Sample conditions determine the ability of thrombin generation parameters to identify bleeding phenotype in FXI deficiency

Abstract

Key Points• When contact activation is inhibited, Factor XI:C levels only correlate with thrombin generation if platelets are present.• Thrombin generation measured in platelet-rich plasma with contact activation inhibition identifies bleeding phenotype in FXI deficiency.Individuals with Factor XI (FXI) deficiency have a variable bleeding tendency that does not correlate with FXI:C levels or genotype. Comparing a range of sample conditions, we tested whether the thrombin generation assay (TGA) could discriminate between control subjects (n 5 50) and FXI-deficient individuals (n 5 97), and between those with bleeding tendency (n 5 50) and without (n 5 24). The comparison used platelet-rich plasma (PRP) and platelet-poor plasma (PPP), either with or without corn trypsin inhibitor (CTI) to prevent contact activation, over a range of tissue factor (TF) concentrations. When contact activation was inhibited and platelets were absent, FXI:C levels did not correlate with thrombin generation parameters, and control and FXI-deficient individuals were not distinguished. In all other sample types, the best discrimination was obtained using TF 0.5 pM and assay measures: endogenous thrombin potential (ETP) and peak height. We showed that although a number of conditions could distinguish differences between the groups tested, TGA measured in PRP with CTI best differentiated between bleeders and nonbleeders. These measures provided high sensitivity and specificity (peak height receiver operating characteristic [ROC] area under the curve [AUC] 5 0.9362; P < .0001) (ETP ROC AUC 5 0.9362; P < .0001). We conclude that by using sample conditions directed to test specific pathways of FXI activation, the TGA can identify bleeding phenotype in FXI deficiency. (Blood. 2015;126(3):397-405)

Elevated thrombin generation in patients with congenital disorder of glycosylation and combined coagulation factor deficiencies

“…Last, the TGA is reportedly suitable for detecting an AT deficiency and seems less influenced by FXI. TGA is more sensitive to FXI in the presence of platelets and when the tissue factor concentration is low . In our conditions, when TGA is assessed in platelet‐poor plasma with high tissue factor concentration (5 pmol/L), the thrombin generation profile is primarily driven by antithrombin deficiency.…”

The hemostatic role of factor XI

“…In contrast, a recent study demonstrated that a thrombin generation assay in platelet-rich plasma (PRP) in which the contact pathway was inhibited while the extrinsic pathway was activated via TF was able to successfully identify which FXI-deficient patients demonstrated a bleeding phenotype [16]. These differing results suggest that FXI does not play a role hemostasis via the contact pathway but that FXI can initiate coagulation via the extrinsic pathway in the presence of TF and platelets.…”

Why factor XI deficiency is a clinical concern

“…Curiously, this discriminatory ability was lost if TF or CTI was added, indicating fXIa generated by fXIIa was being measured. In contrast, Pike et al noted significant differences in thrombin generation between fXI deficient bleeders and non-bleeders in platelet-rich plasma with 0.5 pM TF and CTI, [48]. Here, the inclusion of platelets may have provided a co-factor for fXI activation by thrombin in the form of polyphosphate [27–29].…”