The quantikine swine anti-thrombin receptor immunoassay is a 4.5 hour solid phase elisa designed to measure anti-thrombin receptor levels in cell culture supernates, serum, and plasma. It contains e. Coli-expressed recombinant swine anti-thrombin receptor and antibodies raised against recombinant swine anti-thrombin receptor. This immunoassay has been shown to accurately quantitate the recombinant factor. Results obtained using natural swine anti-thrombin receptor showed dose response curves that were parallel to the standard curves obtained using the recombinant quantikine kit standards. These results indicate that this kit can be used to determine relative mass values for natural swine anti-thrombin receptor