Specimens cannot be analysed or re-analysed greater than 2 hours after collection.
When the collection is by vacuum tube,the coagulation tube should be collected second to avoid artefactual shortening of coagulation assays due to the trauma of venesection. When syringes are used, have ready two plastic syringes. A butterfly needle may be used. Withdraw 5 mL blood into the first syringe and discard the syringe (or use it for other tests). With the second syringe, withdraw the required amount of blood for the coagulation tests. When blood is collected from an arterial line it is necessary to discard the first 20mL of blood to clear any heparin from the line before collecting the blood for coagulation tests.