Method for measuring cystatin C in human body fluid

A method for measuring cystatin C in a human body fluid, comprising:

• (1) contacting a human body fluid with (a) first insoluble carrier particles coated with a first anti-human cystatin C monoclonal antibody which has affinity for cystatin C and (b) second insoluble carrier particles coated with a second anti-human cystatin C monoclonal antibody which has affinity for cystatin C,
• wherein
• the first anti-human cystatin C monoclonal antibody has an affinity for cystatin C that is higher than the second anti-human cystatin C monoclonal antibody,
• the first anti-human cystatin C monoclonal antibody has a dissociation constant of less than 1 nM,
• the second anti-human cystatin C monoclonal antibody on the second insoluble carrier particles recognizes an epitope of cystatin C that is different from the epitope recognized by the first anti-human cystatin C monoclonal antibody on the first insoluble carrier particles,
• wherein the dissociation constant of the second anti-human cystatin C monoclonal antibody divided by the dissociation constant of the first anti-human cystatin C monoclonal antibody is two or greater,
• the first insoluble carrier particles are coated with from 1% to less than 4% by weight of the first anti-human cystatin C monoclonal antibody, and
• the second insoluble carrier particles are coated with from 1% to less than 4% weight of the second anti-human cystatin C monoclonal antibody,
• (2) measuring the amount of cystatin C bound to the first insoluble carrier particles and the second insoluble carrier particles, and
• (3) correlating the amount of cystatin C bound to the first insoluble carrier particles and the second insoluble carrier particles with the amount of cystatin C in the human body fluid.