Reagent and method for assaying thrombin-antithrombin complex

1. A method for measuring (T)-antithrombin (AT) (TAT) complexes in a sample separated from a living body, comprising:

(a) performing a latex immunoagglutination reaction under an acidic condition of pH 5.8 to 6.6, comprising contacting the sample with a latex agglutination assay reagent wherein the latex agglutination assay reagent comprises:

(i) a first antibody bound to a first latex particle, wherein the first antibody binds to the antithrombin part of the TAT complex and recognizes the complex, wherein the first antibody has a reactivity to the TAT complex that is 100 to 50,000 times higher than the reactivity to from antithrombin, and (ii) a second antibody bound to a second latex particle wherein the second antibody binds to the thrombin part of the TAT complex and recognizes the complex; and

(b) measuring agglutination of latex particles formed by the reaction of the TAT complex, first antibody of (i) and the second antibody of (ii), thereby determining the amount of TAT complexes in the sample.

2. The method according to claim 1 , wherein said condition is pH of 6.0 to 6.4.

3. The method according to claim 1 , further comprising: contacting the sample with a first reagent comprising a buffer solution at a pH of 5.8 to 6.6 to form a mixture prior to step (a), and wherein performing the latex immunoagglutination reaction under an acidic condition of pH 5.8 to 6.6, comprises contacting the mixture comprising the sample and the first reagent with latex agglutination assay reagent.