Thrombophilia testing: A British Society for Haematology guideline

Abstract

This guideline was compiled according to the BSH process at [https://b-s-h.org.uk/media/16732/bsh-guidance-development-process-dec-5-18.pdf]. The Grading of Recommendations Assessment, Development and Evaluation (GRADE) nomenclature was used to evaluate levels of evidence and to assess the strength of recommendations. The GRADE criteria can be found at http://www.gradeworkinggroup.org. A literature search was carried out using the terms given in Appendix S1 until April 2021. Review of the manuscript was performed by the BSH Haemostasis and Thrombosis Task Force, the BSH Guidelines Committee and the sounding board of BSH. It was also placed on the members section of the BSH website for comment. It has also been reviewed by Royal College of Obstetricians and Gynaecologists, Royal College of Paediatrics and Child Health, Royal College of Physicians and Thrombosis UK, a patient-centred charity dedicated to promoting awareness, research and care of thrombosis; these organisations do not necessarily approve or endorse the contents. This guideline updates and widens the scope of the previous British Society for Haematology (BSH) Clinical guidelines for testing for heritable thrombophilia1 to include both heritable and acquired thrombophilia. The term thrombophilia is generally used to describe hereditary and/or acquired conditions associated with an increased predisposition to thrombosis. Heritable thrombophilia refers to genetic disorders of specific haemostatic proteins. These guidelines focus only on the factors that are identified from laboratory testing and therefore exclude disorders such as cancer, inflammatory conditions and obesity that are associated with thrombosis through multiple mechanisms. The most clearly defined heritable thrombophilias are the factor V Leiden (FVL) variant (F5 G1691A), the prothrombin gene variant (F2 G20210A), protein C (PC) deficiency, protein S (PS) deficiency, and antithrombin (AT) deficiency.2 Important acquired thrombophilias include the antiphospholipid syndrome (APS), paroxysmal nocturnal haemoglobinuria (PNH), myeloproliferative neoplasms (MPN) and the presence of a JAK2 mutation in the absence of an MPN phenotype. Pregnancy is a hypercoagulable state due partly to physiological changes in both the coagulation and fibrinolytic systems. Heritable and acquired thrombophilias can interact to further increase the risk of thrombosis, for example during pregnancy and the puerperium. As there is evidence that some thrombophilias may be associated with pregnancy failure and complications, testing for this purpose is included. Elevated levels of procoagulant factors may increase the risk of thrombosis but the relationship is not straightforward. First, part of the variance is genetic, and therefore lifelong, but some is acquired so that comorbidities such as obesity or inflammation confound the estimate of effect. Second, some factors, most notably factor V (FV), have anticoagulant effects that counterbalance a procoagulant effect from their elevation. A meta-analysis of 12 genome-wide association studies (GWAS) for venous thromboembolism (VTE) identified variants in F2, F5, F11, and FGG (encoding fibrinogen gamma chain) linked to thrombosis as well as non-O alleles of ABO which mediate their effect via elevation of von Willebrand factor (VWF) and secondarily factor VIII (FVIII).3 This approach does not detect rare variants with functional effects increasing thrombotic risk as reported in factor IX (F9), factor II (F2) and fibrinogen-alpha (FGA), fibrinogen-beta (FGB), and FGG.4-6 However, the relevance of these genetic variants to routine clinical practice is not clear at present. A phenotypic analysis was carried out as part of the Multiple Environmental and Genetic Assessment (MEGA) case–control study of VTE. After adjustment for age and sex, levels of factors II, X, IX, XI, VIII and fibrinogen all showed a positive association with risk of thrombosis. After additional correction for FVIII levels, only FIX and FXI retained significance with odds ratios (ORs) for levels >95th centile of 1.8 (95% confidence interval [CI]: 1.1–2.9) and 1.8 (1.1–3.0), respectively. In contrast, the OR for FVIII>95th centile was 16.0 (9.7–26.3) after correction for age, sex, and all the other coagulation factors.7 However, because of interacting heritable and acquired influences on FVIII activity, variability in levels over time, and as yet, lack of evidence of a role in the management of individuals with thrombosis or asymptomatic family members, routine testing for FVIII is not currently recommended. Despite results from animal studies, there remains no genetic or phenotypic8-10 evidence that variation in FXII is associated with thrombosis in humans.11 FXIII has a complex relationship with thrombosis due to interactions with other factors and the effects of genetic variants on FXIII activity assays. Genetic studies showed that the Val24Leu variant was associated with a reduced risk of venous thrombosis (OR: 0.85; 95% CI: 0.77–0.95).12, 13 The associations of PC, PS and AT deficiencies with increased risks of VTE are well-established.14 The degree of deficiency is variable and sensitive to assay type but in general thrombosis risk rises as soon the levels of protein C, S or AT fall below the normal range. In contrast, although tissue factor pathway inhibitor (TFPI), heparin cofactor II, and protein Z-dependent protease inhibitor (ZPI) and its cofactor, protein Z, are also natural anticoagulants, the clinical significance of genotypic or phenotypic variation in these is uncertain and testing for clinical purposes is not recommended. Guidelines on laboratory aspects of testing for deficiencies of natural anticoagulants have recently been published by the British Society for Haematology15 and the International Society on Thrombosis and Haemostasis.16-18 The risk of a first episode of VTE is increased around 15-fold in heterozygous AT deficiency.19 Overall, the risks are similar in those with type I and type II defects with the exception of most type II heparin binding defects, which appear to have a 4-fold lower risk.19 In contrast, homozygous heparin binding site defects appear to be associated with a high thrombotic risk.20 Further differences within antithrombin subtypes have also been observed.21 However, data on differences in risk between and within different subtypes are limited, and findings vary according to study design, the population being studied (family or non-family members), and whether all or only unprovoked venous thrombotic events were included in the analysis. In those with heterozygous PC or PS deficiency, the risk of a first episode of VTE is increased around 5–7-fold.19, 22, 23 There are no clinically useful differences in thrombotic risk between type I and type II PC deficiency15 and no clear evidence of a difference in risk between different subtypes of PS deficiency. These risks for heterozygous PC and PS deficiency are similar to or greater than those associated with FVL variant or F2 G20210A variant, but deficiencies of the natural anticoagulants are much less common (population prevalence of <0.5% for each deficiency), at least in those of European origin, and contribute relatively little to the population burden of VTE. Deficiencies of physiological anticoagulants interact with acquired risks and a transient provoking factor is present in approximately 50% of episodes of VTE in genetically predisposed individuals.24, 25 Since deficiencies of these natural anticoagulants are caused by multiple different genetic variants, clinical laboratory assessment is generally based on measurement of plasma activities or concentrations rather than molecular of deficiencies be testing and results may not be to a heritable deficiency. include and the of anticoagulants the has been to for deficiencies of physiological anticoagulants, this be performed only after of for thrombosis, as there is over the of the results to testing and increased and with there being no evidence that influences C activity assay S protein S activity assay and normal from of deficiency coagulation increase or heparin using assay V Leiden using assay normal from Pregnancy and of deficiency syndrome coagulation thrombosis or increase or heparin using V Leiden using assay normal from a of coagulation syndrome thrombosis increase using assay using assay The FVL and F2 G20210A variants are the most genetic variants to These are using prevalence in of different for FVL is present in of individuals of European but is rare or in from and of the and for the prothrombin gene variant is present in of and is rare or in other The FVL variant a site for PC in factor V increasing procoagulant The prothrombin gene variant is a mutation in the of the increased levels of These variants in increased risks for first venous thrombosis of and A of variants in other with a of have been reported to an increased risk of thrombosis. These include variants of (encoding inhibitor type and factor as well as variants linked to the changes in procoagulant factors However, their association with thrombosis is not or their effect is to management and not be included in thrombophilia at present. has been that multiple variants present in an can to a risk of this and do not and to this nocturnal haemoglobinuria and myeloproliferative neoplasms (MPN) are acquired genetic that increase the risk of thrombosis. is an acquired by the of a population of in due to gene mutation in a deficiency or absence of all and on the of to in the clinical of and to of with present with thrombosis. The with thrombosis risk and with a of over 50% have a of thrombosis of to in those with a of are by of an and include and MPN or presence of a by a JAK2 mutation in the absence of an MPN are associated with and venous The associated with and MPN can in the venous or but in for thrombosis and thrombosis, and the syndrome and venous thrombosis In thrombosis the mutation in JAK2 are found in 95% of an 12 mutation in most and in of and JAK2 in approximately of the general population an MPN and in of with with no MPN A of positive for JAK2 mutation with normal at MPN during of are present in of those with or In JAK2 or of those with and of those with are positive for a gene In a study by of with or the of thrombosis associated with with and was and and was that of with and the mutation The of thrombosis associated with the JAK2 12 and are not well due to the of with these for variants in is sensitive and are not on used for of JAK2 is in of is based on analysis using The of is on the presence of at least clinical or pregnancy and at least laboratory of antiphospholipid which include anticoagulant or or The to be that present on or at least 12 the a positive to be the most associated with thrombosis, but individuals are positive for all have the thrombotic the BSH guidelines on the and management of antiphospholipid syndrome that in with thrombosis, does not useful both and and are part of the on laboratory criteria for There is increasing evidence that and have a role in with In with thrombotic as to the risk in with an to VTE and in those with venous to an There is increasing evidence that the risk of VTE by risk factors is similar to that with unprovoked such may also from as in those with unprovoked VTE. As the presence of antiphospholipid may management of in these may be to for antiphospholipid is a but variant of by of thrombosis at multiple to to in with positive Recommendations on the and antiphospholipid testing venous or thrombosis are in the to British Society for Haematology Guidelines on and of In asymptomatic individuals with positive antiphospholipid identified because of a or presence of an the of first thrombotic events were between venous and was to be of thrombosis of and have been in asymptomatic positive individuals and in with the antiphospholipid In the clinical of testing is not testing is clearly not is defined as the of a to clinical It is that are in of on whether or not to This include of the of testing and management is the of a heritable in a has a venous thrombotic in their management or the management of asymptomatic family The risk of for VTE is less than that for a first episode of thrombosis because the is the risk is and no clinical have been There are data on the association of FVL and F2 G20210A variants with risk of in the population of with data that FVL Leiden but not F2 G20210A is associated with an increased risk of However, in a study with of with a first unprovoked of FVL and a F2 G20210A After adjustment for age, sex, and of as a at the FVL 95% CI: the F2 G20210A mutation 95% CI: was associated with venous thromboembolism to with natural anticoagulant deficiencies were from studies from which for VTE after of for a first were A meta-analysis of individuals with AT deficiency the odds of were increased with an risk anticoagulant of (95% CI: for and (95% CI: for VTE A further study in which AT was in on only found the odds of VTE were increased (95% CI: in those with AT activity centile and (95% CI: in those with AT activities of In a study of the risk of VTE in not anticoagulant was (95% CI: in those with PC deficiency and (95% CI: in those with PS In a the odds of VTE were increased (95% CI: in PC and (95% CI: in those with PS deficiency the of were and with FXI activity between the and or with the factor VIII a for of (95% CI: to those with FVIII In terms this to a of to these effects are their is Clinical in with such as in can those risk of is high to and which is not by the absence of a These factors also with risk of not in the presence of heritable There is no evidence that the presence of heritable thrombophilia influences the or the of anticoagulant thrombosis in those with AT In AT deficiency, specific which can be and can also of laboratory of this is a rare and so routine testing is not in the absence of a family as or with with a and/or family of thrombosis in the absence of a clear risk genetic analysis via is as and be with phenotypic testing The of a genetic with the strength of the family The heritable with variable of FVIII and FXI have clear genetic but also acquired so the of being is less of a heritable in a family does not a risk of thrombosis high to and does not most However, some guidelines include of heritable in their risk assessment with a on of that in a family their risk of thrombosis but does not to normal and the of testing on their and the of the VTE Overall, the risk for VTE is by the clinical with risk factors and rather than the thrombophilia a is to have a heritable may be to testing of this their management for deficiencies of PC, PS or AT deficiency in a of for FVL is not in with a first degree with FVL but no of thrombosis or to or However, the of family of thrombosis, thrombophilia testing and risk of thrombosis of be with all to whether their and be and management of thrombosis at are in BSH thrombosis at which or conditions the testing for thrombophilia be for with The association of MPN and with thrombosis at which thrombosis and the has been in and these disorders be for in the absence of a clear for the such as or of data from found that in of thrombosis the of the thrombosis at a of after of and MPN is because these have specific in to to thrombosis. In a and meta-analysis of studies to assess the prevalence of heritable thrombophilia in with and the prevalence of PC, and PS deficiencies were and in and and in respectively. studies the prevalence of heritable thrombophilia between and The odds ratios of heritable PC and PS deficiencies for were (95% CI: (95% CI: and (95% CI: These studies are only for the first thrombotic and the risk of events associated with heritable thrombophilia and thrombosis at is not well but to be the of testing for heritable thrombophilia is and testing be only the thrombotic in the absence of a clear risk factor for the at a age is a rare for of all The of have an risk the most common of which are and rare that can contribute to include inflammatory and factors such as or is reported in of with and around of with of with are found to have a JAK2 mutation with normal at are reported in to of with However, is not clear of these a normal at with studies have the presence of the risk of thrombosis at such as and As the type and of are by the presence of antiphospholipid testing for these is in an BSH In the absence of a clear risk with may and routine testing for heritable thrombophilia is not There is no evidence to an association of heritable thrombophilia with The role of antiphospholipid in is A meta-analysis of studies showed that presence of antiphospholipid was associated with of 95% CI: A study that included with and also showed that antiphospholipid were in than in OR 95% CI: with anticoagulant or positive antiphospholipid than for may be in risk factors and no other for such as and as those with positive be for There is evidence with to the presence and the strength of associations between FVL and F2 G20210A variant and thrombosis. some studies a increased risk of in with FVL or F2 G20210A variants, this has not been in S1 on the association of the FVL or with These variants are common in the European population and be found in with their presence a role for events is not and is to from these associations have been these have been to be of clinical significance and there are no clinical to that management be as a of the presence of these heritable deficiencies of PC and PS are studies with to assess associations with risk of thrombosis are Overall, there is no evidence to an association between heritable thrombophilia and thrombosis in and no evidence that testing for heritable thrombophilia is not in with thrombosis. thrombophilia such as and MPN increase the risk of both venous and thrombosis thrombosis for of thrombotic events to for antiphospholipid MPN and be in with thrombosis in the absence of other risk factors or in and in those with an MPN and as this may have a on The association of or antiphospholipid with is a of due to the of and the that risk factors for may The prevalence of from to and that of antiphospholipid with as defined by clinical The prevalence of asymptomatic defined in terms of on in with to in and in normal The of thrombophilia in remains a of and thrombophilia testing can in and an identified thrombophilia may not necessarily be the of and can of term the studies the risk of associated with acquired and heritable thrombophilia. Heritable disorders of such as and with and are not associated with and are not in this In a of studies in PC, PS and AT deficiency, FVL and F2 G20210A not a clear relationship with However, in a of studies that included from to there was a but association with in for AT deficiency not The this was not evidence of a relationship evidence for on clinical in thrombophilia at least positive most factor VIII or and but these findings only management in of the for However, testing was performed in the functional have not been of a of in positive in but thrombophilia was in only and management in only of thrombophilia testing the high and at least positive most factor VIII activity or PS activity are to clinical management in only these thrombophilia most not of for The role of thrombophilia testing by is with on prevalence of heritable thrombophilias in with and There is currently no clear evidence to an additional of thrombophilia testing in with myeloproliferative neoplasms have been in thrombosis. of MPN is because specific is to In an study identified with and after a of thrombosis. age thrombosis and presence of JAK2 were The JAK2 variant may be the is Thrombosis in in of and the reported of in with was around an risk factor in the first after with a high risk of in are In a study of with at least assay for was positive in which positive in only after 12 for antiphospholipid syndrome was in most due to the of A of and from studies the presence of antiphospholipid in with Overall, of with and with transient antiphospholipid out of studies reported associations between and the events with a OR of (95% CI: to The reported of VTE in is to In the is increased to to The most common age for VTE are and than of with VTE have than risk with venous being the most common risk for over of VTE and over 50% of The role of testing for heritable thrombophilia in VTE is not A 13 from to the role of heritable thrombophilia in VTE. The that VTE is and clinical risk factors a greater role than heritable in associated In an the prevalence of heritable thrombophilia in with VTE was no different than that of the that with VTE for heritable thrombophilia was not In contrast, in study of of with VTE at least heritable In an of a heritable thrombophilia was found in of with an VTE in the first of heritable thrombophilia to be present in some with both venous and the role of heritable thrombophilia testing in with VTE does not currently appear to the type or of In contrast, some are of the that thrombophilia testing be in and there is a family or with unprovoked and or thrombosis and in no factor is As for the identified heritable defects include PS deficiency, PC deficiency, AT deficiency, FVL and the F2 The heritable thrombophilias that may thrombotic risks in are homozygous type AT deficiency and homozygous or heterozygous deficiency of PC, PS or FVL or F2 G20210A PC and PS deficiency can in heterozygous or heterozygous and a deficiency of these has been linked with for PC and PS in of is as or plasma in of PS can be for and of further VTE. In of AT deficiency, of AT with AT is to further thrombosis and to anticoagulant effect of is rare in of to with these the of thrombosis rare in these thrombosis in be due to and testing for antiphospholipid be As in testing for and levels not be included in thrombophilia of are present. Pregnancy is an acquired hypercoagulable The of VTE in pregnancy or the is around in a to increase in to an This rises further in the first to a to increase in thrombosis remains the of in or recently in the and thrombosis in pregnancy is rare with an as is common than in to testing for be the for and family members, of a positive or testing is is that this is As in other testing only be is to in have a previous unprovoked or in or routine thrombophilia testing is not as pregnancy and the puerperium. There is no evidence to of asymptomatic with a family of thrombosis in the absence of a heritable thrombophilia. In with a first degree with PC, PS or AT deficiency of these may However, these are rare and for these deficiencies is not by for AT is there is evidence of heparin individuals to a the of is to be an of heparin based on and A and the risks of a first episode of VTE in pregnancy with different heritable The that based on a risk of with PC or PS deficiency or with homozygous FVL be for in pregnancy and the puerperium. with heterozygous heterozygous F2 or for both FVL and F2 G20210A generally not be on the of thrombophilia and family than for heterozygous the data were to further of risk during the and in the presence or absence of a family and confidence were The risk was with antithrombin deficiency, and a study of with type I antithrombin deficiency found a high risk in the absence of a family thrombosis is rare in pregnancy but given the association of with both and venous thrombotic events in this testing for antiphospholipid be to It is to have a variation in the of antiphospholipid during pregnancy and testing is performed during the results be with as or positive results during pregnancy do not exclude or a of be performed at least after the of pregnancy and 12 from the first to the positive A of studies have found associations between heritable thrombophilia and pregnancy such as and and pregnancy and the published literature is have to a of molecular heparin and/or to pregnancy guidelines for the College of Obstetricians and testing for heritable thrombophilia in with previous pregnancy thrombophilia does appear to be associated with pregnancy antiphospholipid and anticoagulant with and and and were to be common in a previous thrombosis to was also associated with positive In with previous thrombosis and positive with and is associated with pregnancy However, in with and a of previous not appear to an additional over The of to with and to a in pregnancy to lack of evidence to the significance of variants and plasma levels in the risk of thrombosis, there is no role of testing these in with pregnancy the evidence for the of with previous pregnancy is to for antiphospholipid the to and the The to for in the literature members of the BSH Haemostasis and Thrombosis Task at the of this guideline and The to the BSH sounding and the BSH Guidelines Committee for their in this The BSH the during the of this have a of to the BSH and Task which may be on of the have of to of the the evidence that the strength of the in this or The be reviewed by the Task and the literature search be to search for evidence that may have been The be and from the BSH guidelines website are an be published on the BSH guidelines website the and in this is to be and at the of to the the BSH the for the of this can be found for to S1 The is not for the or of by the than be to the for the

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