Thrombophilia screening revisited: an issue of personalized medicine

Thrombophilia—θρομβοφιλία—originating from Greek is a term meaning both affinity (-philia: φιλία) and blood clot (θρομβο). Thrombophilia indicates an increased tendency to form pathological intravascular venous or arterial thrombosis, mainly as a consequence of interaction of multiple inherited and/or acquired predisposing factors [1]. The coagulation system—usually in a balance between pro- and anticoagulant influences—shifts towards a pro-thrombotic state which may become clinically manifest as a thromboembolic disease [2]. The clinical complexity to understand the in-vivo mechanism(s) shifting the coagulation into a pro-thrombotic state—i.e. a state with an excessive thrombin generation—is the result not only of numerous coagulation factors and their interactions, but also the result of their dynamic interactions with blood vessels, endothelial cells, platelets and other cells in the circulation. Venous stasis from impaired blood circulation was already described from Rudolf Virchow in 1856 as one of the main etiologic factors for venous thrombosis [3]. Although the role of venous stasis was accepted, the link between stasis and thrombosis for example after a long flight or immobilization remained for long time elusive [4‐6]. A reduction of the fibrinolytic capacity is conceivable [7] but evidence in the human model is lacking [8]. The interactions between coagulation and other humoral systems such as complement [9] and immune system [10] are ongoing and complex. The risk of thrombosis increases ultimately with age as a consequence of punctual and constant influencing factors [11]. Venous thromboembolism (VTE) is therefore considered a multifactorial disease [12] and the final clinical sign of interaction of single or multiple genetic, epigenetic and/or acquired predisposing factors [1, 13]. Therefore, focusing on and screening for hereditary thrombophilia should represent a comprehensive evaluation of the patient’s pro-thrombotic state and not a purely laboratory testing.

Despite the association of genetic risk factors with VTE, screening for inherited thrombophilia has not shown a direct clinical benefit in the management of these patients [14]. The lack of preventive and therapeutic consequences after the first thrombotic event reduced the indications for thrombophilia screening [15, 16]. Indeed, not testing blindly for thrombophilia in patients with VTE is on the Choosing Wisely list endorsed by many scientific societies [17‐19]. But, it seems that the books are still not closed. In the era of big-data acquisition and genome-wide association studies (GWAS), it might be that newer aspects concerning risk evaluation for thrombosis come into consideration, based on the influence of newly identified genetic variations linked to thrombosis.

In this contest, in order to act against an indiscriminate, universal, population screening and to limit medical expenses we suggest to first carefully select the patient. In this review, based on evidence and personal clinical experience, we propose arguments favoring an individual decision-making regarding thrombophilia screening only in selected patients with VTE.

VTE includes the deep venous thrombosis (DVT) in typical or atypical localization and pulmonary embolism (PE). VTE may be divided between provoked (secondary) and unprovoked (idiopathic) (Table 1). Risk factors for provoked VTE are major, minor, transitory (reversible) or persistent (irreversible) (Table 2). Differentiation between idiopathic and secondary VTE is important because it affects the decision on the duration of antithrombotic therapy [20].

Genetic risk factors for VTE are deficiencies of natural anticoagulant proteins (antithrombin deficiency [21], protein C deficiency [22], protein S deficiency [23]), genetic dysfibrinogenemia [24], hyperhomocysteinemia [25] or mutation of factor II (F2, G20210A mutation [26]) or factor V-Leiden (F5, G1691A mutation [27]). GWAS revealed several additional genetic polymorphisms with borderline but measurable statistical association with VTE [13, 28]. The non O-blood group status is in this sense the most common mild predisposition [29‐31]. Two VTE associated loci, TSPAN15 and SLC44A2, increase also slightly the odds ratio for VTE (1.31 for TSPAN15 and 1.21 for SLC44A2, respectively) [32]. A comprehensive review about the genetics of VTE describing the allele prevalence and influence on VTE of various genetic variances was recently published [33]. The ThromboGenomics group in the United Kingdom using next generation sequencing and a high-throughput screening panel for genetic analysis of patients with coagulation, platelet or thrombotic disorders was able to identify a genetic diagnosis in 48.9% of patients with thrombotic disease [34].

Hereditary thrombophilia predisposes to an imbalance of the coagulation mechanisms. The cumulative prevalence of hereditary thrombophilic defects in the general population is not rare [35, 36] (Table 3). Still, these defects should be excluded only in patients with a specific indication. Inherited thrombophilia in combination with acquired thrombophilic risk factors—which may be transient or persistent [37]—may lead to VTE at young age. Inherited thrombophilia has a different impact on the relative risk of first VTE or recurrence: hereditary thrombophilia increases the relative risk of the first thrombosis, while the risk of recurrence is marginally but still not negligibly affected [38] (Table 4).

The risk of VTE in children is low with two peaks in neonates and adolescents [39]. Risk factors for VTE in these two categories of patients are sepsis, dehydration, congenital heart failure, congenital anomalies of vena cava inferior and the use of catheter interventions [40]. In addition, cancer, polychemotherapy, immobilization after surgery or plaster casts, obesity, rheumatic disease, infection and use of oral contraceptive pills in girls were the leading triggers in adolescents [41]. Although one or more of these risk factors are often present in the majority of children with VTE, inherited thrombophilia is significantly associated with the first VTE [41, 42]. Furthermore, a significant association with recurrent VTE in children was found for protein C, protein S, and antithrombin deficiency; the factor II mutation and the combination of two or more genetic traits [41]. In neonates with purpura fulminans, skin necrosis or idiopathic VTE, as well as adolescents with idiopathic VTE, thrombophilia screening is strongly recommended [43].

Thrombophilia screening—generally performed after a thromboembolic event—is not only a laboratory test for inherited diseases. Thrombophilia screening in adults should be a comprehensive evaluation of the patient’s pro-thrombotic state, allowing to determine the etiology of VTE, to estimate the risk of recurrence, to recommend therapy or prophylactic measures for patient or descendants. These objectives cannot be achieved by purely performing laboratory tests. The clinical evaluation of thrombophilia is based on personal and family history, clinical examination and basic laboratory diagnostics. It is a physician’s task to advance step by step in the evaluation and then to decide if indicated to perform—or not—genetic tests. We suggest to split-up the thrombophilia screening into clinical thrombophilia evaluation and laboratory testing, in particular genetic (Fig. 1).

Universal screening of the general population to assess the venous thrombosis risk is unjustifiable [53], expensive and should be avoided [54, 55]. Consensus exists that universal unselected screening of young women before prescribing estrogen containing oral contraceptives is clearly not indicated [56]. The low prevalence in the general population of thrombophilia genetic defects requires a high number of patients to find out a mutation and even more to avoid one VTE. A source of trouble in clinical practice is the incorrect prescription of the screening test: some tests are frequently omitted and a negative thrombophilia screening may give a false hope. We strongly suggest to avoid thrombophilia screening in this scenario, especially true partial screening, because it is clinically futile and expensive [57]. First, we advise to assess the personal and patient’s family history of VTE. If a relative has had a VTE, it is important to ask at what age and in what context. A strong family history of VTE and/or relatives with VTE before 50 years make inherited thrombophilia more likely and laboratory testing should be certainly considered. We advise, whenever possible, to screen the Index patient. In all other cases thrombophilia screening is not indicated (Table 7).

Knowledge of inherited thrombophilia may be important for young patients to avoid supplementary risk factors for VTE. Particularly smoking, dehydration, immobilization, estrogen containing medication (combined oral contraceptives or postmenopausal hormone replacement) should be avoided [37]. If chemotherapy is necessary, the treating physician should evaluate drug prophylaxis against VTE. After stopping anticoagulant therapy, in risk situations like pregnancy, acute illness, surgery, immobilization or long flights over 4 h a thromboembolic prophylaxis should be evaluated and respectively given [20]. Knowledge of the relative risk of possible pregnancy complications associated with the thrombophilic trait help in the clinical decision and management [58]. Particularly, a prophylaxis with low molecular weight heparin, Aspirin, substitution of coagulation factors and/or other management procedures should be implemented according to anamnesis, genetic defect and thromboembolic risk [59]. For each patient assessment of the individual risk during pregnancy and puerperium and a comprehensive evaluation of potential pregnancy complications depending on the genetic defect may help in the clinical decision [60]. Moreover, diagnosis of antiphospholipid syndrome either isolated or associated to other autoimmune disease like systemic lupus erythematosus (SLE) in females of childbearing age is important to evaluate preeclampsia, fetal loss, and preterm birth that are well-known risks in such pregnancies [61]. Women with antiphospholipid antibodies or antiphospholipid syndrome and lupus nephritis represent a group with high risk for obstetric complications. Factors such as appropriate preconception counseling, medication adjustment, strict disease control prior to pregnancy, and intensive surveillance during and after pregnancy are essential to improve pregnancy outcome and ensure the best maternal and fetal prognosis.

Detection of an inherited genetic defect induce a physician’s reflection about family screening. Thrombophilia screening in relatives should be selective and performed after adolescence or before prescribing birth control pills, especially to young Index patient’s daughters. All other young family female members should be additionally evaluated for possible screening. The relatives should be informed that a genetic mutation is only one risk factor predisposing to venous thromboembolic disease. Not all patients with the same mutation will develop a thrombosis or PE or will become ill.

Index patient’s relatives undergo a targeted thrombophilia screening, i.e. just the detected defect should be ruled out. Degree of relationship, age, therapy, indication or contraindication for anticoagulation should be included in the evaluation before performing the screening. As indicated above, potential risk of false positive results and over-treatment should be kept as low as possible. Therefore, vitamin K-deficiency in young women, drugs with potential interactions with the tests, circadian variation of the coagulation factors should all be considered in the final evaluation [62]. All results of functional tests outside the normal reference ranges and suspect as a deficiency should be confirmed in a second blood sampling, at the earliest after one month.

First degree relatives should be informed—concerning the detected defect—about the relative increased risk of first VTE, transient additional risk factors, possible thromboembolic prophylaxis (Table 5). Evaluation of VTE risk should be regularly repeated and adapted based on age, on new risk factors or illness. Members of families with strong positive VTE’s history but negative thrombophilia screening require comprehensive information. Thus, transient risk factors should be avoided whenever possible and women should receive an alternative medication to estrogen-containing pills or devices.

If a thrombophilic variance is detected in a family member, the question arises how to proceed concerning prophylaxis. The first risk stratification of patients is based on the personal history. In addition, physical habitus, age, type of coagulation anomaly, type of mutation (heterozygous or homozygous), underlying disease and other risk factors should be taken into consideration. In these patients, we generally recommend to avoid immobilization and/or dehydration. Especially with varicose compression stockings in risk situations (immobilization, travel longer than 4 h, pregnancy, postoperatively) are recommended. In these risk situations we recommend a careful drug prophylaxis and in women we favor against the prescription of estrogen-containing preparations (Table 8).

If the family history is clearly strong positive and no laboratory thrombophilia is proved, the prophylactic measures are recommended as above. Even more, if the personal medical history is also positive for VTE.

The physiological adaptations of the body, the blood circulation and the coagulation during pregnancy increase the risk of thrombosis. Although the risk is influenced ante-partum especially by the BMI, age, number of births, varicosis and post-partum due to premature birth, cesarean section and hemorrhage, the VTE risk in women with hereditary thrombophilia and positive family history is especially high. Possible obstetric complications in the presence of thrombophilic defects are e.g. pre-eclampsia in antithrombin- or protein S deficiency or the fetal growth retardation in factor V Leiden and prothrombin gene G20210A mutation [81]. The assessment of the personal risk prior to the initiation of medication for thromboembolic event prophylaxis and regular checks during pregnancy are indicated for these patients. Start (24th week of gestation or earlier), dose and duration of prophylaxis are individual to decide. We recommend the prophylaxis with low molecular weight Heparins (LMWH), risk and weight-adapted (usually 75–100 IU/kg body weight/day), until the onset of labor pains. An interval of 12 h from the last LMWH low-dose is enough to carry out a spinal anesthesia. An interdisciplinary management of these patients with involvement of gynecologists, midwives, anesthesiologists and hematologists during pregnancy, at delivery and in the post-partum period is strongly recommended.

High-throughput sequencing methodology is now available and affordable for every-day genetics [82]. In the era of the GWAS it is possible, that genetic cohort analysis of pre-specified patients or healthy persons can reveal single polymorphisms, which alone or in combination are associated with thrombotic risk. Genetic risk scores or clustered panels of thrombotic genes with respect to this have already been published [34, 83, 84]. The benefit of such a wide genetic analysis, though, remains uncertain. Many of such gene candidates and their biological influence are at present unknown. The identification of variants of unknown significance (VUS) can be at present disturbing than helping. Moreover, the identification of variants, known to be associated to other diseases than thrombosis, such as the RUNX1 variation for leukemia or the aneuploidies can cause more problems than answer questions [84]. Should they be reported within the context of thrombophilia investigation or should they be silenced? Is there a risk for misinterpretation of the genetic results? How can we risk-stratify a VUS? These questions are still open, there is an urgent need for re-defining the indications and dimensions of extensive genetic testing.