From Madan Verma:
Why are we allowed to add on a prothrombin time (PT) assay even 24 hours after collection? I was trying to find the factors’ half lives in vivo and wondering that factor VII has the shortest half life. Please explain. Can you please cite some literature regarding factor half lives? At http://uabcoag.net I found a summary, but it does not indicate these are in vivo or in vitro. Many-many thanks.
Hello, Madan Verma, and thank you for your question. The table on http://uabcoag.netis an adaptation of Table 45, page 632 of Fritsma MG, Fritsma GA. Chapter 40: Normal hemostasis and coagulation. In Rodak BF, Fritsma GA, Keohane EM. Hematology: Clinical Principles and Applications, 4th Edition, Elsevier Saunders, St. Louis, 2011. Factor VII’s in vivo plasma half-life is 6 hours, perhaps owing to its tendency to become activated and consumed as it binds tissue factor. In vitro, however, factor VII is stable, accounting for the stability of the PT, as documented in Adcock D, Kressin D, Marlar RA. The effect of time and temperature variables on routine coagulation tests. Blood Coagul Fibrinolysis 1998;9: 463-470. The Adcock publication is referenced in Clinical and Laboratory Standards Institute: Collection, transport, and processing of blood specimens for testing plasma-based coagulation assays: approved guideline, ed 5, CLSI Document H21-A5, Wayne, PA, 2008.
Contrast the PT to the partial thromboplastin time (PTT), which Adcock illustrates is stable for only four hours in vitro. The PTT depends upon an intact intrinsic coagulation pathway, which includes factor VIII, whose in vivo half-life is 12 hours but whose in vitroactivity deteriorates by approximately 10% per hour. Factor VIII’s deterioration accounts for the progressive lengthening of the PTT during storage.
By the way, specimens for PT and PTT should be stored at room temperature, 18°C–24°C. Refrigeration activates factor VII and platelets and causes large VWF multimers to precipitate, whereas storage above 24°C hastens factor VIII deterioration. Geo
Please clarify:
After collection in a blue top, how long ca
Please clarify:
After collection in a blue top, how long can samples for PT sit unspun at room temperature, also; samples for APTT sit unspun at room temperature? (hospital lab) Thank you.
Hello, the 24-hour limit applies to specimens collected for PT either spun or unspun, and the 4-hour limit applies to the PTT with the specimen unspun, unless the PTT was collected to monitor unfractionated heparin, then it must be separated and tested within one hour.
Some answers appear in Woodhams B, Stability of coagulation
Some answers appear in Woodhams B, Stability of coagulation proteins in frozen plasma. Blood Coag and Fibrinolysis 2001;12:229-236, Sincerely yours
What would your recommendation be for the following scenario
What would your recommendation be for the following scenario: Blue top is submitted to the lab with no orders. We usually spin the sample down and have started leaving it out at room temp for 4 hours, then freezing. We only do prothrombin time (PT) and partial thromboplastin time (PTT). We only have a -20 degree freezer.
Note added from George on 4/15/11: Assuming the tube is properly labeled, I recommend you place the plasma in the freezer within the first hour after collection. If the specimen was collected to monitor unfractionated heparin, the heparin begins to be neutralized by the release of platelet factor 4 with a measurable shortening of the PTT after the first hour. The -20 freezer will freeze the specimen rapidly enough to prevent heparin neutralization, and the specimen is good for up to two weeks, provided the freezer does not have a defrost cycle.
Hello, jpcarrol, no, specimens for PT or PTT should be store
Hello, jpcarrol, no, specimens for PT or PTT should be stored at room temperature (see the specifications in CLSI H21-A5). Never refrigerate or place on ice. If the PT cannot be assayed within 24 hours or the PTT within 4, you should centrifuge to produce platelet-poor plasma, then aliquot and freeze until ready to assay. Geo.
Now I’m confused. I thought specimens for PT/PTT should be
Now I’m confused. I thought specimens for PT/PTT should be refrigerated or frozen, or is that only if it will be for a longer time period?