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High levels of factor XI have been implicated as a risk factor for deep venous thrombosis and possibly cardiovascular disease; however, the relationship between elevated factor XI activity and stroke has yet to be established. We retrospectively evaluated factor XI activity, factor XI antigen, and high-sensitivity C-reactive protein (hs-CRP) values in samples from 65 patients with stroke, 13 with transient ischemic attack (TIA), and 17 with venous thrombosis, younger than 55 years with normal prothrombin and partial thromboplastin times who underwent evaluation for a hypercoagulable state. Factor XI activity levels were more than normal in 22% of patients with stroke or TIA and 18% of patients with venous thrombosis, producing odds ratios of 5.3 and 4.1 for stroke or TIA and venous thrombosis, respectively. Factor XI activity levels correlate with factor XI antigen levels by Deming regression analysis (slope, 1.3; R = 0.667) and a lack of correlation of both with hs-CRP suggests that factor XI is not an acute phase reactant. Our findings suggest an association between elevated factor XI activity and stroke.

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profiles may be different, the exposure to this dose of androstenedione may be similar. Unfortunately, the majority of publications to date that include data on the disposition of androstenedione do not detail changes in the AUCs of either androstenedione or testosterone as a measure of exposure. Assuming there is no large difference in steroid metabolic pathways between genders, then the difference in plasma androstenedione profiles observed may possibly be rationalized by differences in formulated products, but further investigations are required to support this supposition.In conclusion, the marketing of androstenedione as a dietary supplement should be a cause for concern because even a single administration of 100 mg produced supraphysiologic concentrations of plasma testosterone in healthy women. The exposure to testosterone would be expected to be repeated with daily administration of 100 mg of androstenedione over several weeks, but in our opinion, the risk of virilization precludes testing this hypothesis. Given the concern raised by healthcare professionals regarding the medical consequences of misuse of anabolic steroids, not least that of virilization (16 ) ( 1 ARUP Laboratories, Salt Lake City, UT 84108; 2 Departments of Medicine and Pathology, University of Utah Health Sciences Center, Salt Lake City, UT 84132; * address correspondence to this author at: Division of Hematology, University of Utah Health Science Center, 50 North Medical Dr., Salt Lake City, UT 84132; fax 801-585-5469, e-mail george.rodgers@hsc.utah.edu)The thrombin time (TT) assay is a core test in clinical laboratories that perform coagulation testing. This assay screens for abnormalities in the conversion of fibrinogen to fibrin. The time necessary for fibrinogen to clot is affected by hypofibrinogenemia, dysfibrinogenemia, and the presence of inhibitors of the fibrinogen-to-fibrin reaction (heparin, hirudin, fibrin degradation products, and paraproteins) (1 ).The TT is used primarily to evaluate plasma specimens with prolonged activated partial thromboplastin time (APTT) values and, to a lesser extent, prolonged prothrombin time (PT) values for heparin or other thrombin inhibitors. The test is also useful to detect quantitative and qualitative fibrinogen abnormalities. Important criteria for selecting a TT reagent are high sensitivity to heparin, sensitivity to hypofibrinogenemia, and acceptable precision. We compared five commercial TT reagents on our automated coagulation analyzer and evaluated their sensitivity to fibrinogen and heparin concentration, their precision, and their accuracy.Information on each of the five TT reagents evaluated is provided in Table 1 of the data supplement (available with the online version of this Technical Brief at http:// www.clinchem.org/content/vol49/issue1/). Each commercial reagent was reconstituted according to the manufacturer's instructions and used to measure TT in singleton measurements on the STA-R coagulation analyzer (Diagnostica Stago) according to the manufacturer's specifications ...

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