Small clots or fibrin strands indicate an activated sample and must be recollected. Processing and Handling Processing and handling are other important variables to consider. This will eliminate the potential for the release of platelet factor IV and phospholipids, which inhibits heparin and may affect the monitoring of heparin. It is recommended that samples be spun at 1,500g for a minimum of 15 minutes at room temperature. However, all centrifuges are different, so each laboratory should evaluate its own centrifuge's ability to obtain platelet poor plasma.
Many laboratories recommend a double spin technique to achieve platelet poor plasma.
These guidelines call for the sample for PT testing to be stored uncentrifuged or centrifuged with plasma on top of cells, at room temperature or refrigerated for testing within 24 hours of collection. The aPTT sample with no therapeutic heparin present can be stored under the same conditions as the PT sample, but should be tested within four hours of collection. Samples containing therapeutic heparin for aPTT testing should be centrifuged within one hour of collection and tested within four hours. All other coagulation assays should be spun within one hour and tested within four hours of collection. If this isn't possible, the plasma should be aliquoted into plastic tubes with secure caps and frozen.