Laboratory assays were performed in batch with each participant's serial samples analyzed in the same run. D-dimer, von Willebrand factor and antithrombin were measured using immuno-turbidometric assays on the STA-R analyzer (Liatest D-Di, Liatest vWF, Liatest ATIII, Diagnostica Stago, Parsippany, NJ) with coefficients of variation (CVs) of 3.0%, 3.85%, and 4.0-8.0% respectively. Factor VIII was determined by measuring the clotting time of the sample in factor VIII deficient plasma (STA-Deficient VIII; Diagnostica Stago, Parsippany, NJ) with a CV of 3.5%. Free and total protein S were measured by immunoassay (Asserachrom Free and Total Protein S, Diagnostica Stago, Parsippany, NJ) with CVs of 14.0% and 4.0% respectively. Fibrinogen and C-reactive protein were measured by immunonephelometry using the BNII instrument (N Antiserum to Human Fibrinogen, N High Sensitivity CRP, Dade-Behring, Deerfield, IL) with CVs of 2.3-4% and 2.6% respectively.