Thrombophilia
Presentation § VTE § Recurrent fetal loss and other pregnancy complications (Pre-eclampsia, placental abruption, IUGR, still birth) § Poor link with arterial thrombosis (Stroke and ACS) § Pupura fulminans § Warfarin induced skin necrosis
Risk of thrombosis increases with age § 1:10,000/yr reproductive age, 1:1000/yr age 50, 1:100/yr age 90 § Afrocaribeans > Caucasian > Asian § 25% of PEs result in sudden death
Survival after VTE
Who to test 1. Young 2. Family history 3. Recurrent thrombosis 4. Unusual site (Cerebral, mesenteric, renal) 5. Thrombosis during pregnancy 6. Idiopathic venous thromboemolism
Heritable Thrombophilia
Antithrombin deficiency § Synthesized by liver § Inhibits thrombin § IXa, Xa, XIa, XIIa, TF bound VIIa § Activity enhanced by heparins (heparin sulphate in vivo) § Chromosome 1 § Autosomal dominant
Type 1 § Quantitative reduction of antithrombin § prevalance § Majority have a thrombosis by 25 years
Type 2 § Qualitatively abnormal protein § More common § Reactive site § Abnormality in the thrombin binding site § Heparin binding site § Abnormaility in the heparin binding site § Pleiotrophic site § Abnormalities in both binding sites
Risk of thrombosis § Type 1 > reactive site > heparin site
Antithrombin assays 1. Functional assay – Heparin co-factor assay § Incubate plasma with an excess of IIa and excess heparin. AT-heparin-IIa complex formation and residual IIa measured with a chromogenic substrate § Will detect both type I and II 2. Immunological assay a. ELISA i. Reduced in type I ii. Normal in type II (may be abnormal in pleomorphic site, as antithrombin becomes unstable and is not recognised) b. Immunoelectrophoresis (Laurell rockets) i. Not used due to inaccuracy at less than 10% ii. Antigen placed in a well in an antibody containing agarose gel iii. Antigen complexes with antibody and forms a rocket of immunoprecipitate iv. Height of rocket is proportional to antigen concentration Normal ranges § Levels reduced in: § Infants/ elderly § Consumption § massive thrombosis / DIC § Loss § Nephrotic / protein losing enteropathy / inflammatory bowel disease § Drugs § Heparin / L-asparaginase/ oestrogens § Reduced production § Liver disease / malnutrition
Antithrombin concentrate § Virally inactivated § Dose is 25-50units/kg § Indications for use in AT deficiency § Thrombosis during pregnancy when AC contraindicated § Refractory thrombosis § Major surgery § DIC § Acute nephrotic syndrome § Fulminant hepatic failure § Veno-occlusive disease in transplant patients
Protein C deficiency § Vit K dependant § Synthesized by the liver § Activated by thrombin-thrombomodulin complex on the surface of endothelial cells § Thrombomodulin is transmembrane, therefore effects are localised § Thrombin is converted from a pro-coagulant to an anticoagulant § APC then binds to cofactor protein S § Degrades activated Va (VaXa complex) and VIIIa (VIIIa/IXa) = major inhibitor of coagulation § APC+PS enhances fibrinolysis by preventing degradation of t-PA by PAI-1 § Also cleaves V forming anticoagulant V, which functions in synergy with protein S and APC in the degredation of FVIIIa § Reduces platelet prothrombinase activity
§ Autosomal dominant inheritance § Homozygous deficiency may manifest as purpura fulminans § Susceptible to warfarin-induced skin necrosis § Start warfarin after heparin and at low doses
Type 1 § Quantitative § More common Type 2 § Qualitative § No phenotypic difference apparent, so classification not clinically apparent
Protein C assay § Functional § Chromogenic methods § simple § detect all type 1 and most type 2 § not affected by other coagulopathies § over estimates with warfarin § preferred test § Clotting methods § Low levels in the presence of FVL, high FVIII and hyperlipidaemia § May be unreliable in the presence of a lupus inhibitor and heparin § Under estimates with warfarin § Antigen assays § Will distinguish between type 1 and 2, but not clinically warranted § May be useful if on warfarin
Normal ranges § Diagnosis can be difficult as there is wide overlap in protein C activity between normal individuals and heterozygotes § Heterozygotes usually 30-60% § Homozygotes usually <`10%
Acquired deficiency § Consumption § DIC / thrombosis / TTP § Reduced production § Liver disease / Vitamin K deficiency § Drugs § L-asparaginase/ warfarin § Neonates § IgG paraprotein (=inhibitor of PC) § Unchanged (or even increased) during pregnancy (OCP)
Protein S deficiency § Vit K § Synthesized by liver and endothelial cells § Cofactor for activated protein C § 65% is complexed with C4b-binding protein = no activity § Bioavailability of protein S is linked to C4bBP concentration § C4bBP is an acute phase reactant (free PS reduced in inflammatory conditions) § Homozygous may manifest as purpura fulminans § Chromosome 3 § Autosomal dominant
§ Type 1 § Quantitative § Type 2 § Qualitative § Type 3 § Reduced free protein S § Normal total protein S
Protein S assay § Functional – clotting assay § Based on cofactor activity § Should only reflect free protein S § Detect all types § False positives with § APCR (FVL and APL) – as it relies on the patients own FV and FVL is common § Antigenic assay § ELISAs and radioimmunoassay an immunoelectrophoresis (rocket) § Should not be influenced by concentration of C4bBP § Can meaurse total and free protein S § Preferred test § Free protein S assay § Should be performed when a functional assay yields a low result
Normal ranges § Low levels § Women lower levels / neonates § Pregnancy § APLa / HIV / SLE § Drugs § COCP / HRT / warfarin § Consumption § DIC / Acute thrombosis § Inflammation § Increased C4b-BP results in low free PS § Reduced production § Liver disease / Vitamin K deficiency
Activated protein C resistance § Impaired plasma anticoagulant response to APC added in vitro § Most common cause is FVL (>90%) § Point mutation in FVa imparts resistance to proteolytic action of APC § Other causes § High FVIII, APLa
Normal ranges § Increased resistance with § Age § Women § OCP / HRT § Pregnancy
§ APC resistance tests § APTT with and without added APC expressed as a ratio (APC/ SR) § Normal result = 3 times longer with APC § The greater the resistance the lower the APC/SR § Modified by diluting patient plasma with factor V deficient plasma to correct any deficiencies or excesses of clotting factors in the patient sample § Important to avoid platelet contamination § Relies on otherwise normal coagulation of the patient plasma § Not diagnostic of FVL § Abnormal in acquired APCR § High F8, LA, factor deficiencies, OCP, pregnancy etc § Modified APC test (in FVL deficient plasma) is more specific for FVL in the absence of genetic testing, but may miss other causes of APCR § The clinical relevance of detecting APCR in the absence of FVL is not known
§ FVL detection § Genetic analysis § Amplification of the exon /intron boundary in exon 5 of the factor V gene
Prevalence of factor V § 2-15% § Northern European § Heterozygotes § RR = 3-8 fold § Homozygotes = 80 fold § Familial APC resistance in absence of FVL § Eg. Factor V Cambridge, factor V Hong Kong
Prothrombin G20210A mutation § G to A at nucleotide 20210 of the prothrombin gene § Elevated plasma prothrombin levels § Genetic analysis to detect § Higher in Southern than Northern Europe § Most common heritable thrombophilia in Southern Europe § Heterozygotes – RR = 3 fold
Dysfibrinogenaemia § 20% have an increased tendancy to arteriovenous thrombosis § Abnormal fibrinogen generates fibrin that is resistant to fibrinolysis § Plasmin resistance § Impaired thrombin binding, increasing free thrombin resulting in increased fibrin formation § 25% have a bleeding tendancy § Plasma concentration may be low
Elevated factor VIII levels § >150iu/dL 6 fold risk cf. <100 § Increased risk with factor IX, X and XI have also been described
Hyperhomocysteinaemia § >18.5umol/l = 2.5 fold risk § Increased risk of venous and arterial § Homocysteinuria = rare homozygous genetic disease § Neurlogical defects, marfanoid features, ectopic lens, premature atherosclerosis § Increased levels of homocysteine with reduced § Folate § Cobalamin § Pyridoxine § ESRF, renal transplant and CsA § Treatment § Folic acid § MTHFR contributes to hyperhomocysteinaemia but is itself not associated with VTE § MTHFR converts homocysteine to methionine
Testing § Delay until 1 month after completion of anticoagulation § Avoid during § Intercurrent illness § Pregnancy § COCP / HRT § Should include thrombin time (dysfibrinogenaemia) and prothrombin time (may help in interpretating protein C and S levels)
Management of acute events § Heparin for a minimum of 5 days § Rarely protein C and S deficiency can be associated with warfarin induced skin necrosis (and neonatal purpura fulminans) if under anticoagulated with heparin when warfarin introduced § Neonatal purpura fulminans in association with protein C deficiency requires Protein C replacement (or FFP if protein S) as well as anticoagulation § Risk of recurrence after a first event in unselected patients = 15-20% at 2 years § Risk of major haemorrhage on AC is 1%/ year § Heterozygotes for FVL and prothrombin G20210A don’t appear to have a higher rate of recurrence than the general population § Secondary prophylaxis after a single event probably not warranted § Type 1 AT or combinations may warrant long-term AC after a first event
Thrombosis prevention § Past history of VTE § Consider prophylaxis for high risk periods § Affected but asymptomatic relatives of symptomatic patients § Consider prophylaxis for high risk periods § Consider extended prophylaxis after high-risk surgery
Contraceptive advice § OCP not recommended for people with a personal history of VTE or VTE in a first degree relative § Largest effect is with 3rd generation OCPs § Limited evidence but most would recommend a progesterone only containing method
Pregnancy § 0.9 per 1000 deliveries § 50% of gestational VTE are thrombophilia associated § Risk is greater post partum § Risk factors § Age (> 35) § High parity (>3) § Intercurrent illness § Immobility § Caesarean section § UFH, LMWH and danaparoid do not cross placenta § Heparin preconceptually § Partnerships that have proved their fertility § Unwilling to accept possible risk of warfarin § Warfarin embryopathy § Nasal hypoplasia, stippled epiphyses 6-12 weeks § CNS abnormalities at any stage § Substitute to heparin when conception confirmed § Aim to discontinue warfarin by 6 weeks § High risk § Long term anticoagulation § Type 1 or type 2 reactive site AT deficiency – 40% (regardless of previous thrombosis) § Compression stockings during and 6-12 weeks post partum § Clearance of heparin is increased during pregnancy § LMWH 75 anti Xa units/kg bd § Allow 24 hours before epidural § Check platelet count before and after 4 days § Check anti-Xa after 1st month and then 4-6 weekly § Restart AC 12 hours post delivery § May convert to warfarin on day 1 or 2 post partum § Warfarin and heparin are safe for breast feeding § Moderate risk § Previous VTE (regardless of thrombophilic defect) § FH of VTE and heterozygous for protein C, homozygous for FVL or prothrombin or combinations § Compression stockings during and 6-12 weeks post partum § Fixed prophylactic dose of LMWH § Allow 12 hours before epidural § Anti-Xa levels not needed § Low risk § Asymptomatic with thrombophilic tendancy § Previous VTE associated with a temporary risk factor § Compression stockings during and 6 weeks post partum § Consider AC pre-delivery and post partum
§ If VTE 4 weeks or less before delivery, consider a retrievable IVC filter or switching to UFH at time of induction to reduce time without AC cover
Prenatal diagnosis § Only considered appropriate where foetus at high risk of severe thrombophilia § Homozygous AT deficiency may be incompatible with life
§ HRT and selective oestrogen receptor modulators are associated with risk of VTE
Arterial thrombosis § Slight increased risk with FVL and prothrombin § Hyperhomocysteinaemia
§ Fibrinolytic system abnormalities
§ Plasminogen activator inhibitor-1 § Major inhibitor of tissue plasminogen activator tPA § Increased PAI-1 is associated with atherosclerotic risk § Probably not an independent risk factor, may be associated with insulin
§ Tissue plasminogen activator § Increased risk of MI has been reported
§ Neither PAI-1 nor tPA have been associated with venous thrombosis
§ Platelet membrane glycoproteins
§ GP IIb/IIIa § PLA1/PLA2 polymorphism § Weak association with MI in young patients
§ GP Ia/IIa § Some association with MI and stroke
§ GP Ib/IX/V § Variable study outcomes § Possible link with MI, stroke
Acquired thrombophilia
§ Active cancer § Myeloproliferative diseases § Chemotherapy § Lupus anticoagulant § HIT § DIC § OCP / HRT § Pregnancy / post partum § PNH § Antiphospholipid syndrome § Nephrotic syndrome § Inflammatory bowel disease § Becets § Thromboangitis obliterans (Buerger’s disease)
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