title: Influence of freeze-drying on the clotting properties of fibrinogen in plasma.
abstract: Freeze-dried plasma standards are often used to calibrate fibrinogen assays. Little is known, however, about the effect of freeze-drying on the clotting properties of fibrinogen. If these properties are altered, the use of freeze-dried calibration standards might influence the results obtained when applying clotting assays to determine fibrinogen concentrations. In order to disclose any discrepancies in fibrinogen concentrations before and after freeze-drying, we determined the fibrinogen concentrations in citrated plasma samples using a total clottable protein method and a clotting-rate assay before and after freeze-drying. When using the clotting-rate assay, significantly higher fibrinogen concentrations were found in fresh-frozen plasma samples compared to freeze-dried samples (P<.001). In freeze-dried plasma samples, the fibrinogen concentrations were significantly higher using the total clottable protein assay than the clotting-rate assay (P<.001). When measuring the fibrinogen concentrations in plasma samples with a wide range of fibrinogen concentrations using the routinely employed clotting-rate assay, significantly higher fibrinogen concentrations were found using the freeze-dried calibration plasma, than the fresh-frozen calibration plasma (P=.02). We conclude that the clotting rate of fibrinogen in citrated plasma is reduced following freeze-drying. When using freeze-dried calibration plasma in a clotting-rate assay, higher fibrinogen concentrations are obtained than by using fresh-frozen plasma. Denaturation of fibrinogen during the freeze-drying process, affecting its polymerization properties, may constitute the main contributor to the reduced clotting rate of freeze-dried plasma.
authors.affiliation: Haematological Research Laboratory, Ullevål University Hospital, Oslo, Norway. Tors-jen@online.no
authors.forename: Torstein
authors.initials: T
authors.lastname: Jensen
authors.forename: Sigrun
authors.initials: S
authors.lastname: Halvorsen
authors.forename: Hans C
authors.initials: HC
authors.lastname: Godal
authors.forename: Ole H
authors.initials: OH
authors.lastname: Skjønsberg
mesh_terms: D000328:Adult; D000368:Aged; D001777:Blood Coagulation; D001780:Blood Coagulation Tests / Q000379:methods / Q000592:standards; D002138:Calibration; D005260:Female; D005340:Fibrinogen / Q000032:analysis*; D005612:Freeze Drying; D006801:Humans; D008297:Male; D010949:Plasma / Q000737:chemistry
chemical_list: D005340:Fibrinogen