Methods of determining endogenous thrombin potential (ETP) and thrombin substrates for use in said methods

A method for determining the ETP of a sample said sample comprising anticoagulant resulting in a total anticoagulant activity of or equivalent to 0.0-0.25 U ISH/ml said method comprising using a thrombin substrate or a salt of the substrate that is soluble in the sample in the determination of the ETP of said sample, wherein said thrombin substrate is selected from the group consisting of dipeptide thrombin substrates including the formula P-Val-Xaa-S, wherein

• P is an amino protective group, said amino protective group is non-aromatic, polar, and fits in the aryl binding pocket of thrombin,
• Val is a valine residue attached via a peptide bond to Xaa,
• Xaa is an amino acid residue comprising a terminal guanidino group or ureido group separated by at least 2 carbon atoms from the peptide backbone, said amino acid residue being attached to S,
• S is a signal group such as a that can be enzymatically hydrolyzed with the proviso that the substrate is not CH3O—CO—CH2—CO-L-Val-Arg-p-nitroanilide or H-Val-Arg-p-nitroanilide and a thrombin substrate of the formula H-Glu-Gly-Gly-Val-Arg-p-nitroanilide (SEQ ID NO:
• 3) or a salt thereof.

A dipeptide thrombin substrate comprising the formula P-Val-Xaa-S, wherein

• P is an amino protective group,
• said amino protective group is non aromatic, polar, and fits in the aryl binding pocket of thrombin,
• Val is a valine residue attached via a peptide bond to Xaa,
• Xaa is an amino acid residue comprising a terminal guanidino group or ureido group separated by at least 2 carbon atoms from the peptide backbone, said amino acid residue being attached to S, and
• S is a signal group that can be enzymatically hydrolyzed with the proviso that the substrate is not CH3O—CO—CH2—CO-L-Val-Arg-p-nitroanilide or H-Val-Arg-p-nitroanilide.