When blood is collected from an arterial line it is necessary to discard the first 20 mL of blood to clear any heparin from the line before collecting the blood for coagulation tests
When collection is by vacuum tube, the coagulation tube should be collected second to avoid artefactual shortening of coagulation assays due to trauma of venesection
When blood is collected for an APTT or Anti-Xa Assay for control of heparin or low molecular weight heparin therapy, it is essential that the citrate tube is sent immediately to the laboratory | 
