Method of reducing interferences in assays

An assay for detecting the presence of an analyte of interest in a test sample comprising the steps of:

• forming a reaction mixture by combining in an assay medium:
• (I) an assay system comprising a first binding member, a second binding member, a spacer member intermediate between the members, a first binding partner and a second binding partner, the first binding member capable of binding to the first binding partner, the first binding partner capable of binding to the analyte, the second binding member capable of binding to the second binding partner, the second binding partner aiding detection of either bound or unbound analyte in the reaction mixture;
• (ii) a test sample containing the analyte and heparin as an interfering substance that is capable of interfering with the assay by interacting with the second binding partner, and
• (iii) an additional mount of the heparin in a quantity effective to substantially mask the effect of the interfering substance in the test sample, wherein the additional amount of heparin is between about 40 units to about 90 units, and wherein the additional amount of heparin is in an effective quantity such that substantially all of the second binding partners in the reaction mixture are non-specifically bound to the interfering substance heparin:
• b. incubating the reaction mixture under conditions sufficient to allow the formation of a complex between the analyte and the first binding partner, and
• c. determining the presence of the analyte in the test sample by measuring the extent of any formation of the complex, the extent being proportional to the concentration of the analyte in the sample.

A test kit for detecting the presence of an analyte of interest in a test sample, the test sample containing an interfering substance that is capable of interfering with the assay, the test kit comprising at least one container containing the following components which can be partially or completely pre-combined or uncombined;

• a. an assay medium;
• b. a first binding member capable of binding to a first binding partner for the analyte;
• c. the first binding partner capable of binding to the analyte;
• d. a second binding member capable of binding to a second binding partner;
• e. the second binding partner aiding detection of either bound or unbound analyte in the reaction mixture, wherein the interfering substance in the test sample is heparin and is capable of interfering with the assay by interacting with the second binding partner, and
• f. an additional amount of heparin in a quantity effective to substantially mask the effect of the interfering substance in the test sample and wherein the additional amount of heparin is in an effective quantity such that substantially all of the second binding partners in the reaction mixture are non-specifically bound to the interfering substance heparin.