Young & Thompson
Method of determining the heparin content
 In a method of determining heparin content, a known amount of thrombin (FIIa) or activated coagulation factor X (FXa) is added to a mixture which comprises a known concentration of chromogenic substrate (S), a known concentration of antithrombin (AT) and a sample having an unknown heparin concentration. The amount of FIIa or FXa is chosen such that at most 20%, of the S present is reacted during the period which the AT needs to deactivate all the FIIa or FXa present. The final concentration of the reacted chromogenic substrate p-nitroanilide ([pNA].sub.final) is determined after completion of the reactions, and the [pNA].sub.final is used to determine the rate constant (k.sub.dec) of the reaction of FIIa or FXa with AT using the relationship: ##EQU1## The heparin concentration in the sample can then be determined using the value of k.sub.dec from a predetermined calibration curve of k.sub.dec against heparin concentration. 
Universiteit Maastricht
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Y10S Y10S G01N C12Q G01N G01N Y10S G01N C12Q
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Hendrik Coenraad Robert Johan
Hemker Wagenvoord