Effect of Calcium Ion on the Euglobulin Clot Lysis Time: Significant shortening by physiological concentration of calcium ion

Abstract

Euglobulin clot lysis time (ECLT) assay has been considered to be useful to assess the systemic fibrinolytic activity [1] [2]. ECLT is respected to show mainly the activity of tissue plasminogen activator (tPA), since antibody against tPA significantly prolonged ECLT. We have recently shown, however, that ECLT is primarily determined by the amounts of plasminogen activator inhibitor type 1 (PAI-1) due to the fact that ECLT inversely correlates with the concentration of PAI-1 whereas it did not have any meaningful correlation with tPA antigen level [3]. Taken together these results suggest that the activity of tPA either in plasma or in the euglobulin fraction is controlled by the balance of the concentrations of tPA and PAI-1 and that ECLT reflects the amounts of the active form of tPA which is not bound to PAI-l. We also recently showed that the addition of kaolin to ECLT (kaolin activated ECLT), in which the contact phase of both the coagulation and fibrinolysis is fully activated, significantly shortened regular ECLT, suggesting that intrinsic fibrinolytic pathway is not mainly involved in regular ECLT [3]. In this paper we report another pathway to enhance ECLT which is induced by the addition of physiological concentration of calcium ion. We believe it important because Ca²⁺ has been considered to work only to prolong fibrinolysis.