Partial Thromboplastin Time (aPTT/PTT)
Container/Tube Type:
Collection Information:
Two tube volumes are available; 2.7 mL Blue Sodium Citrate Tube or 1.8 mL Light Blue Sodium Citrate Tube.
Tube must be filled to a 1:9 ratio- see example of fill volumes below.
Question: How can I tell the 1.8 mL and 2.7 mL tubes apart?
Answer: The 1.8 mL tube has a light blue rubber stopper covered with a translucent shield with 1.8 mL on the bottom left of the label. The 2.7 mL tube has a light blue rubber stopper covered with a solid light blue shield with 2.7mL on the bottom left of the label.
Collection from a PICC line in which heparin has been infused is not recommended.
Transport Information:
Promptly after collection, the specimen is centrifuged to obtain platelet-poor plasma. The plasma is removed from the cells, placed in an aliquot tube and frozen.
Minimum Sample Volume: 
Question: What is the minimum volume of blood that should be collected into a BD Vacutainer sodium citrate tube?
Answer: BD tubes are designed to yield within ± 10% of the stated draw volume on the label. The minimum blood collected should be equal to the volume on the tube. Ex: 1.8 mL label = collect 1.8 mL of blood
Remarks:
3.2% buffered sodium citrate is the only acceptable anticoagulant concentration for this testing. Tube should be inverted several times immediately after collection, mixing blood and anticoagulant, to prevent clotting. Tube must be filled with appropriate volume to obtain the proper 9:1 ratio blood to anticoagulant-see tube label.
This test is used to monitor heparin therapy.
Unacceptable Conditions:
Clotted, Hemolyzed or Does not meet collection, storage or transport requirements
Stability Comments:
Whole Blood - Ambient: 4 hours unless on heparin therapy.
It is recommended that specimens be centrifuged and the platelet poor plasma be removed from the cells and frozen.
PTT testing can not be added on to a specimen that has exceeded the 4 hour specimen acceptability (or 2 hours for patients on heparin therapy.)
Platelet Poor Plasma
Centrifuge Specimen
Recommended centrifuge speed is 1500 x G for at least 15 minutes. Be careful that the tubes are evenly balanced when placing them into the centrifuge. When the centrifuge stops, carefully remove and rack tubes. Be aware that an unbalanced centrifugation, speed too slow, or centrifugation for too short of a spin time may all lead to an increase number of cells in the plasma which could contribute to a clotted specimen or erroneous results.
Remove Plasma
To remove plasma, start from the top, gently draw specimen into pipette as you go further down tube. Leaving approximately 0.5mL of plasma will insure that you do not disturb the buffy coat and cell layer.
Second Spin
Plasma separated from cells goes back into the centrifuge for a second spin. Balance and centrifuge the tubes. Failure to perform a second spin will result in plasma containing too many platelets which interfere with some coagulation testing and is a contributing factor for a clotted specimen.
Transfer Plasma to Aliquot Tubes
Pipette plasma from second spin tube into labeled aliquot tubes without disturbing the bottom 0.5mL.
Specimen Storage
Promptly freeze specimens after processing.
Stability
Refrigerated Stability:
Frozen Stability:
Platelet Poor Plasma - 14 days
Ambient Stability:
Platelet Poor Plasma - 4 hours
Patients on Heparin Therapy - Plasma acceptable for 2 hours