RT Book, Section A1 Laposata, Michael A1 McCaffrey, Peter SR Print(0) ID 1187001199 T1 Methods in Clinical Coagulation T2 Clinical Laboratory Methods: Atlas of Commonly Performed Tests YR 2022 FD 2022 PB McGraw Hill, LLC PP New York, NY SN 9781260470284 LK accessmedicine.mhmedical.com/content.aspx?aid=1187001199 RD 2024/03/29 AB A patient’s platelet-poor plasma (it is specifically plasma and not serum, as the process of clotting plasma to create serum consumes the coagulation factors) is placed in a testing chamber. For the PT assay, the specimen is mixed with thromboplastin and calcium. For the PTT assay, partial thromboplastin, an activator to initiate the clotting cascade, and calcium are added. The end point of the reaction is clot formation which may be detected optically, because the sample becomes more turbid with clotting, or mechanically, because clot formation reduces the ability of a magnet or other movable object added to move freely.