: therapeutic products Fresh frozen plasma (FFP) Dose is 10 \200\22320mL/kg. Solvent-detergent virally-inactivated FFP is now produced and is used for rare bleeding disorders and patients with TTP who will require repeated exposure to FFP. Methylene blue-treated single donor unit FFP is also ava ilable as a virally-inactivated product. Platelet transfusion Typically used for thrombocytopenic bleeding, rarely required for abno rmality of platelet function. Desmopressin A vasopressin analog that increases the plasma levels of FVIII and vWF (mainly by release from stores) and directly activates platelets. Desmopressin is usually given su bcutaneously or intravenously but the SC route reduces the severity of side eff ects of hea dache, fl ushing, and tachycardia. Tachyphylaxis (a progressively diminished response) can occur. Water retention and hyponatraemia may complicate therapy and for this reason it shou ld not be used in very young children. Fluid intake should not exceed 1L in the 24h followi ng treatment and with repeated doses the serum sodium should be monitored. Desmopressin wil l also shorten the bleeding time in patients with renal or liver failure. Tranexamic acid Inhibits the binding of plasminogen and t-PA to fi brin and eff ectively bl ocks conversion of plasminogen to plasmin \200\224fi brinolysis is thus retarded. Used for menorrhagia and after prostatic surgery. Tranexamic acid may also reduce bleeding in VWD an d FVIII defi ciency after dental extraction where it is normally used in combination with d esmopressin or clotting factor concentrate. May be of value in thrombocytopenia (idiopathic or following cytotoxic chemotherapy) reducing requirement for platelet transfusion. Contra indicated in patients with haematuria as it will prevent clot lysis in the urinary tract an d can result in clot colic. In the CRASH-2 study treatment with tranexamic acid 1g 8-hourly within 3h of trauma reduced death due to bleeding.1 Aprotinin Naturally-occurring inhibitor of plasmin and other proteolytic enzymes which has been used to limit bleeding following open heart surgery with extracorporeal circulation or liver transplantation. Currently unlicensed for this indication. Clotting factor concentrates Bleeding due to defi ciency of specifi c coagulation factors i s treated by either elevating the defi cient factor \200\224e.g. treatment of mild FVIII de fi - ciency with desmopressin \200\224or replacement of the missing factor. Recombinant fac tor VIII and IX are now available in some countries for routine use in patients with congen ital defi ciencies. For patients with rare coagulation factor defi ciencies or multiple acq uired defi ciencies, as occurs with liver disease, massive blood loss with dilutional coagu lop- athy or DIC, replacement therapy still requires donor-derived FFP. 471 BLEEDING: THERAPEUTIC PRODUCTS Recombinant VIIa and FEIBA Products used to treat patients with inhibitory antibodies to fa ctor VIII or IX. Recombinant factor VIIa also used for factor VII defi ciency and GT. rVIIa is not recommended for treatment of severe bleeding due to other causes. Reference 1. CRASH-2 (2011). The importance of early treatment with tranexamic acid in blee ding trauma patients: an exploratory analysis of the CRASH-2 randomized controlled trial. L ancet, 377, 1096 \200\223101. 472 CHAPTER 10 Haemostasis and thrombosis von Willebrand disease Commonest heritable bleeding disorder. Autosomal inheritance. Low vW F level or reduced vWF function, aff ects both sexes but presents more frequently in \231 \200 because of menorrhagia. Incidence of 1 per few hundred. Pathophysiology vWF, produced in endothelial cells and megakaryocytes, is a protein of 250k Da molecular weight. Initial dimerization and subsequent removal of propeptide allows polym erization and secretion of large multimers. The higher molecular weight (HMW) multimers, up to 20 \227 106Da, are particularly haemostatically active. vWF has 2 main functions: \200 Its principal haemostatic function is to act as a ligand for platelet adhesion and when this activity is reduced bleeding tendency increases. \200 It has a 2 function as a carrier protein for factor VIII protecting it from proteolysis. In most patients with vWD the associated mild reduction in factor VIII level i s not the cause of the haemostatic defect. Many cases of heritable/congenital vWD are currently thought to be caused by genetic mutati ons at the vWF locus but some may be due to defects in other genes which aff ect vWF levels (epigenetic factors such as ABO blood group). Increasingly, vWF is considered a continuous vari- able with low levels associated with an i bleeding tendency. VWD is classi \201 ed into 3 main types (See Table 10.1.) \200 Type 1 \200\224quantitati ve defi ciency of vWF (75% of cases). \200 Type 2 \200\224qualitative defi ciency of vWF (20% of cases). \200 Type 3 \200\224complete defi ciency of vWF (rare). Clinical features Presentation varies markedly but typically a mild-to-moderate bleeding te ndency. Symptoms may be intermittent possibly related to fl uctuating vWF levels. It may be necessary to test on repeated occasions to estab- lish that vWF levels may be abnormally l ow on occasion. \200 Bleeding type \200\224mucocutaneous, easy bruising, nose bleeds, prolonged bleeding from cuts, dental extractions, trauma, surgery, and menorrhagia. Haemart hroses do not typically occur (except in type 3). \200 Patients often present in 2nd or 3 rd decade after prolonged bleeding after dental extraction or surgery. \200 Type 2B causes thrombocytopenia. Laboratory diagnosis vWF is an acute phase protein \200\224increasing with stress, oestroge ns, preg- nancy, malignancy, thyrotoxicosis. vWF levels are dependent on ABO blood group be ing lower in group O than non-O. \200 Because vWF is the carrier protein for FVIII protec ting it from proteolysis there is a 2 defi ciency of FVIII associated with vWF defi ciency, but it is a low vWF level that is primarily responsible for bleeding in most patients. vWF level and function typically mildly or moderately reduced. 473 von WILLEBRAND DISEASE Table 10.1 Classifi cation of vWD Type VIII vWF Ag vWF activity RIPA low dose HMW multimer 1 n/d d d d/n n 2A n/d n/d d d/n d 2M n/d n/d d d/n n 2B n/d n/d d i d 2N d n n n n 3 Usually undetectable dd dd dd dd FVIII may be n, or low in some patients. Factor VIII is seldom low enough to cause the joint bleeds seen in hemophilia except in type 3 which is a severe blee ding disorder. In type 1 vWD the PT, APTT, and platelet count are often n (a 50% reduction in vWF is suffi cient to reduce platelet adhesion and cause bleeding but the associated 50% reduction in F VIII is not suffi cient to prolong the APTT). Bleeding time is often n and is no longer used as a routine test. It has been largely repla ced by automated in vitro platelet function analysis. When mild, the condition may be diffi cult to diagnose as many of the tests are n, including the VIII and variably the vWF level. Repeat testing is necessary . Family testing is useful. vWF activity measured as ristocetin cofactor activity (vWF:RCo) or collagen binding activity (vWF:CB), which is measured in plasma and is not the same as R IPA (E see p.464) which is the ability of ristocetin to agglutinate platelet-rich plasma. Type 2 often diagnosed when vWF level is low and vWF:RCo/ vWF:Ag ratio <0.7. The main subtypes of type 2 are 2A and 2M \200\224in 2A there is a qualitative defect with absent HMW multimers and in 2M there is a qualitative defect but wi th HMW multimers present. RIPA is ristocetin-induced platelet agglutination performed on a patient \200\231s platelet rich plasma. Only use of RIPA test is for detection of type 2B w hen RIPA is low due to high affi nity variant vWF which produces thrombocytopenia and reduc ed circulating level of vWF. Type 2N is rare autosomal recessive variant in which the FVIII:C carrier function of vWF is reduced. May be misdiagnosed as hemophilia A but the clue is that \231\200 are aff ected as well as \231\202 and autosomal recessive inheritance. Majority of patients will have type 1 disease which rarely causes life-threatening bleeds; may have little impact on quality of life/life expectancy. Management with vWF rich VWF/FVIII concentrates as for severe hemophilia should enable patients with severe VWD to have good QoL. 474 CHAPTER 10 Haemostasis and thrombosis Treatment \200 Mainstay of treatment is desmopressin. Avoid aspirin and NSAIDs. Mild bleeding symptoms \200\224easy bruising, bleeding from cuts may settle with local pres sure. Tranexamic acid is a useful antifi brinolytic drug (15mg/kg oral tds), e.g. for denta l extraction in conjunction with desmopressin. Vaccination against HBV and HAV recommended for all patients. \200 Inhibitors infrequent \200\224usually type 3 disease. Moderate disease and minor surgery \200 Desmopressin (0.3mcg/kg SC or by slow IV injectio n/infusion). Fewer side eff ects with SC route. Most responders have type 1 VWD but may work in some type 2 patients. Avoid in type 2B (may reduce platelets). Major surgery, bleeding symptoms, or severe disease \200 If desmopressin insuffi cient us e vWF (Wilfactin) or vWF/VIII con- centrate (intermediate purity VIII concentrate), e.g. Alphanate, BPL 8Y, Haemate P. A high purity vWF concentrate (Wilfactin) avoids extremely high FVIII levels when repeated dosing is required, e.g. surgery in type 3 patient. Monitor treatment with vWF:RCo or vWF:Ag assay. \200 Bleeding time or PFA-100 (E see p.46 4) may not correct despite good clinical response. Treat post-op for 7 \200\22310d. Pregnancy FVIII and vWF i in pregnancy so rarely presents a problem for type 1. Post-partum vWF declines quickly so watch out for PPH in moderate/ severely aff ected women. Give desm opressin or vWF concentrate to maintain levels >0.30U/mL if clinical problem. In type 2B ab normal HMW multimers can cause platelet aggregation and thrombocytopenia in pregnancy. Avoi d tranexamic acid in pregnancy/type 2B as there may be risk of thrombosis. Menorrhagia May be major problem. Tranexamic acid for fi rst 3d of the menstrual period can reduce blood loss by 50%. Combined oral contraceptive pill is useful. Levonorgestrel (horm one impregnated) coil very eff ective in some patients.