Hemostasis and Thrombosis

Hemostasis and Thrombosis Laboratory offers diagnostic testing for bleeding and thrombotic conditions. Open Monday through Friday, 8:00am to 4:30pm, the laboratory may be reached directly at 503 494-7383. Urgent work outside these times must be cleared by the Laboratory Medicine Resident on call. 

Specimen collection, processing, storage, and shipping are critical to obtain valid results for hemostasis tests. Adhere tightly to the instructions below to obtain accurate results.

Drawing samples

  • Collect specimens by peripheral venipuncture using a blood collection system that uses a straight needle; winged devices are acceptable especially in children, however small gauge needles of 25 or smaller may induce hemolysis.
  • Draw blood into siliconized evacuated tubes or plastic syringes containing buffered sodium citrate anticoagulant (light blue top tubes). If using a plastic syringe, it must have a non-activating surface such as polypropylene, and the sample must be added to the appropriate volume of anticoagulant within 1 minute of collection.
  • Evacuated tubes must fill by vacuum completely to the line on the tube.
  • Immediately after filling, mix tubes gently by 3 to 6 complete end-over-end inversions. Do not shake or mix vigorously.
  • Do not use the first tube/syringe for hemostasis samples. Some studies suggest that the first tube may contain tissue factor, which will cause activation of coagulation.      
  • The venipuncture must not be traumatic or slow flowing; avoid leaving the tourniquet on for an extended time.       
  • Unacceptable specimens include those that are clotted, collected in the wrong anticoagulant, collected with an inappropriate blood to anticoagulant ratio (i.e. under/overfilled tubes), and mislabeled or unlabeled specimens.


  • Process samples immediately, leaving samples capped until they are aliquoted.
  • Before centrifugation, check the whole blood specimen for gross clot formation be either gentle inversion and observation, or removing the cap and inserting and then removing two wooden sticks to detect the presence of a clot.
  • To obtain a platelet poor plasma sample, centrifuge at a minimum of 2000 x g for 20 minutes, in a refrigerated centrifuge, if available.  Alternative protocols are acceptable if the plasma platelet count is less than 10,000/uL. Do not filter the plasma to remove platelets, as filtering will remove high molecular weight von Willebrand Factor among other coagulation factors. Using a plastic pipette, remove the top 2/3 of plasma and transfer to labeled plastic tubes and cap. Glass tubes are unacceptable because glass activates the hemostatic mechanism.
  • If necessary, transfer plasma to a plastic tube and re-centrifuge to remove platelets. Platelet poor plasma is critical for the detection of lupus anticoagulants.
  • Samples must be frozen within 4 hours of collection (Quick freeze at -60°C or colder. Samples stored at -80°C are stable for 1 year; samples stored at -20°C are stable for only 2 weeks.)
  • Samples must remain frozen during storage and shipment. Ship on dry ice with guaranteed overnight delivery.

Clinical Research Testing

OHSU Lab Services is here to support your clinical research. Most of our laboratory tests can be performed as part of clinical research studies at a discounted price. Please visit the Clinical Research Services Office website for more details.