<prompt> Which of the following statements are true about estimation of prothrombin time PT?Immediate refrigeration to preserve factor bilityPlatelet-rich plasma is essentialDone preferably within 2 hours of collectionUtilises Kaolin  <response>: In coagulation studies: Most routine coagulation investigations are performed on platelet-poor plasma PPP. The sample should be kept at room temperature if it is to be used for PT tests, lupus anticoagulant LAC or factor VII assays and it should be kept at 4 degC for other assays. The testing should preferably be completed within 2 h of collection. Coagulation studies are of 2 types: PT -- Thromboplastin is used aPTT -- Kaolinsilica is used Anticoagulant of choice for this study is 3.2 trisodium citrate. Ratio of blood sample to anti-coagulant is 9:1. 