Full Length ArticleAssessment of two contact activation reagents for the diagnosis of congenital factor XI deficiency
Introduction
Activated partial thromboplastin time (APTT) is a global coagulation test that has been used during the last 50 years as a standard screening test in clinical laboratories throughout the world [1]. APTT levels are considered to reflect global coagulation activity. This test cumulatively explores factors belonging to the classic intrinsic (FXII, FXI, FIX, and FVIII) or common (FII, FV and fibrinogen) coagulation cascade. Factor XII is a known determinant of APTT. Polymorphism rs1801020, which has been associated with FXII levels, showed a highly significant association with APTT in normal population and case-control cohort of thrombosis [2], [3]. Besides its sensitivity toward variation levels of these coagulation factors, APTT is also associated with age, gender, estrogen therapy, and obesity [4].
Generally, coagulopathies involving deficiencies in the intrinsic pathway are evaluated widely by APTT. Prolonged APTT is an indicator of deficiencies of factors involved the intrinsic pathway [5], [6]. Numerous reagent systems for performing the APTT assay are commercially available. However, when the deficiency is mild, these assays vary in their sensitivity to clotting factor deficiencies.
FXI is a plasma serine protease zymogen of hepatic synthesis with a key role in bridging the initiation phase and the amplification phase of blood coagulation in vivo [7], [8]. FXI deficiency originally called haemophilia C, however yields mild bleeding tendency and, in turn, has significant protective effects from thrombotic diseases [9], [10], [11]. FXI deficiency has been considered a rare disorder and is usually diagnosed by prolonged APTT and confirmed by coagulation assays (FXI:C < 70%). Nevertheless, current reports suggest that this disorder is present worldwide in many populations and may be underestimated [12], [13], [14].
Sensitive and reliable methods to detect FXI deficiency and quantify FXI levels are required. In this study, using a large cohort of subjects with congenital FXI deficiency caused by 11 different mutations, we evaluated two assays for their ability to detect deficiencies of FXI, particularly mild deficiencies. Moreover, two commercially available contact activator reagents were compared, one based on ellagic acid and one based on silica.
Section snippets
Study subjects
The study included 140 subjects (77 male and 63 female donors varying in age from 5 to 88 years) from the Spanish Yecla-study [15], with congenital FXI deficiency characterized biochemically, functionally and molecularly. Briefly, during 20 years, 324,764 APTT tests from 51,366 hospital in- patients/out-patients were screened, selecting 1700 patients with an APTT ratio > 1.3 using SynthASil for further studies. Determination of FXI coagulation activity (FXI:C) in 173 patients with replicated and
Overall results
Table 3 shows a summary of all the results of APTT and FXI:C obtained in FXI deficiency patients analyzed by using two activators of the contact phase.
The silica-based reagent rendered significantly prolonged APTT times but lower APTT ratio than the ellagic acid-based reagent (Table 3). FXI:C values were significantly lower when determined with silica than when using ellagic acid.
Severe FXI deficiency (homozygous or compound heterozygous) largely prolonged APTT times and increased APTT ratios
Discussion
FXI deficiency has been considered a rare disease except for some specific populations. Thus among Ashkenazy Jews, FXI deficiency may be present in up to 8% of the population [8], [20]. However, a recent study evaluating available whole exome sequencing from different populations found a frequency higher than expected of pathogenic mutations leading to FXI deficiency [21]. This apparent contradiction may be explained by two reasons: 1) current diagnostic methods for FXI screening fail to
Conclusions
Moderate FXI deficiency, particularly CRM +, might be underestimated by the limitations of current diagnostic methods. APTT has particularly low sensitivity for FXI diagnosis as it is influenced by FXII levels (determined by a common F12 SNP), by FXI:C levels and by the activator of the contact phase. Our results suggests that the best screening method for FXI deficiency is FXI:C using silica.
Funding
This work was supported by PI15/00079; CB15/00055 (ISCIII and FEDER); and 19873/GERM/15 (Fundación Séneca). SS-A is the recipient of the Research Fellowship from the Spanish Society of Hematology and Hemotherapy (SEHH). MEM holds a fellowship from Fundación Española de Trombosis y Hemostasia (FETH).
Acknowledgments
This research was supported by Izasa Scientific/A WerfenLife Company. The authors are thankful to Alberto Lopez and Josep Garcia for assistance and the provided expertise that greatly assisted the research.
Authorship
S.S-A., J.E., M.E.M-B., J.C., V.R. and V.V. collected patients and clinical data, designed research, analyzed the data and wrote the paper. A.M. and C.A. performed genetic and biochemical experiments.
Conflict of interest
Authors have no conflict of interest.
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