Specimen Management

From Joanna Carroll: I was recently told that samples should be double spun prior to long term freezing. Except in the case of heparin testing, I cannot find any evidence to support this. Also can you tell me if there are recommendations on how to handle samples for fibrinogen, D-dimer and unfractionated heparin anti-Xa assays? Our fibrinogen package insert only mentions how long the sample is good for at room temperature, and our D-dimer insert only mentions how to handle the sample after freezing. The CLSI document does not cover these tests. Thanks for your help.
Hello, Joanna, and thank you for your questions. The CLSI H-21 guideline provides answers to some, though not all of your questions. Coagulation specimens are transported at ambient temperatures and centrifuged to produce plasma with a platelet count <10,000/uL, often called platelet-poor plasma. This may be achieved with a single ambient temperature spin at 1500 g for at least 15 minutes. Operators with low-speed centrifuges may need to “double-spin,” which means to spin the separated plasma a second time, and those with high-speed centrifuges such as the Stat-spin may shorten the spin time. The guideline recommends confirming the resultant plasma platelet counts at least every six months. Platelet-poor plasma is preferred because platelets release platelet factor 4, coagulation factor V, and membrane phospholipids during storage and freezing. These can influence a number of test results, especially those for heparin monitoring and lupus anticoagulant testing.
Platelet-poor plasma is not required for fibrinogen or D-dimer assays, nor for prothrombin time (PT) or partial thromboplastin time (PTT), provided the assays are performed within the appropriate time intervals, so lab directors may take a less rigorous approach, however most find it more efficient to centrifuge all specimens the same way, particularly as additional tests may be added later.
Heparin monitoring specimens collected in 3.2% sodium citrate are centrifuged within one hour of collection and the plasma separated to avoid heparin neutralization by platelet factor 4. Specimens for PT may be held stoppered at room temperature for up to 24 hours. No trials have been held to learn about specimen stability for fibrinogen or D-dimer testing, however most laboratory directors adhere to the same standards they use for PT testing.
Finally, frozen specimens are rapidly thawed at 37C, thoroughly mixed, and assayed immediately after thawing.