The utility of thrombophilia testing

Thrombophilia Screening: Not So Straightforward

Although inherited thrombophilias are lifelong risk factors for a first thrombotic episode, progression to thrombosis is multifactorial and not all individuals with inherited thrombophilia develop thrombosis in their lifetimes. Consequently, indiscriminate screening in patients with idiopathic thrombosis is not recommended, since presence of a thrombophilia does not necessarily predict recurrence or influence management, and testing should be selective. It follows that a decision to undertake laboratory detection of thrombophilia should be aligned with a concerted effort to identify any significant abnormalities, because it will inform patient management. Deficiencies of antithrombin and protein C are rare and usually determined using phenotypic assays assessing biological activities, whereas protein S deficiency (also rare) is commonly detected with antigenic assays for the free form of protein S since available activity assays are considered to lack specificity. In each case, no single phenotypic assay is capable of detecting every deficiency, because the various mutations express different molecular characteristics, rendering thrombophilia screening repertoires employing one assay per potential deficiency, of limited effectiveness. Activated protein C resistance (APCR) is more common than discrete deficiencies of antithrombin, protein C, and protein S and also often detected initially with phenotypic assays; however, some centres perform only genetic analysis for factor V Leiden, as this is responsible for most cases of hereditary APCR, accepting that acquired APCR and rare F5 mutations conferring APCR will go undetected if only factor V Leiden is evaluated. All phenotypic assays have interferences and limitations, which must be factored into decisions about if, and when, to test, and be given consideration in the laboratory during assay performance and interpretation. This review looks in detail at performance and limitations of routine phenotypic thrombophilia assays.

Recent advances in laboratory hematology reflected by a decade of CCLM publications

On the occasion of the 60th anniversary of Clinical Chemistry and Laboratory Medicine (CCLM) we present a review of recent developments in the discipline of laboratory hematology as these are reflected by papers published in CCLM in the period 2012–2022. Since data on CCLM publications from 1963 to 2012 are also available, we were able to make a comparison between the two periods. This interestingly revealed that the share of laboratory hematology papers has steadily increased and reached now 16% of all papers published in CCLM. It also became evident that blood coagulation and fibrinolysis, erythrocytes, platelets and instrument and method evaluation constituted the ‘hottest’ topics with regard to number of publications. Some traditional, characteristic CCLM categories like reference intervals, standardization and harmonization, were more stable and probably will remain so in the future. With the advent of important newer topics, like new coagulation assays and drugs and cell population data generated by hematology analyzers, laboratory hematology is anticipated to remain a significant discipline in CCLM publications.

Prevalence of rare F5 variants in general population from Bosnia and Herzegovina

Human gene F5, encoding coagulation factor V, was previously reported to be highly polymorphic. Apart from FV Leiden, several other rare variants have been detected in clinical practice and associated with thrombotic events, especially in cases when patient's phenotype and FV Leiden genotype were not in agreement. In this study, the prevalence of 17 rare F5 variants has been studied on a sample of 130 healthy adult individuals from the general Bosnian-Herzegovinian population. DNA was isolated from buccal swab samples, while genotyping was performed using MALDI-TOF MS method. The results have shown that Asp2194Gly and Met2120Thr are polymorphic in the study population with minor allele frequencies of 0.077 and 0.073, respectively. Additionally, these two variants were mutually exclusive with FV Leiden and none of them was positively associated with participants' family history of cardiovascular or cerebrovascular diseases. While the obtained results are in agreement with previously reported data for the general Caucasian populations, it is worth noting that only two rare F5 variants were detected in the study population, albeit at considerable frequencies. Still, scientific information on rare F5 variants is rather scarce and further studies aiming to assess functional importance of these variants, as well as their role as prothrombotic factors are necessary.

Danger of false negative (exclusion) or false positive (diagnosis) for ‘congenital thrombophilia’ in the age of anticoagulants

Background

Most guidelines and experts recommend against performance of thrombophilia testing in general, and specifically against testing patients on pharmacological anticoagulants, due to substantially increased risk of false positive identification. For example, vitamin K antagonist (VKA) therapy affects protein C (PC) and protein S (PS), as well as some clotting assays (e.g. as used to investigate activated PC resistance [APCR]). Although heparin may also affect clotting assays, most commercial methods contain neutralisers to make them ‘insensitive’ to therapeutic levels. Direct oral anticoagulants (DOACs) also affect a wide variety of thrombophilia assays, although most reported data has employed artificial in vitro spiked samples.

Methods

In the current report, data from our facility for the past 2.5 years has been assessed for all ‘congenital thrombophilia’ related tests, as evaluated against patient anticoagulant status. We processed 10,571 ‘thrombophilia’ related test requests, including antithrombin (AT; n=3470), PC (n=3569), PS (n=3585), APCR (n=2359), factor V Leiden (FVL; n=2659), and prothrombin gene mutation (PGM; n=2103).

Results

As expected, VKA therapy affected PC and PS, and despite manufacturer claims, also APCR. Most assays, as suggested by manufacturers, were largely resistant to heparin therapy. DOACs’ use was associated with falsely low APCR ratios (i.e. FVL-like effect) and somewhat unexpectedly, anti-Xa agents apixaban and rivaroxaban were also associated with lower AT and higher PS values.

Conclusions

It is concluded that ex-vivo data appears to confirm the potential for both false positive and false negative ‘thrombophilia’ events in patients on anticoagulant (including DOAC) treatment.

Combined Thrombophilia in a Young Male Presenting as Life Threatening Pulmonary Embolism

Combined hereditary thrombophilia is an uncommon entity associated with higher risk of early onset thrombosis. We report a case of 39-year-old male with combined deficiency of natural anticoagulants (protein C, S and anti thrombin) along with hyper homocystenemia and factor V Leiden mutation, presenting with life threatening bilateral pulmonary embolism. The clinical implications of combined thrombophilia are also discussed.

Issues in the Diagnosis and Management of Hereditary Antithrombin Deficiency

Objective: To review insights gained in the past several years about hereditary antithrombin (AT) deficiency and to outline approaches to the management of patients with AT deficiency in the acute and chronic settings. Data Sources: An extensive literature search of Scopus (January 2008-April 2016) was performed for the terms congenital antithrombin deficiency, inherited antithrombin deficiency, or hereditary antithrombin deficiency. Additional references were identified by reviewing literature citations. Study Selection: All relevant English-language case reports, reviews, clinical studies, meeting abstracts, and book chapters assessing hereditary AT deficiency were included. Data Synthesis: AT deficiency significantly increases the risk of venous thromboembolism (VTE). The risk of VTE is particularly high during pregnancy, the postpartum period, and following major surgery. Effective clinical management includes determination of the appropriate type and duration of antithrombotic therapy (ie, AT replacement for acute situations) while minimizing the risk of bleeding. For persons newly diagnosed with AT deficiency, age, lifestyle, concurrent medical conditions, family history, and personal treatment preferences can be used to individualize patient management. Patients should be informed of the risks associated with hormonal therapy, pregnancy, surgical procedures, and immobility, which further increase the risk of VTE in patients with AT deficiency. Conclusion: AT deficiency poses the highest risk for VTE among the hereditary thrombophilias, often requiring long-term anticoagulation. Undertaking an evaluation for hereditary thrombophilia is controversial; however, a diagnosis of VTE in association with AT deficiency can have management implications. An important treatment option for patients with this disorder in high-risk situations is AT concentrate.