Thrombomodulin (TM) is an endothelial receptor for thrombin. The thrombin-thrombomodulin complex activates protein C in the anticoagulant pathway. Soluble TM is thought to be a marker for endothelial cell damage. We have evaluated the analytical performance of the HISCL TM test, a chemiluminescent enzyme immunoassay that measures soluble TM using biotinylated thrombomodulin monoclonal antibodies on Sysmex HISCL-2000i analyzer. Within-run coefficient of variation (CV) for control samples with low and high TM levels were 1.67% and 1.95% whereas between-run CVs for the control samples were 2.18% and 3.25% respectively. The assay showed excellent dilution linearity up to a TM level of 198 TU/mL with the lower limit of detection of 0.34 TU/mL. There was no effect of interfering substances on TM measurements. Results obtained on 362 patients showed that for those patients with a high TM level, C-reactive protein (CRP), fibrinogen (FIB), D-dimer, thrombin-antithrombin complex (TAT) and plasmin-α2 plasmin inhibitor complex (PIC) levels were significantly higher than in those patients with a normal TM level, and glomerular filtration rates (eGFR) were significantly lower than in those patients with a normal TM level. It was also observed that patients with high TM levels have significantly higher levels of von Willebrand factor antigen (vWFAg) and ristocetin cofactor activity (vWFRCo) which are associated with marked endothelial dysfunction. This study demonstrates that the HISCL TM test fulfils the analytical performance requirements for routine laboratory testing and an increased TM level detected is a useful indicator of endothelial dysfunction.