Specimen Requirements
Collection Instructions
Collect specimen in a blue top (citrate 3.2%) tube. Mix by inversion. Specimen should arrive at lab within 3 hours of collection; transport at room temperature. Alternatively, centrifuge, aliquot plasma into a plastic tube, and freeze the specimen within 4 hours of collection. Transport frozen specimen on dry ice. Collection of the blood through lines that have been previously flushed with heparin should be avoided. If the blood must be drawn through a VAD (vascular access device), the line should be flushed with 5 mL of saline and the first 5 mL of blood or six dead space volumes of the VAD discarded.
Rejection Criteria
Specimens will be rejected if not properly filled, clotted, grossly hemolyzed, or contaminated with heparin levels above 1.0 IU/ml. Test will be cancelled on patients receiving Anti-Xa other than Unfractioned heparin, and Anti-IIa anticoagulant therapies.
Contraindications
Plasma containing heparin levels greater than 1.0 IU/ml may give false positive results and should not be tested. This test is non-diagnostic in the setting of Low-molecular-weight heparin/ unfractionated heparin/direct oral anticoagulant use. This test is not indicated for inpatient evaluation of acute thrombosis.
Normal Volume
Full 2.7mL tube or 1mL plasma aliquot
Minimum Volume
Full 1.8mL tube or 1mL plasma aliquot
Storage Temperature
Room temperature for whole blood or frozen aliquot of citrated plasma