Our July, 2017 Quick Question was, "How do you store plasma specimens when coagulation testing is delayed to beyond 48 hours?"
We totaled 86 responses, and here are the results:
- Controlled refrigerator at 1–6°C 9% (8)
- Controlled freezer at –20°C 33% (28)
- Household freezer at ~ –20°C 3% (3)
- Controlled freezer at –70°C 55% (47)
Coagulation specimen storage is addressed in the Clinical and Laboratory Standards Institute approved guideline, CLSI H21-A5, Collection, thransport, and processing of blood speicmens for testing plasma-based coagulation assays and molecular hemostasis assays; Approved Guideline--5th Edition, 2008. The guideline discourages refrigerator storage with this phrase, "Storage at 2–4°C is not recommended, as it may result in cold activation of factor VII and therefore alter PT results." Also, H21 states, "Samples that will be subjected to testing of factor VIII activity, VWF activity, or for evaluation of VWF multimers should not be stored at 2–4°C and are better stored at room temperature, as cold temperatures may lead to gradual loss of VWF and factor VIII activity, potentially leading to a spurious diagnosis of VWD , misclassification of the type of VWD , or spurious diagnosis of factor VIII deficiency."
CLSI H21 encourages –70°C storage of platelet poor plasma when the storage time is indefinite, and permits storage in a controlled –20°C freezer for up to two weeks. The document prohibits use of household freezers with this statement, "A freezer that undergoes automatic freeze/thaw cycles (frost-free freezer, a unit where the temperature is cycled several times per day) is not acceptable as it may result in the cold activation of factor VII."
Consequently, tthose who answered "Controlled refrigerator at 1–6°C" or "Household freezer at ~ –20°C", should consider the approved methods.
Here is a 2017 review on coagulation specimen management:
Toulon P, Metge S, Hangard M, et al. Impact of different storage times at room temperature of unspun citrated blood samples on routine coagulation tests results. Results of a bicenter study and review of the literature. Int J Lab Hem. 2017;1–11