Appropriate collection and processing of specimens being tested for cryofibrinogens
Blood is collected in nonheparinized tubes (use EDTA or citrate) that do not allow coagulation and is stored at 37°C until centrifugation. After centrifugation, the remaining plasma is stored at 4°C for 72 hours and cryofibrinogens, if present, will form during this period.
Cryofibrinogens are absorbed by red blood cells (RBCs), so a delay in centrifugation or allowing the sample to cool may result in false-negative results because the RBCs are eventually discarded.
Heparin tubes should not be used for collection because heparin may form a cryoprecipitate with plasma factors and lead to false-positive results. It is also recommended that a separate serum sample be obtained by collecting blood in a prewarmed tube that does allow coagulation. The serum sample should be tested for the presence of cryoglobulins as outlined in Question 4.
Pearl: cryofibrinogens will precipitate in the cold only from the plasma sample, whereas cryoglobulins precipitate in the cold from both the plasma and serum samples.
