Sample Collection for Coagulation Testing
1. Collection Tube. Blood should be collected in a blue-top tube containing 3.2% buffered sodium citrate.
Note: Please examine specimen collection and transportation supplies to be sure they do not include .
2. High Hematocrit Samples. Patients with elevated hematocrits have a relatively low amount of plasma for a given whole blood [collection] volume. This tends to increase the plasma citrate concentration effectively. If the patient has a known hematocrit >55%, the amount of citrate in the collection tube must be decreased according to the formula below.
The equation in CLSI H21 is as follows:
C = [1.85 x 10−3] [100−Hct] [Vblood]
Where:
C is the volume of citrate remaining in the tube.
Hct is the patient's hematocrit.
V is the volume of blood added to the evacuated tube.
Example:
Patient hematocrit = 60%
Total volume = 5 mL [standard citrated plasma collection tube volume]
C = [0.00185] x [100-60] x 4.5
C = [0.00185] x 180 [or 40 x 4.5]
C = 0.333
3. Order of Draw. A discard tube is not required prior to collection of coagulation samples, except when using a safety winged blood collection device [ie, "butterfly"], in which case a discard tube should be used. When noncitrate tubes are collected for other tests, collect sterile and nonadditive [red-top] tubes prior to citrate [blue-top] tubes. Any tube containing an alternate anticoagulant should be collected after the blue-top tube. Gel-barrier tubes and serum tubes with clot initiators should also be collected after the citrate tubes.
4. Venipuncture Technique. To avoid activation of the sample, the venipuncture should be clean, with minimal trauma. The tourniquet should be in place only as long as is needed to identify a vein and should never be in place for longer than one minute. Severely hemolyzed samples are not acceptable.
5. Safety winged blood collection kits [butterfly] must use a discard lead tube prior to collecting specimen tube to submit for testing. Failure to use a discard tube may lead to underfilling of the evacuated tube.
6. Fill Volume. Evacuated collection tubes must be filled to completion to ensure that a 9:1 blood-to-anticoagulant ratio is achieved. Under-filling of citrate collection tubes results in an increased anticoagulant-to-blood ratio and can extend clot-based coagulation assays. Note: Never combine two underfilled tubes together.
Please print and use the to ensure proper draw volume.
7. Mixing. The sample should be mixed immediately by three to six complete gentle end-over-end inversions to ensure adequate mixing of the anticoagulant with the blood.
8. Plasma Processing. Process the sample as soon as possible [preferably within 30 minutes of collection]. Centrifuge at an adequate speed and duration to achieve platelet-poor plasma [