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Specimen Quality

The accuracy of hemostasis laboratory tests depends on the quality of the specimen submitted. Specimens must be properly collected, labeled, stored, packaged, and transported to the laboratory. These instructions, when properly followed, ensure specimen integrity.


Preparing to Collect a Specimen

The specimen container must be properly identified with the patient's full name, medical record number, date and time of collection; and collector's initials. A properly completed request form, including a brief patient history, must accompany each specimen. Anticoagulant therapy such as heparin or Coumadin (warfarin) affects many test results and must be noted on the test request form. The ordering physician must sign the form.


Hemostasis Blood Specimen Collection

1.       Draw blood into a plastic blue top tube, which contains 3.2% (0.109 M) sodium citrate anticoagulant. Allow the tube to fill to the proper level, determined by the vacuum in the tube. Most tubes contain contain 0.3 mL anticoagulant and draw 2.7 mL of blood. A "short draw" yields grossly inaccurate results. When collecting with a butterfly unit, collect a discard tube first as the tubing delivers 0.5 mL of air.

2.       Immediately after collection, gently invert 6 times to mix. Do not shake. Transport to the laboratory immediately at room temperature. Do not transport on ice.

3.       Centrifuge the capped tube at 2500 xg for 10 minutes. Remember: "g" stands for g-force or relative centrifugal force (RCF), not RPM. RCF is used to calculate the correct RPM for individual centrifuges.

4.       Transfer plasma with a plastic pipette into a plastic centrifuge tube, cap and centrifuge an additional 10 minutes at 2500 xg to obtain platelet poor plasma, that is, plasma with a platelet count less than 10,000/uL. Specimens that are to be frozen and specimens for lupus anticoagulant and protein S activity testing must be platelet poor.

5.       Using care not to disturb the button at the bottom, transfer the plasma into another clean plastic tube using a plastic pipette. Seal the tube and label with patient name, identification number, and date and time of collection.

6.       The specimen must be tested within 4 hours of collection. If the assay cannot be completed within that time, it must be frozen at -70°C (step 7).

7.       Freeze the specimen immediately at -70°C. Specimens should not be frozen in an ordinary household freezer nor stored in a self-defrosting freezer as the continuous freeze-thaw cycle adversely affects specimen integrity.

8.       Send frozen specimens via overnight delivery on a minimum of 5 lbs. of dry ice. Specimens must remain frozen during transport.


Hematocrit Adjustment for Hemostasis Specimen

The ratio of whole blood to anticoagulant must be 9:1 for coagulation testing. If previous testing has revealed that the patient's hematocrit exceeds 55%, the amount of anticoagulant used should be adjusted according to the following formula:

C=1.85 x 10-3 x (100-HCT) x V
C= volume of 3.2% sodium citrate in mL
HCT= hematocrit in percent
V= volume of whole blood in mL

No adjustment is necessary for a low hematocrit.

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