Heterogeneous immunoassay using a precipitable solid phase

A method for the heterogeneous immunochemical detection and quantitation of an analyte in a sample of a biological fluid, which method includes the following steps

• a) immobilizing a first, unlabeled specific binding partner for the analyte on a pipettable, particulate solid phase,
• b) adding the sample to the immobilized, unlabeled specific binding partner,
• c) carrying out a first incubation of the reaction mixture,
• d) adding a defined quantity of a labeled, specific detection substance,
• e) carrying out a second incubation of the reaction mixture,
• f) precipitating the solid phase by adding at least one substance from the group which comprises the following precipitation substances:
• i) a second specific binding partner which is directed against the solid phase,
• ii) a second specific binding partner which is directed against an anchoring substance which is immobilized on the solid phase,
• where the second specific binding partners are preferably of a species which is different from that of the first unlabeled specific binding partner,
• g) centrifuging the reaction mixture,
• h) transferring at least some of the supernatant arising in step g) to a measuring chamber,
• l) starting a detection reaction in the measuring chamber, and
• j) determining the analyte concentration from the detection reaction.