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Unfractionated heparin (UFH) is the main anticoagulant used in intensive care unit. The anticoagulant effect is monitored by activated partial thrombin time (aPTT) and anti-Xa activity (anti-Xa) measurement. However, delayed centrifugation induces platelet factor 4 (PF4) release and anti-Xa decrease. Several studies have concluded that aPTT and anti-Xa measurement should be performed within 2 h in citrated anticoagulant but may be delayed longer in Citrate Theophylline Adenosine and Dypiridamol (CTAD) anticoagulant. The objective of this study was to compare the stability of both aPTT and anti-Xa in citrate and CTAD samples, and to determine the effect of delayed centrifugation on both aPTT, anti-Xa results, and PF4 release in citrate samples only. aPTT and anti-Xa were measured in citrate and CTAD anticoagulant samples from 93 patients. Delayed centrifugation was performed in citrate samples from 31 additional patients, with hourly aPTT and anti-Xa measurement from 1 to 6 h. In 14 of these last patients, PF4 release was also evaluated with Human CXCL4/PF4 Quantikine ELISA Kit. We observed a significant correlation between citrate and CTAD anticoagulant for aPTT (r2 = 0.94) and anti-Xa (r2 = 0.95). With Bland–Altman correlation, a minor bias was observed for anti-Xa (− 0.025 ± 0.041). Delayed centrifugation in citrated anticoagulant showed an excellent concordance from 1 to 4 h for aPTT (− 4.0 ± 5.3 s) and anti-Xa (1.10−9 ± 0.058 UI/ml) measurements. Moreover, PF4 release was not different between 1 h (31.5 ± 14.7 ng/ml) and 4 h (33.8 ± 11.8 ng/ml). We have demonstrated that anti-Xa measurement for unfractionated heparin should be done 4 h in citrated plasma and that CTAD was not better than citrate. However, these initial findings require confirmation using other aPTT and calibrated anti-Xa assays.

Factor V Leiden (FVL) mutation is the most common genetic risk factor for venous thromboembolism. In families with a history of thrombosis, FVL can be present in 18%. Thrombin generation test is commonly used as an evaluation tool of thrombotic risk. The objective of this study was to evaluate the thrombogenic potential of FVL in asymptomatic carriers and in patients with personal or familial history of thrombosis. This was a retrospective single center study including 160 patients. Among them, 43 had personal history of thrombosis and 117 had familial history of thrombosis. Thrombin generation (TG) was realized in frozen platelet poor plasma with 1 pM of tissue factor and 4 µM of phospholipid. FVL mutation was associated with a global increase of TG. No difference was observed between patients with provoked thrombosis and patients with first-degree familial history of thrombosis (endogenous thrombin potential (ETP): 1501.0 ± 316.4 nM min and thrombin peak: 253.4 ± 71.5 nM vs. 1520.4 ± 283.8 nM min and 268.6 ± 68.0 nM). An increase of TG was observed in patients with unprovoked thrombosis (n = 23) and in patients with provoked thrombosis (n = 20) (ETP: 1819.5 ± 319.8 nM min and peak: 332.3 ± 55.8 nM). In the unprovoked thrombosis group, patients with a pulmonary embolism had a higher ETP than patients with deep vein thrombosis (DVT) (2036 ± 343 nM min vs. 1707 ± 261 nM min). With a predictive score formula (s = 0.1315 × Age + 0.0105 × ETP) with a threshold of 22.1 as risk to develop an unprovoked thrombosis among patients with second-degree familial history. The results of our analysis suggest that measurement of thrombin generation in patients with FVL mutation may identify subjects with an increased risk of unprovoked thrombosis. Further studies are needed to examine the usefulness of predicting thrombotic presentation in asymptomatic carriers.